Inorganic Scintillators and their Applications

IEEE 9th International Conference on Inorganic Scintillators and their Applications June 4 – 8, 2007 Wake Forest University Winston-Salem, NC USA P...
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IEEE 9th International Conference on

Inorganic Scintillators and their Applications June 4 – 8, 2007

Wake Forest University Winston-Salem, NC USA

Program and Abstracts IEEE 9th International Conference on

Inorganic Scintillators and their Applications i

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Foreword Beginning in 1992, the SCINT conferences on Inorganic Scintillators and their Applications have been bringing together researchers from across the world in the science, development, and applications of materials and detectors for registration of the energies and trajectories of high-energy radiation. Such detectors are important for applications ranging from port and airport security to medical imaging to oil exploration, and for large international experiments in high-energy particle physics and astrophysics. To foster international involvement and communication, the SCINT conferences have moved around quite widely, being held in Chamonix, San Francisco, Delft, Shanghai, Moscow, Chamonix, Valencia, and last in the Crimean city of Alushta. Wake Forest University in Winston-Salem, NC, USA welcomes the IEEE 9th International Conference on Inorganic Scintillators and their Applications, June 4-8, 2007. Topics of interest at the meeting range from fundamental processes of radiation interaction and light emission to crystal growth, defects, material engineering, quality inspection, and applications. At SCINT 2007 there are 59 oral presentations in plenary sessions, including 12 invited keynote lectures. There are 130 scientific poster presentations. There are 8 industrial exhibitors at SCINT 2007 who share both the exhibition hall and the show schedule with the scientific poster presentations. That is, the scientific posters and the exhibits are open for viewing during all 5 days of the conference, but are specially featured, attended, and accompanied by refreshments in the sessions on Monday afternoon, Tuesday afternoon and evening, and Thursday afternoon. There are approximately 200 registered participants at SCINT 2007 coming from 25 different nations. This is the first year in which a SCINT conference is technically co-sponsored by the Institute of Electrical and Electronics Engineers (IEEE), specifically by the Nuclear and Plasma Sciences Society (NPSS) of IEEE. This co-sponsorship has been important for visibility of SCINT 2007 and for attracting new participants. The refereed proceedings from SCINT 2007 will be published in the IEEE Transactions on Nuclear Science. We gratefully acknowledge financial support from the Publication and Research Fund of the Graduate School of Wake Forest University to defray the cost of meeting spaces. Likewise we acknowledge financial sponsorship of several conference functions and costs by Hilger Crystals, by Photonis, and by Saint-Gobain Crystals. We thank all exhibiting companies listed on the Exhibition page of this program book for the effective sponsorship represented by their participation. All sponsor funds along with participants’ fees have enabled the conference to waive 22 conference fees and provide housing for 14 participants, thus enabling wide participation from varied locations and institutions. For that, for the science presented, and for the communication/comaraderie achieved, the organizers acknowledge gratefully all participants in SCINT 2007. Such a meeting cannot be conducted successfully without the work of many volunteers, represented in the committee lists that follow and especially in the volunteer list following. The Physics Department of Wake Forest University is a particular source of volunteers at this conference. Undoubtedly there will be volunteers pitching in who were not listed at the time of printing, so please thank them too when you see them.

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SCINT 2007 Committees Organizing Committee Kim Ferris Chuck Melcher William Moses Pete Santago Richard Williams (chair) K. Burak Ucer

Pacific Northwest National Laboratory University of Tennessee Lawrence Berkeley National Laboratory Wake Forest University Medical School Wake Forest University Wake Forest University

International Advisory Committee J. Benlloch P. Dorenbos K. Fukuda A.V. Gektin M. Kobayashi M. Korzhik M. Lebeau P. Lecoq J.A. Mares C.L. Melcher V.V. Mikhailin

Spain Netherlands Japan Ukraine Japan Belarus Switzerland Switzerland Czech Republic USA Russia

W.W. Moses C. Pedrini P. Rodnyi B. Shulgin S. Tavernier C.W.E.van Eijk M.J. Weber R.T. Williams A.J. Wojtowicz C. Woody R.Y. Zhu

Guest Editor for the Proceedings of SCINT 2007 Chuck Melcher Volunteers Paul Anderson Keith Bonin Eric Carlson Woon-Seng Choong Lou-Trice Gamble Martin Guthold Natalie Holzwarth Martin Janecek

Jerry Kielbasa Jed Macosko Howard Shields Judy Swicegood Andrew Wall Windham Wilkinson Jack Williams Yaochun Zhang

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USA France Russia Russia Belgium Netherlands USA USA Poland USA USA

Exhibitors

Saint-Gobain Crystals

Hilger Crystals

Photonis Group

Furukawa Co., Ltd.

Aldrich-APL, LLC

ICx Radiation

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Exhibitors (cont.)

Chemetall GmbH

Bridgeport Instruments, LLC CAEN S.p.A. W-ie-ne-r Plein & Baus GmbH

Co-Sponsoring Organizations

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Brendle Hall

Physics Dept. (Olin Laboratory)

Benson Center Exhibition, Posters and Wednesday Oral Session

Reynolda Hall Magnolia Room Fresh Food Co.

Polo Residence

Sundance Plaza Hotel

Session Locations

Brendle Auditorium

Brendle Hall, 2nd Floor (Oral Sessions - except Wednesday)

Pugh Auditorium

Benson Center, 2nd Floor (Wednesday Oral Session G)

Benson 401

Benson Center, 4th Floor (Poster Sessions and Exhibits)

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General Schedule of Events

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Sunday, June 03, 2007 Times

Event/Session

Location

4:00 PM

10:00 PM

On-Site Registration

Polo Residence

7:00 PM

10:00 PM

Welcome Picnic

Polo Residence

Monday, June 04, 2007 Times

Event/Session

Location

8:30 AM

8:35 AM

Opening Remarks

Brendle

8:40 AM

10:00 AM

Oral Session A

Brendle

10:00 AM

10:40 AM

Coffee Break

Brendle

sponsored by Photonis

10:40 AM

12:15 PM

Oral Session B

Brendle

12:20 PM

1:55 PM

Lunch

Magnolia Room

2:00 PM

3:30 PM

Oral Session C

Brendle

3:40 PM

6:30 PM

Monday Poster & Exhibits

Benson 401

refreshments sponsored by Saint-Gobain

6:30 PM

Dinner

Surrounding restaurants

Tuesday, June 05, 2007 Times

Event/Session

Location

8:30 AM

10:00 AM

Oral Session D

Brendle

10:00 AM

10:40 AM

Coffee Break

Brendle

10:40 AM

12:15 PM

Oral Session E

Brendle

12:20 PM

1:55 PM

Lunch

Magnolia Room

2:00 PM

3:30 PM

Oral Session F

Brendle

3:40 PM

6:30 PM

Tuesday Poster & Exhibits

Benson 401

Dinner (free with badge)

Fresh Food Co.

Tuesday Poster & Exhibits

Benson 401

6:30 PM 7:30 PM

10:00 PM

(w/coffee & dessert)

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Wednesday, June 06, 2007 Times 8:30 AM 10:30 AM

10:30 AM 10:30 PM

Event/Session

Location

Oral Session G Excursion

Pugh

Thursday, June 07, 2007 Times 8:30 AM 10:00 AM 10:40 AM 12:20 PM 2:00 PM 3:40 PM 6:30 PM

10:00 AM 10:40 AM 12:15 PM 1:55 PM 3:30 PM 6:30 PM

Event/Session

Location

Oral Session H Coffee Break Oral Session I Lunch Oral Session J Thursday Poster & Exhibits Dinner

Brendle Brendle Brendle Magnolia Room Brendle Benson 401 City restaurants

Event/Session

Location

Oral Session K Coffee Break Oral Session L Closing Session Jazz on Fourth

Brendle Brendle Brendle Brendle Downtown

Friday, June 08, 2007 Times 8:30 AM 10:00 AM 10:40 AM 12:15 PM 7:00 PM

10:00 AM 10:40 AM 12:15 PM 12:55 PM

(downtown concert)

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June 3, 2007

June 4, 2007 Formal Opening & Oral A

June 5, 2007 Oral D

Airport Arrivals Commercial shuttles run all day (Also on Satuday, June 2)

Coffee Break

Coffee Break

8:30 AM 9:00 AM 10:00 AM 11:00 AM 12:00 PM

Oral B

Oral E

Lunch

Lunch

June 6, 2007 Oral G

Excursion

June 7, 2007 Oral H

June 8, 2007 Oral K

Coffee Break

Coffee Break

Oral I

Oral L

Lunch

Closing Session Airport Departures Commercial shuttles run all day

1:00 PM 2:00 PM

Oral C

Oral F

Oral J

Monday Poster and Exhibits

Tuesday Poster and Exhibits

Thursday Poster and Exhibits

3:00 PM 4:00 PM

On-Site Registration

5:00 PM Banquet

6:00 PM Dinner 7:00 PM 8:00 PM 9:00 PM

Dinner

Dinner

Welcome Picnic

Jazz on Fourth Tuesday Poster and Exhibits w/coffee & dessert

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June 9, 2007 Airport Departures Commercial shuttles run all day

Scientific Program

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Monday, June 04, 2007 8:30 AM

01 - ORAL A

8:30 AM 8:40 AM

OA1

9:10 AM

OA2

9:30 AM

OA3

9:45 AM

OA4

11:15 AM 11:30 AM 11:45 AM 12:00 PM

2:00 PM 2:00 PM 2:30 PM 2:45 PM 3:00 PM 3:15 PM

Chair: R-Y. Zhu

Opening Remarks RT Williams The CMS calorimeter in 2007: performance and physics goals P Lecoq The electromagnetic calorimeter of the Panda detector at FAIR/GSI B Lewandowski Overview of the 63000 PWO barrel crystals for CMS_ECAL production E Auffray Calorimeters with scintillators at the future linear collider J Cvach

10:40 AM 02 - ORAL B 10:40 AM

Brendle

Brendle

Chair: C. Pedrini

OB1 Scintillator materials – achievements, opportunities and puzzles M Nikl OB2 Atomistic simulation of defects in wide band gap scintillators CR Stanek, KJ McClellan, BP Uberuaga, MR Levy, RW Grimes OB3 Data-driven exploration of the ionization-phonon partitioning in scintillating radiation detector materials KF Ferris, BM Webb-Robertson, DV Jordan, DM Jones OB4 Scintillation response of Ce-doped garnets, perovskites and silicates under α, β and γ radiation JA Mares, M Nikl, E Mihokova, A Beitlerova, A Vedda, C D’Ambrosio OB5 Point defects as a limiting factor for Ce3+ emission AV Gektin, NV Shiran, S Neicheva, V Nesterkina, V Voronova

03 - ORAL C

Brendle

Chair: P. Dorenbos

OC1 Scintillator non-proportionality WW Moses OC2 Energy resolution of scintillation detectors - new observations M Moszynski, A Nassalski, A Syntfeld-Kazuch, LM Swiderski OC3 From luminescence nonlinearity to scintillation nonproportionality AN Vasil'ev OC4 Kinetic Monte Carlo model of scintillation mechanisms in activated alkali halides and evaluation of their contribution to nonlinear response S Kerisit, KM Rosso, BD Cannon OC5 Non-proportionality of organic scintillators and BGO A Nassalski, M Moszynski, A Syntfeld-Kazuch, LM Swiderski

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3:40 PM

04 - Monday Poster

Benson 401

PMo01 Production and development of scintillation materials at Bogoroditsk Technical Chemical Plant AV Baberdin, I Korneev, M Korzhik PMo02 Position resolution in LaBr3 scintillators using multi-anode photomultiplier tubes PF Bloser, M McConnell, JR Macri, JM Ryan, MV Amaresh Kumar PMo03 Measurement of photomultiplier gain using LYSO afterglow D Brasse, S Salvador, JL Guyonnet PMo04 Pixelated scintillator for X-ray imager and its effect on light output and spatial resolution BK Cha, B-J Kim, C Lee, JH Bae, H Kim, G Cho PMo05 Measurements of x-ray imaging performance of granular phosphors M Cho, SM Youn, C Lim, HK Kim, H Cho, JM Kim PMo06 Performance of a facility for measuring scintillator non-proportionality W Choong, G Hull, WW Moses, KM Vetter, SA Payne, NJ Cherepy, JD Valentine PMo07 Advances in yield calibration of scintillators JTM de Haas, P Dorenbos PMo08 Small size CsI(Tl) spectrometry efficiency and properties dependence on temperature E Dolev, A Manor, I Brandys, D Tirosh, G Ziskind, I Orion PMo09 Generation of defects in inorganic scintillators under small dose rate irradiation E Auffray, A Borisevich, V Dormenev, G Drobychev, M Korzhik, P Lecoq PMo10 The antisite defect-related trap in YxLu1-xAlO3:Ce single crystals M Fasoli, I Fontana, E Mihokova, M Nikl, A Vedda, YV Zorenko, V Gorbenko PMo11 On the energy resolution optimization of CsI(Tl) crystals for the R3B calorimeter MM Gascon, H Alvarez-Pol, J Benlliure, E Casarejos, D Cortina, I Durán PMo12 Scintillation properties of 1 inch Cs2LiYCl6:Ce crystals J Glodo, WM Higgins, EV Van Loef, KS Shah PMo13 Luminescence properties of ZnO nanocrystals and ceramic L Grigorjeva, D Millers, J Grabis, C Monty, A Kalinko, K Smits, V Pankratov PMo14 Spectroscopic studies of Ce3+ ions in lead fluoride U Happek, JA Campbell PMo15 Design of an apparatus to measure optical reflectance of scintillating crystal surfaces M Janecek, WW Moses PMo16 Design and characterization of CMOS avalanche photodiode with charge sensitive preamplifier YS Kim, JW Park, K Kim PMo17 Scintillator and CMOS APS imager for radiography conditions KH Kim, IS Hwang, YS Kim PMo18 The performance of X-ray scanner using ceramic scintillator base detector module G Cho, B Cha, DK Kim, SE Yun, KH Kim PMo19 Characteristics of europium-doped Gd2O3 phosphors for diagnostic x-ray imaging detectors S-Y Kim, S Kang, S Cho, J Park, S Heo, S Nam PMo20 Probing the concepts of photonic crystals on scintillating materials M Kronberger, P Lecoq, E Auffray PMo21 Improving the light yield of scintillating crystals by surface treatment M Kronberger, P Lecoq, E Auffray PMo22 Optimization of scintillation crystal geometry and finish for moment based depth of interaction detection CW Lerche, A Ros, A Munar, F Sánchez, JM Benlloch, V Herrero, R Esteve, A Sebastiá PMo23 Optical and scintillation properties of heavy crystal scintillators R Mao, L Zhang, R Zhu

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PMo24 NaI(Tl) measurements and simulations of Compton effect based calibration system development C Morhaim, I Yaar, I Orion PMo25 Growth and scintillation properties of large size LuYAP crystals MM Musolino, A De Simone, A Morbiato, S Janus, AJ Wojtowicz, J-L Lefaucheur PMo26 La3+, Y3+, Yb3+ - impurity effect on cross-luminescence of BaF2crystals AS Myasnikova, EA Radzhabov, AS Mysovsky PMo27 Performance of PWO-II prototype arrays for the EMC of PANDA RW Novotny, W Döring, V Dormenev, P Drexler, W Erni, M Rost, M Steinacher, M Thiel, A Thomas PMo28 Suppression of host luminescence in the Pr:LuAG scintillator H Ogino, K Kamada, A Yoshikawa, J Pejchal, M Nikl, A Vedda, J Shimoyama, K Kishio PMo29 Surface passivation effect on CZT Schottky and Ohmic contacts SH Park, JH Ha, YH Cho, HS Kim, SM Kang, YK Kim, JK Kim PMo30 Relaxed electronic excitations in lead tungstate crystals A Rakov, AA Islamov, SK Ismoilov PMo31 Study of the relationship between scintillator electron response non proportionality and gamma ray energy resolution BW Reutter, WW Moses, W Choong PMo32 Transfer and trapping of electrons in crystals CaF2-O2- and CaF2-Eu2+ VV Pologrudov, RY Shendrik, AP Redina PMo33 Modifications of light emission spectra and atomic structure of europium molybdate bulk crystals by high pressure and thermal treatments SZ Shmurak, AP Kiselev, NV Klassen, VV Sinitsyn, IM Shmyt’ko, BS Red’kin, SS Khasanov PMo34 Scintillation properties of pure CsI and CsI doped with CsBr LM Swiderski, M Moszynski, A Nassalski, A Syntfeld-Kazuch, W Klamra PMo35 Light pulse shape dependence on γ-rays energy in CsI(Tl) A Syntfeld-Kazuch, M Moszynski, LM Swiderski, W Klamra, A Nassalski PMo36 Design rules for scintillating radiation detection materials: compromises between luminosity, stopping power, and efficiency BM Webb-Robertson, KF Ferris, DV Jordan, DM Jones PMo37 Large area APDs for the PANDA-EMC A Wilms, H Nowak, K Peters PMo38 Single crystal growth and luminescence properties of CeF3-CaF2 solid solution grown by the micro-pulling-down method A Yoshikawa, K Aoki, K Kamada, KJ Kim, M Nikl PMo39 Comparison of Pr:{Lu}3[Ga,Al]2[Al]3O12(LuGAG) single crystal grown by the micro-pulling-down method and Cz method A Yoshikawa, K Kamada, H Ogino, H Sato, M Nikl PMo40 Imaging characteristics of a-Se based hybrid-type flat panel detector using high resolution phosphor screen B Cha, D Son, M Yun, J Park, C Mun, S Nam PMo41 Radiation damage in large size LSO and LYSO crystal samples L Zhang, J Chen, R Mao, R Zhu PMo42 Intrinsic and Ce3+ related luminescence of the single crystal and single crystalline films of YAP and YAP:Ce perovskites: new results YV Zorenko, V Gorbenko, A Voloshinovskii, V Vistovskii, M Nikl, E Mihokova, A Vedda, M Fasoli, K Nejezchleb

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Tuesday, June 05, 2007 8:30 AM 8:30 AM 9:10 AM

9:30 AM 9:45 AM

05 - ORAL D

11:15 AM 11:30 AM 11:45 AM 12:00 PM

2:00 PM 2:00 PM 2:35 PM

3:00 PM 3:15 PM

Chair: K. Ferris

OD1 Scintillators for security applications AJ Peurrung OD2 Li-based thermal neutron scintillator research; Rb2LiYBr6: Ce3+ and other elpasolites MD Birowosuto, P Dorenbos, JTM de Haas, CWE van Eijk, KW Krämer, HU Güdel OD3 Evaluation of melt-grown, ZnO single crystals for use as α-particle detectors JS Neal, NC Giles, DJ Wisniewski, LA Boatner, V Rengarajan, J Nause, B Nemeth OD4 Gamma ray imaging with LaBr3:Ce scintillators B Budden, GL Case, M Cherry, J Isbert, M Stewart

10:40 AM 06 - ORAL E 10:40 AM

Brendle

Brendle

Chair: A. Wojtowicz

OE1 New cerium-activated phosphate glass scintillators LA Boatner, DJ Wisniewski, JS Neal, JO Ramey, GE Jellison OE2 Luminescence and scintillation properties of Ce3+, Pr3+, and Sc3+ - doped Lu3Al5O12 ceramic EV Van Loef, C Brecher, KS Shah OE3 Growth and properties of LuAP:Ce with complex and simple substitutions AG Petrosyan, M Derdzyan, CG Pedrini, P Lecoq, I Kamenskikh, C Dujardin, K Ovanesyan OE4 Antisite Ce3+Al centers in perovskites and garnets: ESR and luminescence study V Babin, VV Laguta, A Makhov, K Nejezchleb, M Nikl, SG Zazubovich OE5 Czochralski growth and scintillation properties of 2inch-size Pr:Lu3Al5O12 (LuAG) single crystal K Kamada, K Tsutsumi, Y Usuki, H Ogino, A Yoshikawa

07 - ORAL F

Brendle

Chair: J. Mares

OF1 Physics of lead tungstate scintillators SG Zazubovich OF2 Radiation hardness and recovery processes of PWO crystals at –25°C RW Novotny, SF Burachas, W Döring, V Dormenev, YM Goncharenko, MS Ippolitov, A Hofstaetter, M Korzhik, V Manko, YM Melnick, O Missevitch, VV Mochalov OF3 Transformations of absorption and emission centers in PbWO4 P Bohacek, N Solovieva, M Nikl OF4 Scintillation mechanism in complex structure doped oxides and novel developments M Korzhik

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3:40 PM

08 - Tuesday Poster

Benson 401

PTu01 Comparison of LaBr3:Ce, LaCl3:Ce, CZT and NaI(Tl) for resolution of nuclear material spectra D Alexiev, L Mo, M Smith PTu02 Afterglow suppression and non-radiative charge-transfer in CsI:Tl,Sm RH Bartram, LA Kappers, DS Hamilton, A Lempicki, C Brecher, VB Gaysinskiy, EE Ovechkina, VV Nagarkar PTu03 Investigation of ZnWO4 crystals as an absorbers in the CRESST dark matter search IV Bavykina, G Angloher, F Proebst, F Petricca PTu04 Charge carrier and exciton dynamics in LaX3:Ce3+ scintillators (X=Br, Cl) GA Bizarri, P Dorenbos PTu05 An advanced scintillator-based Compton telescope PF Bloser, JM Ryan, M McConnell, JR Macri PTu06 Electronic structure studies of Ce-doped gamma detector materials AM Canning, R Boutchko, SE Derenzo, L-W Wang, MJ Weber PTu07 Luminescence and scintillation properties of barium and strontium iodides doped with rare-earth ions VL Cherginets, B Grynyov, N Galunov, T Ponomarenko, LN Trefilova, O Tarasenko, O Zelenskaya, V Alekseev, N Kosinov, A Litichevsky PTu08 ZnSe radiation detector with various signal collecting method YH Cho, SH Park, WG Lee, JH Ha, HS Kim, SM Kang, YK Kim, JK Kim, NG Starzhinskiy PTu09 Structural and scintillation properties of cerium–doped Ba2LaF7 and Ba2LaCl7 A Edgar, M Bartle, SG Raymond, GVM Williams, C Varoy PTu10 Vacuum deposited ZnSe(Te) scintillating layers A Fedorov, KA Katrunov, A Lalayants, V Nesterkina, NV Shiran, SE Tretyak PTu11 The ZnSe(O) - perspective scintillation material for medical computer tomography VD Ryzhikov, B Grynyov, SM Galkin, N Starginski, V Silin, S Naidenov, P Lecoq PTu12 Luminescence properties and morphology of ZnSe(Te) films VB Gaysinskiy, VV Nagarkar, B Singh, EE Ovechkina, SR Miller, S Thacker PTu13 Measurement and simulation of the neutron response and detection efficiency of a Pbscintillating fiber calorimeter M Anelli, G Battistoni, S Bertolucci, C Bini, P Branchini, C Curceanu, G De Zorzi, A Di Domenico, B Di Micco, A Ferrari, P Gauzzi, S Giovannella PTu14 Scintillation properties of a BaxSr1-xCl2 single crystal J Kim, H Kang, HJ Kim, H Park, S Kim, S-H Doh PTu15 Intrinsic luminescence of single crystalline films and single crystals of LuAP and LuAP:Ce perovskites YV Zorenko, V Gorbenko, T Voznyak, T Zorenko, V Mikhailin, M Kolobanov, N Petrovnin, D Spassky PTu16 Ce-doped YAG and LuAG epitaxial films for scintillation detectors M Kucera, K Nitsch, M Kubova, N Solovieva, M Nikl, JA Mares PTu17 Performance of an 8x8 array of LaBr3(Ce) pixels coupled to a multi- anode PMT S Kurosawa, K Hattori, S Kabuki, H Kubo, K Miuchi, H Nishimura, Y Okada, A Takada, T Tanimori, K Ueno PTu18 A method of sensitivity enhancement of liquid xenon emission detectors for dark matter search A Bolozdynya, A Bradley, P Brusov, E Dahl, J Kwong, T Shutt PTu19 Growth and scintillation properties of ZnSe:Te and ZnSe:Al,O,Te semiconductors W Lee, YK Kim, JK Kim, NG Starzhinskiy, VD Ryzhikov, B Grynyov PTu20 Luminescence properties of ZnSe:Te and ZnSe:O crystals grown by BridgmanStockbarger method W Lee, YK Kim, JK Kim, NG Starzhinskiy, VD Ryzhikov, B Grynyov

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PTu21 Monte Carlo modeling and analysis of structured CsI scintillator-coupled pixel detectors C Lim, HK Kim, H Cho PTu22 "Semi-transparent" X-ray beam monitor based on nanometric phosphor powder deposited on thin carbon plate T Martin, PP Jobert, F Lesimple, G Baret PTu23 CASTER – A LaBr3-based gamma ray imager for NASA’s Black Hole Finder Probe M McConnell, PF Bloser, GL Case, M Cherry, J Cravens, TG Guzik, K Hurley, RM Kippen, JR Macri, RS Miller, W Paciesas, JM Ryan PTu24 Using thin films to rapidly screen potential scintillators BD Milbrath, JA Caggiano, DW Matson, LC Olsen PTu25 EPR and luminescence of F+ centers in bulk and nanophosphor oxyorthosilicates W Cooke, MW Blair, JF Smith, BL Bennett, LG Jacobsohn, EA McKigney, RE Muenchausen PTu26 Application of 6LiI(Eu) scintillators with photodiode readout for neutron counting in mixed gamma-neutron fields G Pausch, J Stein PTu27 Combinatorial thin film synthesis of scintillation materials JD Peak, C Melcher, PD Rack PTu28 Charge transfer luminescence of Yb-doped oxide crystals: overview, new results and perspectives CG Pedrini, I Kamenskikh, AG Petrosyan, C Dujardin, G Ledoux, N Guerassimova, D Krasikov PTu29 Combinatorial chemical synthesis of scintillator materials JD Powell, E Bourret-Courchesne, M Boswell, TF Budinger, SE Derenzo, CA Ramsey, DS Wilson PTu30 Thin LSO-based scintillating mixed-crystal grown by liquid phase epitaxy for high resolution X-ray imaging A Rack, T Martin, M Couchaud, P-A Douissard, A Cecilia, A Danilewsky, T Baumbach PTu31 Energy dissipation in impurity doped alkaline-earth fluorides EA Radzhabov, M Kirm, A Egranov, A Nepomnyaschikh PTu32 Influence of RE-doping on the scintillation properties of LSO crystals G Ren, L Qin, S Lu, D Ding, S Pan PTu33 The promising detectors for nuclear planetology A Rogozhin, IG Mitrofanov, AS Kozyrev, MS Litvak, AB Sanin, V Tretyakov, NP Kuzmina PTu34 EPR of intrinsic radiation defects in LiYF4 crystal A Fedotovs, U Rogulis, L Dimitrocenko PTu35 Luminescence and scintillation characteristics of the SrCl2 single crystal for the neutrinoless β+/EC decay search G Rooh, H Kang, HJ Kim, H Park, S-H Doh PTu36 Intrinsic luminescence and band structure of Lu2SiO5 and Y2SiO5 crystals ES Shlygin, VV Mazurenko, V Ivanov, V Pustovarov, M Kuznetsov, A Kruzhalov, B Shulgin PTu37 Electronic structure of Pb- and non-Pb based phosphate scintillators DJ Singh, GE Jellison, LA Boatner PTu38 Radiative decay of electronic excitations in ZrO2 nanocrystals and macroscopic single crystals K Smits, L Grigorjeva, D Millers, JD Fidelus, W Lojkowski PTu39 Brighter and faster LSO:Ce MA Spurrier, P Szupryczynski, AA Carey, C Melcher PTu40 Novel trends in development of A2B6-based scintillators NG Starzhinskiy, B Grynyov, L Gal’chinetskii, VD Ryzhikov, V Silin PTu41 Positron lifetime calculations for ZnO with vacancies H Takenaka, DJ Singh

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PTu42 High-energy photon detection with LYSO crystal array M Thiel, W Döring, V Dormenev, P Drexler, RW Novotny, M Rost, A Thomas PTu43 Industrial application of detectors on the basis of “scintillator-photodiode”system TV Tkacheva PTu44 Novel technique of scintillator CsI (Tl) crystal growth TV Tkacheva, MA Gonik PTu45 Trapping and migration of polarons and excitons in scintillators: CsI and LaBr3 RM Van Ginhoven, JE Jaffe, S Kerisit, KM Rosso PTu46 Ce3+ doped KDP crystals, a new scintillation detector for registration of neutrons in high-intensity mixed (n, γ)-fields AP Voronov, VI Salo, GN Babenko, VM Puzikov, YuT Vydai PTu47 Development of novel polycrystalline ceramic scintillators DJ Wisniewski, LA Boatner, JS Neal, GE Jellison, JO Ramey, A North, M Wisniewska, A Lempicki, C Brecher PTu48 A fast screening technique to evaluate scinitllation response Y Zhang, BD Milbrath, JA Caggiano, WJ Weber

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Wednesday, June 06, 2007 8:30 AM 8:30 AM 9:05 AM 9:25 AM 9:40 AM 10:15 AM

09 - ORAL G

Pugh

Chair: C. Woody

OG1 Scintillators in interplanetary space missions A Owens OG2 The Lunar Occultation Observer (LOCO): A hard x-ray all-sky survey mission concept RS Miller OG3 CeBr3 scintillator development for space missions W Drozdowski, P Dorenbos, AJJ Bos, A Owens, FGA Quarati OG4 Scintillators for geophysical exploration B Roscoe OG5 (Lu-Y)AlO3:Ce scintillator for well logging AV Baberdin, A Dutova, AA Fedorov, M Korzhik, V Ligoun, O Missevitch, V Kazak, A Vinokurov, S Zagumenov

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Thursday, June 07, 2007 8:30 AM 8:30 AM 9:00 AM 9:30 AM 9:45 AM

10 - ORAL H

11:00 AM 11:15 AM 11:30 AM 11:45 AM 12:00 PM

2:00 PM 2:00 PM 2:30 PM

2:45 PM 3:00 PM 3:15 PM

Chair: W. Moses

OH1 A history of PET instrumentation L Eriksson OH2 Special applications for scintillating crystals in medical imaging C Woody OH3 An operative mini gamma camera for sentinel lymph node procedure using a GSO:Ce inorganic scintillating crystal S Salvador, V Bekaert, C Mathelin, D Huss, JL Guyonnet OH4 Timing and energy response of six prototype scintillators CCM Kyba, J Glodo, EV Van Loef, JS Karp, KS Shah

10:40 AM 11 - ORAL I 10:40 AM

Brendle

Brendle

Chair: P. Lecoq

OI1 Liquid xenon scintillator for dark matter detection K Ni OI2 Development of low background CsI(Tl) crystals and search for WIMP H Kim, HS Lee, HC Bhang, JH Choi, H Dao, IS Hahn, HJ Hwang, SW Jung, WK Kang, DW Kim, SC Kim, SK Kim OI3 Luminescence of RE oversaturated crystals AV Gektin, NV Shiran, V Nesterkina, G Stryganyuk, K Shimamura, E Víllora, K Kitamura OI4 One-, two-, and nano-dimensional scintillators C Dujardin, P Anfré, D Amans, G Ledoux, C Leluyer, CG Pedrini OI5 Thermally induced 4f – 5d transitions in LuAlO3:Ce (LuAP) AJ Wojtowicz, S Janus OI6 Spatial distribution of electron-hole pairs created by photons in detector materials F Gao, LW Campbell, Y Xie, R Devanathan, AJ Peurrung, WJ Weber

12 - ORAL J

Brendle

Chair: M. Korzhik

OJ1 Combinatorial synthesis and scintillator development X Xiang OJ2 LBNL facility for new scintillator material discovery SE Derenzo, M Boswell, R Boutchko, TF Budinger, AM Canning, E BourretCourchesne, SM Hanrahan, M Janecek, JD Powell, Y Porter-Chapman, CA Ramsey, SE Taylor OJ3 Europium- or cerium-doped barium halide scintillators for x-ray and γ-ray detections J Selling, MD Birowosuto, P Dorenbos, S Schweizer OJ4 A ceramic version of the LSO scintillator A Lempicki, C Brecher, H Lingertat, S Miller, J Glodo, VK Sarin OJ5 Effect of codopants on luminescence of GdTaO4:Eu3+ scintillator M Gu, K Han, X Liu, L Xiao, S Huang, B Liu, C Ni

xxii

3:40 PM

13 - Thursday Poster

Benson 401

PTh01 Deep VUV scintillators for detectors working in cryogenic environment V Babin, E Feldbach, M Kirm, V Makhov, S Vielhauer PTh02 GdI3: Ce3+ and its performance against other iodide scintillators MD Birowosuto, P Dorenbos, CWE van Eijk, KW Krämer, HU Güdel PTh03 Luminescence properties of nano-sized x-ray phosphors prepared by solution combustion method S Cho, S Kang, B Cha, J-W Shin, C Kwon, S Nam PTh04 Monte Carlo simulation of spatial resolution in phosphor coupled CMOS-type digital mammography system S Kang, J-W Shin, S-Y Kim, C Choi, H Lee, S Nam PTh05 EPR spectra of radiation defects in YVO4 crystals A Fedotovs, V Pankratov, L Grigorjeva, D Millers, U Rogulis PTh06 Luminescence and afterglow of RE doped LiCaAlF6 and LiSrAlF6 crystals AV Gektin, NV Shiran, S Neicheva, G Stryganyuk, K Shimamura, E Víllora, K Kitamura PTh07 Scintillation properties of PbI2:Te J Glodo, EV Van Loef, WM Higgins, SE Derenzo, WW Moses, KS Shah PTh08 Mixed lutetium iodide compounds J Glodo, EV Van Loef, WM Higgins, KS Shah PTh09 Recent developments on LuAG:Ce single crystal fibers A Caramanian, J-M Fourmigué, D Perrodin, B Hautefeuille, B Lebbou, C Dujardin, O Tillement PTh10 Development of new technology for the manufacturing of nanocrystalline silicate scintillation materials N Jalabadze, R Chedia, T Kukava, L Nadaraia PTh11 Characterization of scintillation properties of Gd doped lead chloride at low temperature S Kim, HJ Kim, H Park, H Kang, S-H Doh PTh12 Luminescence and scintillation properties of CeBr3 single crystal S Ra, S Kim, HJ Kim, H Park, S Lee, H Kang, S-H Doh PTh13 Application of scintillating fibers for cross – bar radiation detector matrices NV Klassen, VN Kurlov, SZ Shmurak, IM Shmyt’ko, AA Asryan, AI Maksimov PTh14 Application of nanoscintillators for medical imaging and anticancer therapy NV Klassen, OA Krivko, VV Kedrov, VN Kurlov, SZ Shmurak, IM Shmyt’ko, GK Strukova, NP Kobelev, EA Kudrenko, IA Shikunova PTh15 Large volume CaMoO4 scintillation crystals M Korzhik, V Kornoukhov, O Missevitch, AA Fedorov, A Annenkov, O Buzanov, A Borisevich, V Dormenev, SK Kim, Y Kim, H Kim, A Bratyakina PTh16 Control of energy storage effect in Lu2SiO5:Ce3+ nanoclusters AA Masalov, OG Vyagin, II Ganina, YV Malyukin PTh17 SSPM readout of LSO, (Lu-Y)AP:Ce and PWO-II pixels for PET detector modules YV Musienko, E Auffray, AA Fedorov, M Korzhik, P Lecoq, S Reucroft, J Swain PTh18 Growth of ZnWO4 scintillation crystal for high sensitivity 2β experiments LL Nagornaya, AM Dubovik, YY Vostretsov, B Grynyov, FA Danevich, KA Katrunov, VM Mokina, GM Onyshchenko, DV Poda, IA Tupitsyna PTh19 New detection configuration for radio-HPLC based on organic and inorganic scintillation crystals A Osovizky, B Laster, E Dolev, AA Wilson, T Harris, T Bell, S Houle PTh20 Scintillation properties of CsI:Tl crystals codoped with Sm2+ VV Nagarkar, EE Ovechkina, VB Gaysinskiy, S Thacker, SR Miller, C Brecher, A Lempicki, RH Bartram PTh21 Time-resolved luminescence characteristics of nanocrystalline CaWO4 V Pankratov, L Grigorjeva, D Millers, A Kuzmin, A Kareiva

xxiii

PTh22 Growth and study of Yb-doped oxides for charge transfer luminescence AG Petrosyan, CG Pedrini, I Kamenskikh, G Shirinyan, K Ovanesyan, A Eganyan, T Butaeva, C Dujardin PTh23 Lanthanum halide scintillation spectrometer light yield and pulse shape for gammarays and particles FGA Quarati, S Brandenburg, P Dorenbos, W Drozdowski, RW Ostendorf, A Owens PTh24 Characterization by photoelectron and optical spectroscopies of RE doped sesquioxides HL Retot, B Viana, A Bessière, A Galtayries PTh25 Mixed KDP/ADP (K1-x(NH4)xH2PO4): Tl+ crystals, a selectively sensitive scintillator for registration of fast neutrons: growth and properties VI Salo, AP Voronov, SI Bondarenko, NI Eremin, VM Puzikov PTh26 On the luminescence of LuCl3:Pr3+ under 4f2 → 4f15d1 and band gap excitation AM Srivastava, SJ Duclos, HA Comanzo, SM Loureiro, JS Vartuli, U Happek, P Schmidt PTh27 Monte Carlo simulation of photon transport in a scintillation crystal array X Sun, Z Zhang, Z Wu, Y Liu, Y Jin PTh28 Signal processing of four joint H8500 under a scintillation crystal array X Sun, X Li, Y Liu, S Wang, Y Jin PTh29 YCl3:Ce and YBr3:Ce crystals as scintillation detectors of x- and soft γ-radiation LN Trefilova, B Grynyov, VL Cherginets, N Galunov, T Ponomarenko, O Tarasenko, O Zelenskaya, V Alekseev, N Kosinov, A Litichevsky PTh30 Photo- and radiation-stimulated processes in CsI(Tl) crystals LN Trefilova, B Grynyov, V Alekseev, A Mitichkin, V Yakovlev, A Meleshko PTh31 Fine granular calorimeter with scintillator strips and new photon sensor readout S Uozumi PTh32 Effect of calcining conditions on the valency state of Ce in SrHfO3 scintillators EV Van Loef, WM Higgins, C Brecher, A Lempicki, V Venkataramani, S Friedrich, KS Shah PTh33 Effect of excitation density on yield and non-exponential decay of CdWO4 STE emission AN Vasil'ev, N Fedorov, P Martin, M De Grazia, H Merdji, B Carré, J Gaudin, S Guizard, M Kirm, V Nagirnyi, AN Belsky PTh34 Applications of Monte Carlo method to simulate X-ray interaction in Xe Y Xie, F Gao, R Devanathan, AJ Peurrung, WJ Weber PTh35 Energy transfer to Pr3+ ions in Pr:Lu3Al5O12(LuAG) single crystal A Yoshikawa, K Kamada, H Ogino, T Katagiri, D Iri, M Itoh, M Fujita PTh36 Excitation energy transfer in CeF3 single crystals doped with Sr2+ A Yoshikawa, K Aoki, K Kamada, Y Tani, T Katagiri, D Iri, M Itoh, M Fujita PTh37 Cascaded model analysis of pixellated scintillator imaging detectors HK Kim, SM Youn, C Lim PTh38 Crystal growth and scintillating properties of Zr/Si-codoped YAlO3:Pr3+ M Zhuravleva, A Novoselov, A Yoshikawa, J Pejchal, M Nikl, JA Mares, A Vedda PTh39 Growth and luminescence properties of YAG and YAG:Ce single crystalline films grown by liquid phase epitaxy from Ba-based flux YV Zorenko, V Gorbenko, T Voznyak, M Nikl, JA Mares, A Vedda, M Fasoli PTh40 Growth and luminescence properties of AWO4 and AWO4 :Bi (A=Ca, Cd) single crystalline film scintillators YV Zorenko, V Gorbenko, I Konstankevych, A Voloshinovskii, V Savchyn, SG Nedilko, B Grynyov

xxiv

Friday, June 08, 2007 8:30 AM 8:30 AM 8:45 AM 9:00 AM

9:15 AM 9:30 AM 9:45 AM

14 - ORAL K

11:00 AM 11:15 AM 11:30 AM 11:45 AM 12:00 PM

12:15 PM 12:15 PM 12:45 PM

Chair: M. Nikl

OK1 Control of electron-phonon dynamics by quantum confinement in isolated Y2SiO5:Pr3+ nanocrystal YV Malyukin, AA Masalov, PN Zhmurin OK2 Luminescence properties of nanocrystalline YAG V Pankratov, D Millers, L Grigorjeva, T Chudoba OK3 Development of new technologies for the manufacturing of nanocrystalline scintillation materials N Jalabadze, R Chedia, T Kukava, L Nadaraia OK4 Science and application of nanophosphors RE Muenchausen, MK Bacrania, BL Bennett, R Del Sesto, RD Gilbertson, LG Jacobsohn, EA McKigney, JF Smith, S Stange, W Cooke OK5 Characterization of CsI:Tl recrystalization after liquid phase deposition UL Olsen, X Badel, J Linnros, T Martin, HF Poulsen, S Schmidt OK6 Scintillating silica fibers: microscopical material properties and in vivo dosimetry applications A Vedda, N Chiodini, D Di Martino, M Fasoli, F Moretti, M Nikl, N Solovieva, A Baraldi, E Buffagni, M Mazzera, R Capelletti, E Mones

10:40 AM 15 - ORAL L 10:40 AM

Brendle

Brendle

Chair: A. Gektin

OL1 Advancement in development of photomultipliers dedicated to new scintillators studies M Kapusta, P Lavoute, F Lherbet, C Moussant, P Hink OL2 Performance of 4.4-mm2 SiPMs with CMS HO in a CERN test beam AH Heering, J Rohlf, S Los, J Freeman, S Kuleshov, YV Musienko, S Banerjee OL3 Crystal growth and potential utilisation of single crystal fibers in medical devices B Hautefeuille, B Lebbou, C Dujardin, P Anfré, J-M Fourmigué, A Caramanian, D Perrodin, O Tillement, CG Pedrini OL4 Y3Al5O12:Ce and Lu3Al5O12:Ce garnets single crystal and single crystalline film scintillators: what are the centers of luminescence? YV Zorenko OL5 Advantages and problems of nanocrystalline scintillators NV Klassen, VV Kedrov, VN Kurlov, SZ Shmurak, IM Shmyt’ko, GK Strukova, NP Kobelev, EA Kudrenko, OA Krivko, AP Kiselev OL6 The quest for the ideal scintillator for hybrid phototubes BK Lubsandorzhiev

Closing Session

Brendle

Scientific summary C Melcher Announcement of SCINT 2009

xxv

Abstracts

1

OA1

The CMS calorimeter in 2007: performance and physics goals Paul Lecoq CERN, Geneva, Switzerland

Thirteen years after the decision to build a Lead Tungstate bades electromagnetic calorimeter for the CMS experiment at the Large Hadron Collider (LHC) at CERN the detector is now in its final assembly and installation phase for the LHC startup at the end of 2007. It is made of 75848 Lead Tungstate crystals, 61200 of 133 cubic centimeter for the barrel and 14648 of 189 cubic centimeter for the endcaps, for a total weight of 90 tons of crystals. This challenging project aims to achieve an extreme precision in photons and electrons energy measurement. General motivations, main technical challenges, measured performances, and the actual status of the project will be discussed.

2

OA2

The electromagnetic calorimeter of the Panda detector at FAIR/GSI Bernd Lewandowskia* on behalf of the Panda EMC group a

GSI, Planckstr. 1, Darmstadt, 64291, Germany

PANDA is a 4π detector planned for the antiproton storage ring at the International Facility for Antiproton and Ion Beams (FAIR) at the GSI[1]. The antiproton beam of excellent momentum resolution up to 15 GeV/c beam momentum allows experiments with an extremely high luminosity, that require a fast electromagnetic calorimeter of high granularity and resolution to measure photons of several GeV down to 10 MeV energy. The candidate for the fast scintillation material for this calorimeter is PbWO4 with significantly improved light yield by the production mechanism. A further increase of the light yield will be achieved by operating the EMC at a temperature of -25°C, which requires detailed studies of the response functions of PbWO4 to ensure the good energy and excellent time resolution. For the detection of scintillation light fast photosensors are required, which are operated in a magnetic field and cover a large part of the readout surface. Large Area Avalanche Photo Diodes (LAAPDs) have been developed for this purpose and prototypes with an active area of 10 × 10 mm2 have been studied. The operation of PbWO4 at -25°C readout by LAAPDs requires improved temperature stabilization to 0.1°C implying stringent conditions for the mechanical design. A thermal shielding has to enclose the active EMC volume, separating it from the surrounding detector volumes operating at +25°C, but placing only a minimum of radiation lengths in front of the detection side. Furthermore the radiation hardness of all components has to be investigated at this low temperature, starting with the single devices of crystals and LAAPDs, extending to large scale prototypes that contain the complete detection chain. The R&D work for the Panda EMC has reached the construction of a prototype containing 60 crystals. The studies foreseen for this device include detailed investigations of the operating conditions, being essential to ensure a reliable operation of the Panda detector in factory mode for ten years. * corresponding author e-mail:[email protected] References 1. PANDA Technical Progress Report, Darmstadt 2005.

3

OA3

Overview of the 63000 PWO barrel crystals for CMS_ECAL production E. Auffraya* on behalf of the CMS_ECAL group, a

CERN, route de Meyrin,Geneva, 1211, Switzerland

In February 2007, the PWO crystal production for the barrel part of the CMS electromagnetic calorimeter has been completed. Since September 1998, 63000 crystals (61000 in Russia, 2000 in China) have been produced, received and tested in two regional centers (CERN and INFN Rome). This paper presents an overview of the methods used from the R&D phase up to the final large scale reception and quality control. The crystals characteristics and the lessons learnt from the production of this unprecedented amount of crystals in a HEP experiment are also presented. * corresponding author e-mail: [email protected]

4

OA4

Calorimeters with scintillators at the future linear collider Jaroslav Cvachab a

Institute of Physics of the ASCR v.v.i., Na Slovance 2, Prague, 18221, Czech Republic b representing the CALICE Collaboration

The task of the calorimetry at the International Linear Collider (ILC) – a new electronpositron accelerator with the center-of-mass energy 0.5-1.0 TeV is to improve the energy resolution for jets by a factor of two with respect to the existing calorimeters. The prevailing opinion is that it can be reached by new hardware and software developments using very small calorimetry cells and the reconstruction method called the particle flow. We have built a 1 m3 prototype of a hadron calorimeter using scintillator tiles 5mm thick with sizes from 30x30 to 120x120 mm2 arranged in the 1 m2 planes interleaved by absorber plates from stainless steel (see Fig. 1). The prototype was successfully tested in the CERN beams in 2006 and the first results will be presented. The calorimeter uses a novel photodector a silicon photomultiplier (SiPM) which is placed in the scintillator.[1] The electric signals go directly from the tile via printed board connections below the scintillators to the front-end electronics placed on the calorimeter side. The setup is monitored and calibrated by short pulses of the UV LED light.

Figure 1: View of scintillator tiles in a 1 m2 plane of a calorimeter. The circles are from WLS fibers which bring light to SiPMs in a tile corner.

Other projects using scintillators in the ILC calorimetry will be shortly reviewed.[2] References 1. V. Andreev et al., Nucl. Instr. Meth. A540, 368 (2005). 2. see e.g. the recent review given by E. Garutti at the ILC workshop, Valencia 2006, http://ific.uv.es/~ilc/ECFA-GDE2006/.

5

OB1

Scintillator materials – achievements, opportunities and puzzles Martin Nikl* Institute of Physics AS CR, Cukrovarnicka 10, 16253 Prague, Czech Republic

Despite of the relatively long history of the development of scintillator and phosphor materials which started at the end of 19th century, within last two decades the scintillator characteristics and figure-of-merit of a number of new materials were studied and some of them were successfully industrialized. It is worth mentioning especially the Ce-doped silicates, aluminum perovskites and garnets, trivalent-ion-doped PbWO4 and the Cedoped binary rare earth halides, for recent reviews see [1-4]. The interest in new scintillator materials is pushed by the increasing number of new applications in medicine, industry or science, which require higher material performance. To optimize materials towards their intrinsic limits, understanding of energy transfer and storage processes, specific defects and their relation to the manufacturing technology appears of crucial importance [1,4]. The deep electron traps and their role in the afterglow of the Ce-doped silicates, shallow electron traps related to the antisite defects (Fig. 1) or the appearance of slower scintillation components and drop of light yield in the mixed Lu-rich aluminum perovskites and garnets are just a few examples of current questions in the field, which should be answered and the appropriate technological solutions found to improve the material performance. This presentation will review Figure 1: The LuAl antisite defect in Lu3Al5O12 structure. research activity and Resulting electron trap in the forbidden gap on the left. Emission understanding achieved so far at band within 300-350 nm due3+ to antisite defect and its the topics mentioned. competition with that of the Ce center in radioluminescence spectra at RT - upper left. Furthermore, the potential of new materials based on fast scintillation ceramics, superfast direct band-gap semiconductors or narrow-gap materials will be briefly discussed. * corresponding author e-mail: [email protected] References 1. M. Nikl, phys. Stat.sol. (a) 178, 595 (2000). 2. C.W.E. van Eijk, Nucl. Instr. Meth. Phys. Research A 460, 1 (2001). 3. K. W. Kramer, P. Dorenbos, H. U. Gudel, C. W. E. van Eijk, J. Mater. Chem. 16, 2773 (2006). 4. M. Nikl, Meas. Sci. Technol. 17, R37 (2006).

6

OB2

Atomistic simulation of defects in wide band gap scintillators C.R. Staneka*, K.J. McClellana, B.P. Uberuagaa, M.R. Levyb and R.W. Grimesb a

Los Alamos National Laboratory, Los Alamos, NM 87545, USA b Imperial College London, London, SW7 2BP, UK

Atomic scale simulations have been employed to investigate non-intuitive defect structure in a range of wide band gap scintillators, including: RE2O3 bixbyites, REAlO3 perovskites and RE3Al5O12 garnets (where RE generally denotes a rare earth cation from Lu3+ to La3+). By considering a range of compounds, we are readily able to determine compositional trends in defect related phenomena. The aim of these particular studies is to provide atomic scale detail of defect structure to compliment the interpretation experimental characterization data. However, our overall goal is to improve the performance of scintillators by fundamentally addressing the issue of defects.

Figure 1: The two unique cation sites of RE2O3 bixbyite, namely: the 8b with S6 symmetry (left) and the 24d with C2 symmetry (right), where dark spheres represent RE cations, light spheres denote oxygen and the cubes represent unoccupied oxygen positions.

Specifically, we will discuss the site preference of 3+ cations in RE2O3 bixbyite oxides. In the bixbyite structure, there are two crystallographically distinct sites, the so-called 8b and 24d sites, see Fig. 1. These sites have different symmetries, which leads to different optical properties of the activator cation residing on either site. For some combinations, e.g. the promising scintillator detector material Eu:Lu2O3, it is desirable to have all activator cations preferentially residing on one of these two sites (24d in the case of Eu:Lu2O3). We will present the results of calculations that predict the site preference of over 250 combinations of activator and host lattice. We will also discuss effects of 2+ and 4+ cation doping in perovskites and garnets as well as well as the effect of Gd substitution for Al on the defect structure of RE3Al5O12 garnets. * corresponding author e-mail: [email protected]

7

OB3

Data-driven exploration of the ionization-phonon partitioning in scintillating radiation detector materials Kim F. Ferrisa*, Bobbie-Jo Webb-Robertsona, David V. Jordana, and Dumont M. Jonesb* a

Pacific Northwest National Laboratory, P.O. Box 999,MS K6-08, Richland, WA 99352 USA b Proximate Technologies, LLC., Columbus, OH 43209 USA

The efficiency of scintillating radiation detection materials can be viewed as the product of a consecutive series of electronic processes (energy conversion, transfer, and luminescence) as outlined by Lempicki and others [1,2]. Using an approach proposed by van Roosbroeck and Robbins [3,4], the energy loss ratio (K) can be related to the conversion efficiency. As a first step in understanding the fundamental limits on scintillating materials, we have undertaken a data-driven approach to assessing the fundamental limits to the energy loss ratio, defined as the ratio of vibrational energy loss via optical phonons to ionization energy loss. Relevant data are relatively sparse, but sufficient for the development of materials signatures through forward mappings. The materials signatures for the physical properties in the Lempicki model have been used as a basis to explore the limits of K with chemical composition. While the coupling of ionization is strongly related to the optical phonon modes, both dielectric and band gap contributions cannot be ignored. When applied within a candidate screen, the resulting model for K imposes design rules—simple structural restrictions—on scintillating radiation detector materials. The Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the US Department of Energy under contract DE-AC06-76-RL1830. The authors gratefully acknowledge financial support from the PNNL Laboratory Directed Research and Development Project. * Corresponding author e-mail: [email protected] References 1. Lempicki, A.J. Wojtowicz, and E. Berman, Nucl. Instr. And Meth. A333, 304 (1993). 2. M.J. Weber, J.Lumin. 100, 35 (2002). 3. D.J. Robbins, J. Electrochem. Soc. 127, 2694 (1980). 4. W. van Roosbroeck, Phys. Rev. A139, 1702 (1965).

8

OB4

Scintillation response of Ce-doped garnets, perovskites and silicates under α, β and γ radiation Jiri A. Maresa*, Martin Niklb, Eva Mihokovaa, Alena Beitlerovaa, Anna Veddab, Carmelo D’Ambrosioc a

Institute of Physics, AS CR v.v.i., Cukrovarnicka 10, Prague 6, 162 53, Czech Republic b Dipartimento di Scienza dei Materiali dell’ Universita di Milano “Bicocca” and CNISM, Via Cozzi 53 , Milano, 20 125, Italy c PH-DT2 group, CERN, Geneva 23, CH 1211, Switzerland

The Ce-doped scintillators have reached high level of perfection and efficiency and are used in various applications [1]. Recently, new class of high light yield (L.Y.) Ce-doped halide crystals was prepared. For instance LaBr3:Ce has L.Y. ~ 61000 ph/MeV [2]. However, these materials are strongly hygroscopic and must be placed into humiditytight protective boxes. Other Ce-doped inorganic crystals as Y or Lu silicates, garnets or perovskites are non-hygroscopic, chemically and mechanically stable [3-5]. Among them the highest L.Y. is obtained in LSO:Ce, ~ 30000 ph/MeV [3,4]. In comparison with Cedoped Y or Lu garnets and perovskites [5] the LSO:Ce crystal shows often higher afterglow. The origin of this unwanted effect is not explained in the detail, but it seems to be related to electron trapping in deep oxygen-vacancy containing traps [4,6,7]. The main goal of this paper is to summarize basic scintillation properties of Ce-doped Y or Lu garnets, perovskites and silicates and provide their mutual comparison. Scintillation response (photoelectron or light yield, energy resolution non-proportionality etc.) of the crystals was measured using an advanced set-up based on HPMT [5] under excitation by γ-radiation (in the energy range 5 keV – 2 MeV) and also by α- and β-radiation (in the range around 5 MeV or tens of keV, respectively) using suitable radioisotopes. The αsources allow to excite thin surface layers of crystals or thin (units-tens of μm) scintillation films. Moreover, electrons from β- radioisotopes can influence (occupy) traps in crystals especially in LSO:Ce. The results of scintillation response studies of these Cedoped crystals will be confronted with their thermoluminescence characteristics. * corresponding author e-mail: [email protected] References 1. C.L. Melcher, NIM Phys. Res. A 537, 6 (2005). 2. E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, Appl. Phys. Lett. 79, 1573 (2001). 3. P. Dorenbos, J.T.M. de Haas, C.W.E. van Eijk et al., IEEE Trans. Nucl. Sci. 41, 735 (1994). 4. M. Kapusta, P. Szupryczynski, C.L. Melcher et al., IEEE Tran. Nucl. Sci. 52, 1098 (2005). 5. J.A. Mares, M. Nikl, A. Beitlerova, N. Solovieva, C. D’Ambrosio et al., NIM Phys. Res. A 537, 271 (2005). 6. J.G. Rogers, C.J. Batty, IEEE Trans. Nucl. Sci. 47, 438 (2000). 7. R. Visser, C.L. Melcher, J.S. Schweitzer et al., IEEE Trans. Nucl. Sci 41, 689 (1994).

9

OB5

Point defects as a limiting factor for Ce3+ emission A. Gektin, N. Shiran*, S. Neicheva, V. Nesterkina, V. Voronova Institute for Scintillation Materials, NAS of Ukraine, 60 Lenin Avenue, 61 001 Kharkov, Ukraine

The scintillation yield of fluoride crystals is not usually higher than 2000 Ph/MeV, i.e. it constitutes 2 to 3% of the most effective scintillators. At the same time, theoretical evaluations, based on taking into consideration the wide gap (Eg > 10eV), de-limit those values to 40-50% of the light emission yield. In this way, major efficiency losses in the doped fluorides have to do with the stage of energy transfer to Се3+ centers. The present research tackles an analysis of the importance of point defects for the structure proper of the Се3+ center, its closest ambience, as related to charge compensation and elastic stresses round the center, color centers formation and carrier transfer between the defects. The simple fluorides (LiF, СаF2, BaF2 , etc.), binary fluorides (LiBaF3, BaMgF4, KMgF3, LiYF4, LiLuF4, etc.) and ternary compounds (LiCaAlF6 and LiSrAlF6) are considered here as characteristic instances, demonstrating the tendencies in defect-formation during the transition from the cubic and fluorite lattices to the perovskites and more complex structures (colquiriites and elpasolites). During transition from simple to more complex compounds, not only the number of defects increases, but is the diversity of defect’ structures rises also. Besides the Schottky and Frenkel defects, antisites and stable interstitial fluorine ions appear, as well. More diverse becomes the structure of the Се3+ centers themselves. In particular, in various configurations observable are centers of the type CeBa3+, CeBa3+vLi −, CeBa3+ LiCa+, CeCa3+Fi −. The pre-dominant nature of the center structure determines as well the prevailing scintillation mechanism: direct excitation of Ce3+ ions by secondary electrons or X-rays, Ce3+ ions ionization by the capture of electrons and formation of Ce bound excitons and energy transfer from the electron-lattice excitation to Ce3+ ions. On the other hand, the capture of carriers brings about the color centers formation (and the appropriate reabsorption), redox reactions and similar energy dissipation at the transfer stage, too. Quite evident is the fact that, as the lattice becomes more complex and the number of dissipation channels increase, the radiation resistance of material becomes lower. Multiplication of those types of energy loss would act to worsen the luminescence efficiency in multicomponent fluoride compounds. * corresponding author e-mail:

10

OC1

Scintillator non-proportionality William W. Moses Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA

One of the fundamental properties of scintillators is the scintillation efficiency, or the conversion factor between the energy deposited and the number of visible photons produced. While often assumed to be a constant, it depends on both the energy and species of the ionizing radiation (gamma, alpha, beta, proton, etc.). These deviations from a constant are known as non-proportionality, and have been studied both experimentally and theoretically for ~50 years. The earliest studies centered on differences on particle type—why alpha and beta particles of the same energy produce a significantly different number of scintillation photons in the same material. Researchers during this period discovered a strong correlation between the scintillation efficiency and the ionization density, but the details of this relationship and its dependence on the material remained elusive, and interest in the field died out by the late 1960’s. Interest in the field was rekindled by the discovery of LSO scintillator in the 1990’s. The energy resolution of LSO (when excited by gamma radiation) is far worse than what is predicted by counting statistics, and the root cause was felt to be non-proportionality. Many different combinations of Auger electrons and fluorescent x-rays can be created after the primary interaction, and the scintillation efficiency for these low-energy secondaries is different than for the primary particles. A major advance at this time was the development of the Compton Coincidence technique for measuring the electron response (the scintillation efficiency as a function of energy for electrons), which greatly improved the accuracy of the measurement at low deposited energy. Work in this area has attracted greater interest recently. Several groups are constructing second-generation Compton Coincidence apparatus with significantly higher throughput and measurements from these instruments are just starting to appear. However, there is much left to be done. First, the electron response from significantly more samples must be measured. For most scintillation materials, only a single sample has been characterized, and it is not clear that the measurement accurately represents the material. The link between the electron response and the energy resolution for gamma rays is incompletely understood. In general, the energy resolution as a function of (gamma ray) energy cannot be predicted even if the electron response is known. Finally, there is no predictive theory for non-proportionality. We do not know what physical properties of a material (such as dopant concentration, crystal structure, defect concentration, etc.) contribute to the non-proportionality, nor why the shape of the electron response for the alkali halides is much different than that for oxides or the rare-earth halides. This paper summarizes this work and future challenges. This work is supported by the National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation, Office of Nuclear Nonproliferation Research and Engineering (NA-22) of the U.S. Department of Energy under contract No. DE-AC0376SF00098, grant number NNSA LB06-316-PD05 / NN2001000. * corresponding author e-mail: [email protected]

11

OC2

Energy resolution of scintillation detectors – new observations M. Moszyński*, A. Nassalski, A. Syntfeld-Każuch, Ł. Świderski Soltan Institute for Nuclear Studies, PL 05-400 Otwock-Świerk, Poland

According to the present knowledge, the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution. However, several observations collected in the last years on the influence of slow components of the light pulses on energy resolution suggest more complex processes in the scintillators. This was done with CsI(Tl) [1], ZnSe(Te), undoped NaI at liquid nitrogen temperature [2] and finally for NaI(Tl) at reduced temperatures below 0 °C. A common conclusion of these observations is the fact that the highest energy resolution, and particularly the intrinsic resolution, measured with scintillators, characterized by two components of the light pulse decay, is obtainable when the spectrometry equipment integrates the whole light of both components. In the limiting case, the afterglow could be considered also as a very slow component, which degrades the energy resolution. The recent study of LGSO, with its strong afterglow seems to suggest the above effect. Fig. 1 presents the most spectacular observation done on undoped NaI crystal at liquid nitrogen temperature.

Fig. 1. Left: Energy spectrum of 662 keV γ-rays measured in undoped NaI crystal at 50 μs integration time. Right: dependence of energy resolution and its components on the peaking (integration) time. Upper panel presents the number of e-h pair versus the peaking time, following [2].

The aim of this work is to summarize all above observations and to present them to the community hoping for a very interesting discussion. *corresponding author e-mail: [email protected] References 1. M. Moszyński, et al, IEEE Trans. Nucl. Sci., vol. 46, no. 4, pp. 880-885, Aug. 1999. 2. M. Moszyński, et al. Nucl. Instrum. Meth,. A., vol. A505, no. 1-2, pp. 63-67, June 2003.

12

OC3

From luminescence nonlinearity to scintillation nonproportionality A.N.Vasil’ev* Physics Faculty, Moscow Lomonosov University, 119992, Moscow, Russia

Luminescence excitation in the fundamental absorption region is well-known to be a nonlinear process since recombination of electrons and holes has features of either bimolecular or monomolecular processes. A finite fraction of correlated electrons and holes, which are created either directly by the excitation photon or as secondary excitations after inelastic electron-electron scattering, forms an exciton or recombines at a center in a monomolecular reaction. This fraction decreases with the increase of the spatial separation between a thermalized electron and a hole, which in turn increases with the total energy of the pair. The rest electrons and holes recombine via bimolecular process. Therefore luminescence excited through creation of electrons and holes is principally non-linear process. Additional non-linearity is due to numerous interactions depending on the local density of electronic excitations. The origin of important scintillator characteristics (yield, razing and decay time, non-exponential decay, afterglow, etc.) is naturally connected with the same mono- and bimolecular processes. The range of intensities for this non-linearity is extremely wide. This nonlinearity of luminescence often is not taken into account. For instance, we have to emphasize that one of the techniques typically used to study luminescence excitation in the fundamental absorption region – luminescence excitation spectroscopy – assumes that luminescence is a linear process (the yield is just a ratio of the emission and excitation photon fluxes). Some cases of nonlinearity of PWO green emission under VUV and X-ray excitation are discussed in the presentation. One way of simultaneous creation of electronic excitations with high density, which simulates the conditions within the track of ionizing particle, is to use femtosecond VUV laser pulses; these results are presented elsewhere. Track region created by an ionizing particle has a complicated structure. The simulation of this track can be performed using Monte-Carlo technique. This simulation needs detailed description of elementary processes such as electron-electron scattering with production of secondary excitations. We use polarization approximation, which regards this scattering as emission of different types of photons with account for the polarization of the media. A model which approximately expresses the dielectric permittivity for photons with non-zero wave-vector ε 2 (ω , k ) in terms of ε 2 (ω , 0 ) is proposed. The conditions, when the track structure can be described in terms of distribution of concentrations of excitations, are discussed. In this case the yield and the decay of scintillation can be obtained using the averaging of the luminescent data over distribution of concentrations. This distribution depends on the initial energy of an ionizing particle, and therefore the scintillation non-proportionality can be directly expressed in terms of luminescence non-linearity. * corresponding author e-mail: [email protected]

13

OC4

Kinetic Monte Carlo model of scintillation mechanisms in activated alkali halides and evaluation of their contribution to nonlinear response Sebastien Kerisit*, Kevin M. Rosso, and Bret D. Cannon Pacific Northwest National Laboratory, Richland, WA 99354

Light Intensity (arb. units)

Many radiation detection materials[1] have been shown to exhibit a nonlinear light output response as a function of the incident energy of gamma-ray radiation, a phenomenon that greatly contributes to the degradation of the energy resolution of these materials. However, mechanisms giving rise to nonlinearity remain unknown. A possible cause of nonlinearity is the incident energy dependence of the density of information carriers along the ionization track through its effect on modifying transport and recombination dynamics. To evaluate this hypothesis, we implemented a kinetic Monte Carlo (KMC) program and performed atomistic simulations of the collective dynamics of thermalized information carriers on realistic lattices. Our model aims to incorporate not only the kinetics but also the 1.E-03 efficiency of energy transport KMC model Hamada et al. (2001) processes. 1.E-04 The KMC model is based on the three-process model, introduced 1.E-05 by Dietrich and Murray[2], and also includes a range of additional 1.E-06 processes that may be turned ‘on’ and ‘off’ such as exciton diffusion and 1.E-07 trapping of information carriers at 0 2500 5000 7500 10000 12500 15000 defect sites, which have been Time (ns) identified in the literature as relevant Figure 1: Comparison of calculated and experimental processes. We initially focused on scintillation decay curves of CsI(Tl) ([Tl+]=0.1 mol%). activated alkali halide scintillators and have reproduced the scintillation decay curves of CsI(Tl) reported by Hamada et al.[3] for several activator concentrations (e.g. Figure 1). Our model also predicts a thallium concentration at which the intrinsic CsI emission should appear in the emission spectrum in accord with experimental observations. Finally, we can evaluate the contribution of processes such as non-radiative decay at defects and exciton-exciton annihilation to the nonlinear energy response of these materials. The authors acknowledge support from the Radiation Detection Material Discovery Initiative at PNNL. * Corresponding author e-mail: [email protected] References 1. J.E. Jaffe, D.V. Jordan, A.J. Peurrung, Nucl. Instr. and Meth. A 570, 72 (2007). 2. H.B. Dietrich and R.B. Murray, J. Lumin. 5, 155 (1972). 3. M.H. Hamada, F.E. Costa, M.C.C. Pereira, S. Kubota, IEEE Trans. Nucl. Sci. 48, 1148 (2001).

14

OC5

Non-proportionality of organic scintillators and BGO A. Nassalski*, M. Moszyński, A. Syntfeld-Każuch, Ł. Świderski, The Soltan Institute for Nuclear Studies, PL 05-400 Otwock-Świerk,Poland

According to the present knowledge the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution [1]. In this respect, the non-proportional response of organic scintillators was studied in comparison to that of a BGO crystal [2]. The studies covered tests of the BC408 plastic and the BC501A liquid scintillator in comparison to the response of an anthracene organic crystal. We put the question whether we will observe the influence of much lower density of the organic scintillators on their non-proportionality? The non-proportionality curve of BGO was used for the comparison, and according to [2] represents the fundamental characteristics of heavy oxide crystal material. Fig. 1 presents the comparison of the curves measured with the BC408 plastic, the BC501A liquid scintillator and the anthracene (left panel) to that of BGO crystal (right panel) [2].

Non-proportionality

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BGO Anthracene

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100

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100

1000

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Fig. 1 The non-proportionality curves of the BC408 plastic, the BC501A liquid scintillator and the anthracene (left panel) and the BGO crystal (right panel), following ref. [2].

The curves for the plastic and the anthracene used photopeaks up to 122 keV and afterwards the position of the Compton edges. We find interesting the observation that the response of anthracene to gamma rays is proportional above 1 MeV while in the case of inorganic scintillators it is observed above 100 keV. * corresponding author e-mail: [email protected] References 1. M. Moszyński, SPIE Proceedings, Vol. 5922, 592205-1. 2. M. Moszyński, M. Balcerzyk, W. Czarnacki, M. Kapusta, W. Klamra, A. Syntfeld, and M. Szawlowski, „Intrinsic energy resolution and light field nonproportionality of BGO”, IEEE Trans. Nucl. Sci., vol. 51, no. 3, pp. 1074-1079, June 2004.

15

0.6

PMo01

Production and development of scintillation materials at Bogoroditsk Technical Chemical Plant A.Baberdina , I.Korneevb, M.Korzhikc a

Bogoroditsk Technical Chemical Plant, 4 Vayzovskiy, , Bogoroditsk, 301801 , Russia b JSC Russian Electronics, 9 Tverskaya bldg 7 , Moscow, 125009 , Russia c Institute for Nuclear Problems, 11 Bobruiskaya, Minsk, 220030, Belarus

In this report we describe the world largest production capacity to grow scintillation crystals on a base of oxide compounds. The contribution of the Bogoroditsk Technical Chemical Plant (BTCP) to deliver scintillation crystals for LHC program at CERN will be revived. New developments on a base of tungstates, molibdates, silicates and aluminates and their possible applications will be discussed. * corresponding author e-mail: [email protected]

16

PMo02

Position resolution in LaBr3 scintillators using multi-anode photomultiplier tubes Peter F. Bloser*, Mark L. McConnell, John R. Macri, James M. Ryan, M. V. Amaresh Kumar University of New Hampshire, Space Science Center, 39 College Road, Durham, NH, 03824, USA

Advanced scintillator materials such as LaBr3:Ce hold great promise for future hard Xray and gamma-ray astrophysics missions due to their high density, high light output, good linearity, and fast decay times. Of particular importance for future imaging instruments, such as coded-aperture telescopes and Compton telescopes, is the precise spatial location of individual gamma-ray interactions. We have investigated the position resolution achievable within monolithic (5 cm × 5 cm × 1 cm) LaBr3:Ce crystals optically coupled to multi-anode photomultiplier tubes to form compact Anger cameras. We present results for the position and energy resolution over the entire detector volume using these devices and discuss their applicability to future imaging astrophysics missions. * corresponding author e-mail: [email protected]

17

PMo03

Measurement of photomultiplier gain using LYSO afterglow D. Brasse*, S. Salvador and J.-L. Guyonnet Institut Pluridisciplinaire Hubert Curien, CNRS/IN2P3 and ULP 23 rue du Loess, Strasbourg, 67037, France

Most of the nuclear medical imaging devices are based on scintillating crystals coupled to photomultipliers tubes (PMT). For research and development systems, the measurement of the light yield in absolute units is off importance. An absolute calibration is then required to measure the energy released in the crystal in terms of the number of photoelectrons emitted from the photocathode. The precise knowledge of the photomultiplier gain is then mandatory. In most of the case, a pulsed source of light is used to produce a flux of optical photons incident on the PMT photocathode and generating photoelectons via the photoelectric effect. The flux of photons is optimized to maximize the single photoelectron probability. The PMT gain is then calculated by fitting the resulting output spectrum using a method such the one described by Bellamy et al [1]. The photoemission of the photocathode can also be used as a photoelectron source with the disadvantage of a poor production rate. In this work, we propose to use the afterglow of the Lutetium Yttrium Orthosilicate cristal (LYSO: Lu1.8Y0.2SiO5:Ce) as a source of light. The key points of this method are: a) a “free” high rate single photoelectron generator, b) the easiness to scale the method to multi anode PMT and, (c) the possibility to perform the calibration “on board” (i.e. imaging system using crystals with afterglow). The method has already been applied on two H3164-10 PMTs from Hamamatsu Corp. A light guide of 1.5x1.5 mm² was used for the pulsed source method and a LYSO crystal with similar size was used for the proposed method. For a high voltage equal to -1250 V, the PMT gains are 6.1 106 and 5.7 106 for the two PMTs measured with the LYSO method compared to 6.8 106 and 5.7 106 measured with the pulsed source method. Similar results will also be presented for multianode PMTs. * corresponding author e-mail: [email protected] References 1. E.H. Bellamy et al Absolute calibration and monitoring of a spectrometric channel using a photomultiplier, NIM A 339, 468-476 (1994)

18

PMo04

Pixelated scintillator for x-ray imager and its effect on light output and spatial resolution Bo Kyung Cha, Byoung-Jik Kim, Chae-hun Lee, Jun Hyung Bae, Hyunduk Kim, and Gyuseong Cho* Dept. of Nuclear and Quantum Eng., Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea

Pixelated-scintillator films to be used for X-ray image sensors were developed and their preliminary test was performed. The air gap between each scintillator pixel reduces the transport of visible light photons generated by x-ray into the neighboring pixels so it will maximize the overall spatial resolution as well as the light collection efficiency of an Xray imager. For further improvement the interpixel gaps are filled with a reflective or a lower refractive material than CsI(Tl) scintillator.[1] The scintillator films of 50 μm thick were made with thallium doped CsI by the conventional physical vapor deposition process on glass substrates with a patterned photoresist layer by UV lithography. [2] Fig. 1 shows the microstructures of a pixelated CsI (Tl) scintillator film with a pitch of 50 μm. In this work, the pixelation effects on light collection efficiency and spatial resolution of the scintillator layer were evaluated by a CCD sensor and X-ray with the medical diagnostic energy range. The relative light output and the spatial resolution have improved 10~20% in the preliminary test as shown fig. 2. Also various materials such as Al, SiO2, and TiO2 etc. have been filled by chemical vapor deposition (CVD) or atomic layer deposition (ALD) in the gap of pixelated scintillator and their effects on the light collection efficiency and the spatial resolution of the scintillator layer were studied. 800

Light Ouput(Arb.units)

700 CsI(Tl) scintillator film CsI(Tl) scintillator film with SiO2coating

600 500 400 300 200 100

Fig. 1 SEM micrographs of a pixelated CsI(Tl) scintillator

0

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600

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Wavelength(nm)

Fig. 2 Measured light output of CsI(Tl) scintillator before and after SiO2 coating

* Corresponding author e-mail: [email protected]

References 1. Recent advances in columnar CsI(Tl) scintillator screen, proceedings of SPIE Vol. 5923(2005) 2. A study on spatial resolution of pixelated CsI(Tl) scintillator, NIM. A(2006), accepted

19

PMo05

Measurements of x-ray imaging performance of granular phosphors Min Kook Choa, Seung Man Youna, Chang Hwy Lima, Ho Kyung Kima*, Hyosung Chob, Jung-Min Kimc a

School of Mechanical Engineering, Pusan National University, Busan 609-735, Republic of Korea b Department of Radiological Science, Yonsei University, Wonju 220-710, Republic of Korea c College of Health Sciences, Korea University, Seoul 136-703, Republic of Korea

Although thallium-doped cesium iodide (CsI:Tl) is more appropriate to digital radiography because of the better spectral matching to a readout pixel array and the less light spreading, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) granular phosphor screen is still popular in diagnostic radiology owing to its well-known technology and easy handling in size, thickness, and flexibility.[1] For a wide range of coverages (34 – 135 mg/cm2), we have investigated the fundamental imaging performance of Gd2O2S:Tb phosphors in terms of modulation-transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE). As an optical photon readout elements, CMOS photodiode array having a format of 512 × 1024 pixels with a pitch of 48 μm was used. For a representative radiation quality, RQA 5, suggested by IEC (International Electrotechnical Commission, Report 1267), the presampled MTFs were measured using a slated-slit method to avoid aliasing and the NPSs were determined by 2D Fourier analysis of white images. The DQEs were assessed from the measured MTF, NPS and the estimated photon fluence. The fluence was estimated using the experimentally measured exposure and the computational program for x-ray spectral analysis. Figure 1(a), (b) and (c) show the examples of the measured MTF, NPS and DQE, respectively. In this work, we report the experimental results of x-ray imaging performance of Gd2O2S:Tb granular phosphors with various thicknesses. This study will be useful for the selection guidance of Gd2O2S:Tb phosphors for the relevant imaging tasks.

Figure 1: Examples of imaging performances of a granular phosphor when coupled to CMOS photodiode array: (a) MTF, (b) normalized NPS, and (c) DQE. All measurements were performed by X-rays operated at 45 kVp and tailored by 0.5 mm thick Al.

This work was supported by Grant No. R01-2006-000-10233-0 from the Basic Research Program of the Korea Science & Engineering Foundation. * corresponding author e-mail: [email protected] References 1. J.-M. Kim, H. K. Kim, M. H. Cheng, M. K. Cho, C.-S. Shon and C. H. Lim, Key Eng. Mater. 321-323, 1056 (2006).

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PMo06

Performance of a facility for measuring scintillator non-proportionality Woon-Seng Choonga*, Guilia Hullb, William W. Mosesa, Kai M. Vetterb, Stephen A. Payneb, Nerine J. Cherepyb, and John D. Valentineb a

Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 95720, USA Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551, USA

b

We report on the performance of the recently constructed instrument to characterize the light yield non-proportionality of scintillating materials. The instrument is located at LLNL and uses the Compton Coincidence Technique developed by Valentine and Rooney [1]. We have constructed a high throughput version known as the SLYNCI (Scintillator Light Yield Non-proportionality Characterization Instrument), which has a much higher data collection rate than the original instrument. A collimated 1 mCi 137Cs source illuminates the scintillator sample from a distance of about 17.5 cm and a total of 5 high-purity germanium detectors (21%−34%) placed ~10 cm from the scintillator measure the energy of the scattered gamma ray. The source-collimator can be placed in either of two scattering positions spaced 15 degrees apart, allowing nearly uniform scattering angle coverage from 0 to 146 degrees, corresponding to energy deposits in the scintillator from 0 to 466 keV. While the scintillator is presently coupled to a photomultiplier tube (Hamamatsu R6231), it will eventually be coupled to a hybrid photodetector (DEP PP0475B), which has extremely linear response. The output of each HPGe and the PMT is digitized with a free-running 12-bit, 100 MHz ADC (SIS 3300). We measure the performance of the SLYNCI using a NaI:Tl scintillator (1 cm diameter and 1 cm high cylinder). The total coincidence rate is about 40 cps and 80 cps with a 3 mm and 5 mm collimator hole diameter respectively. A preliminary measurement of the relative light yield versus the electron energy at the two source-collimator positions is shown in Figure 1 and 2.

Figure 1: Light yield responses for NaI:Tl with source-collimator at the first position

Figure 2: Light yield responses for NaI:Tl with the source-collimator at the second position

This work was supported by the National Nuclear Security Administration (NA-22). * corresponding author e-mail: [email protected] References 1. J. D. Valentine and B. D. Rooney, NIM, A353, 37 (1994).

21

PMo07

Advances in yield calibration of scintillators J.T.M. de Haas*, P. Dorenbos Delft University of Technology, Faculty of Applied Sciences, Mekelweg 15,2629 JB Delft,The Netherlands

Determination of the absolute scintillation yield remains an ongoing issue in scintillator research. New types of scintillators, new types of photon sensors but also new insights in the methods to perform calibrations initiate new studies in this field. In this work, by means of a photomultiplier tube (PMT), a Si-photodiode (PD), and a Si-avalanche photodiode (APD), the absolute light yield of recently developed LaBr3:Ce, LaCl3:Ce and LYSO:Ce scintillators and traditional Lu2SiO5:Ce, Bi4Ge3O12, NaI:Tl CsI:Tl and CsI:Na scintillators were determined. These are all well known scintillators that cover emission wavelengths from 350 nm to 560 nm. Different scintillator packaging methods were used, and scintillator mounting was with or without optical coupling to the photon detector. The new advances in the calibration method are; 1) proper corrections for the reflectivity of the photon detector, 2) correction for photon losses in the few nm thick Si-dead layer in PDs and APDs, 3) proper method of gain calibration of PMTs. The values of the absolute scintillation yield measured with the three different photon detectors are in good agreement with each other.

6

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Figure 1: Emission of 1) CsI:Tl, 2) LaBr3:Ce, 3) NaI:Tl, 4) CsI:Tl, and 5) the PMT quantum efficiency curve, and 6) the transmission of 5 nm Si. * corresponding author e-mail: [email protected]

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PMo08

Small size CsI(Tl) spectrometry efficiency and properties dependence on temperature Eli Doleva,b, Avi Manor a,b, Irad Brandysb, Danny Tiroshb, Gennady Ziskinda and Itzhak Oriona* a

Ben-Gurion University of the Negev, POB 653, Beer-Sheva, 84105, Israel b NRCN, POB 9001, Beer-Sheva, Israel

Small-sized radiation scintillator detectors have been extensively developed for portable radiation survey systems for variety of applications. Their ability to identify the energylines of a gamma-radiation source makes these detectors suitable for personal detection. Additional advantages of these detectors are their miniature electronics and operation at room temperature. However, while operating these detectors, it is essential to inspect their efficiency, sensitivity, and stability under the practical range of the environmental conditions for their operation. The aim of our research was to study the changes in CsI(Tl) detector response (19 mm diameter X 41.3 mm length), in a full range of operation temperatures, from -25 to 60 centigrade. The results showed that the photopeak efficiency for the Cs-137 gamma-line remained constant, although the peak centre channel was shifted as function of the detector temperature. The peak spectral resolution was also analyzed in the same temperature range and was found to be stable around 8%. 90

CsI(Tl) 19 x 41.3 mm

Peak Area (cps)

80

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Figure 1: CsI(Tl) photopeak net area counts measured at 661 keV with versus temperature.

Since the photopeak efficiency is constant over the whole tested temperature range, the CsI(Tl) detector is a suitable spectroscopy detector for environmental operations. * corresponding author e-mail: [email protected]

23

PMo09

Generation of defects in inorganic scintillators under small dose rate irradiation E.Auffray-Hillemansa, A.Borisevichb, V.Dormenevb*, G.Drobychevb, M.Korzhikb, P.Lecoqa a

b

CERN, Geneva, 1211, Switzerland Institute for Nuclear Problems, 11 Bobruiskaya, Minsk, 220050, Belarus

The long term stability of the inorganic scintillation material parameters in a radiation environment is a crucial feature to carry on precise measurement of ionizing radiation. However, single crystalline materials contain a priori different kind of defects which form traps with a wide distribution of energy levels in forbidden band. The influence of shallow traps with energy levels in the vicinity of the bottom of the conduction band or the top of the valence band is considered to be negligible to contribute to the quasistationary optical transmission damage of crystal under ionizing radiation. This assumption is based on the fact that shallow capturing centers also create under irradiation shallow electron or hole centers decaying in a very short time at room temperature. They contribute to transient induced absorption bands at relatively high irradiation dose rate. Under a continuous steady state irradiation of the crystal even at low dose rate a new mechanism of the radiation damage is observed. This mechanism is related to the aggregation of anion vacancies stimulated by irradiation. The probability of coalescing these defects in pairs and more complex defects with diffusion is significantly increased by the interaction of uncharged and neutralized vacancies. Pairs have deeper capture levels in compared to single vacancies and can create meta-stable color centers increasing the optical absorption in the visible spectral region under ionizing radiation. This phenomenon leads to the suppression of the induced absorption dynamic saturation at moderate dose rates and to a slow and continuous decrease of the amount of scintillation light detected by photo detectors. The model of the new damage mechanism and experimental evidence of this pair creation effect under continuous irradiation of lead tungstate scintillation crystals will be discussed in this report. * corresponding author e-mail: [email protected]

24

PMo10

The antisite defect-related trap in YxLu1-xAlO3:Ce single crystals M. Fasolia*, I. Fontanaa, E. Mihokovab, M. Niklb, A. Veddaa, Y. Zorenkoc, V. Gorbenkoc a

Dip.Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy b Institute of Physics AS CR, Cukrovarnicka 10, 16253 Prague, Czech Republic c LOM, Department of Electronic Ivan Franko National University of Lviv, 79017 Lviv, Ukraine

Single crystals of YxLu1-xAlO3:Ce (0≤x≤1) aluminum perovskites belong to highly performing scintillator systems, which become increasingly employed in various applications, see [1,2] for review. Despite of high figure-of-merit of these materials, the nature of trapping states in the forbidden gap and their participation in the processes of energy transfer and storage during the scintillation conversion is not fully understood. Consequently, there is room for their optimization. Recently, the dominant shallow trapping state in Ce-doped aluminum garnets was determined using thermoluminescence [3-5] and taking advantage of the comparison between single crystal, optical ceramics and thin film materials. The antisite defect (Y or Lu ion at the Al octahedral site) appears as an electron trap situated a few tenths of eV below the conduction band. While this defect is present in high concentration in bulk single crystals grown from high temperature melt, it is practically absent in optical ceramics or thin single crystalline films (SCF) prepared by Liquid Phase Epitaxy due to significantly lower preparation temperatures [6]. An analogous antisite defect was detected also in the aluminum perovskite systems, evidenced by modifications of the exciton-related luminescence spectra and decay kinetics [7]. The aim of this presentation is to investigate the influence of the antisite defect on the optical properties of YAlO3:Ce and (Y-Lu) mixed perovskites in comparison with SCF analogs of these compounds and to provide quantitative characteristics of such a trap. The influence on the scintillator timing characteristics due to retrapping processes at such a trapping state during the energy transfer stage will be discussed. * corresponding author e-mail: [email protected] References 1. M. Nikl, phys. Stat.sol. (a) 178, 595 (2000) 2. C.W.E. van Eijk, Nucl. Instr. Meth. Phys. Research A 460, 1 (2001). 3. M. Nikl et al, phys. stat. sol. (b) 242, R119 (2005). 4. M. Nikl et al, J. Appl. Phys. 101, 033515 (2007). 5. E. Mihóková et al J. Lumin. (2007). doi:10.1016/j.jlumin.2006.05.004. In press. 6. Y. Zorenko et al, phys. stat. sol. (a) 202, 1113 (2005) 7. Zorenko, Y., et al., Radiat. Meas. (2007), doi: 10.1016/j.radmeas.2007.01.046. In press

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PMo11

On the energy resolution optimization of CsI(Tl) crystals for the R3B calorimeter M. Gascóna*, H. Alvarez-Pola, J. Benlliurea, E. Casarejos, D. Cortina, I. Durán, for the R3B collaboration a

GENP, Dept. Fisica de Particulas, Univ. Santiago de Compostela, 15782 Santiago de Compostela, Spain

A versatile, high resolution, high acceptance and high efficiency setup, has been proposed for the kinematically complete measurement of reactions induced by high-energy radioactive beams at FAIR[1] in Darmstadt, Germany. The experiment, named R3B [2], devises the construction of a calorimeter for the detection of gammas and charged particles originated in nuclear reactions from relativistic exotic beams. The main properties of this device, high total absorption efficiency (≥ 80% for γ’s at 15 MeV in the laboratory frame) and good angular resolution(≈ 1 deg for Θ ≈ 35 deg), are imposed by the very particular kinematics of energetic γ-rays (up to10 MeV in the CM system) emitted by sources moving with relativistic velocities and by the typically low intensities of the secondary beams involved. In order to ensure these nominal values in all the angular domain, the polar angular segmentation and the thickness of the scintillation material will be optimize for separate angular regions. All these considerations determine the choice of the device geometry. On the other hand, the intrinsic resolution of the scintillator material should be good. To guarantee the polar angle segment, we propose a detector divided into small frustum-like crystals (~ 5000 crystals with a average size 10x20x150 cm3) [3]. We will present in this paper, the energy resolution measurements of CsI(Tl) crystals with sizes varying from 1 to 20 cm. Square uniform cross-section and frustum-like pieces have been used. Different LAAPDs were compared. The energy resolution measurements were performed after optimization of the shaping, wrapping, optical coupling and surface treatment and APD stabilization (HV and temperature). The results obtained in terms of energy resolution after optimization are not so far from the Calorimeter requirements, at least in the less stringent angular region and seem to be the most plausible option for this part. * corresponding author e-mail: [email protected] References 1. FAIR. http://www.gsi.de/fair/index_e.html 2. R3B Technical proposal. FAIR-PAC/NUSTAR/R3B, January 2005. 3. GSI Scientific report 2006. www.gsi.de

26

PMo12

Scintillation properties of 1 inch Cs2LiYCl6:Ce crystals Jarek Glodo, W. M. Higgins, E. V. D. van Loef, and Kanai S. Shah Radiation Monitoring Devices, Watertown, MA 02472, USA

Cs2LiYCl6:Ce (CLYC) is one of the most interesting new scintillators, particularly for dual gamma – neutron and neutron detectors [1]. It has a unique property that allows one to easily distinguish between gamma and neutron induced signals based on the shape of a scintillation pulse (pulse shape discrimination). There are few materials that possess this property, but CLYC seems to excel. The properties of CLYC have been previously described elsewhere [1] but only for small crystals of a cubic centimeter or so. Typical results provide light output of about 20,000 photons per MeV (gamma) and 70,000 per neutron. Energy resolution was estimated to be 6-7% at 662 keV; that is comparable result to NaI:Tl or CsI:Tl, even though their light output is over twice as high.

25

intensity, counts/sec

Cs2LiYC6:Ce

662 keV

20 15

ΔE ~ 5.1%

10 5 137

Cs Spectrum

0

0

200

400

600

800

energy, keV

Figure 1: A picture of 1 inch CLYC crystal and a 137Cs energy spectrum recorded with this crystal.

Recently we have grown 1 inch diameter CLYC crystals that are more suitable for applications. Figure 1 (left) shows a picture of 1 inch diameter and 1 cm height sample. The sample provided excellent results. For example 5.1% energy resolution was measured at 662 keV. The light output was estimated to be ~20,000 photons/MeV (or about 4500 photoelectrons per MeV). The sample also exhibited excellent linearity that suggests a possibility for even better energy resolution with a superior detector (e.g. a new super/ultra bialkali photocathode based photomultiplier). The neutron peak was observed at about 3.2 MeV (gamma equivalent) and its resolution was 2.9%. A gamma – neutron discrimination was also achieved. * corresponding author e-mail: [email protected] References 1. C. M. Combes, P. Dorenbos, C. W. E van Eijk, K. W. Kramer, H. U. Gudel, J. Lumin. 82, 299-305 (1999)

27

PMo13

Luminescence properties of ZnO nanocrystals and ceramic L.Grigorjevaa*, D.Millersa, J.Grabisb, C.Montyc, A.Kalinkoa, K.Smitsa, V.Pankratova a

Institute of Solid State Physics, Universty of Latvia, Riga,LV-1063,Latvia Institute of Inorganic Chemistry, Riga Technical University, Salaspils, LV-2169, Latvia c CNRS Processe, Materials and Solar Energy Laboratory (PROMES), France

b

ZnOcrystal VC_com ceramic

1600

1200

x 0.1

50 nm TES

800

400

a

Luminescence intensity, a.u.

Luminescence intensity, a. u.

The results of luminescence excitation spectra, luminescence spectra and decay kinetics in ns time region were studied. Experiments were performed at the SUPERLUMI station at DESY, Hamburg. The photoluminescence excited by 266 nm laser (pulse duration 10 ns) was presented too. The ZnO and ZnO:Al nanopowders (NP) were prepared by vaporization-condensation (VC) in Solar furnace [1] from two different raw powders: commercial (Com) and obtained by plasma (PL) synthesis. The XRD, SEM and Raman spectra was used for powders characterization. In Fig.1a.the luminescence spectra of ZnO crystal, NP and ceramic are presented. The SEM image of VC-Com powder is shown.

ZnO_crystal VC_Com VC_Pl_1.9 Al

1000

b 100

8.5 K Lum.3.36 eV, Excit. 14 eV

10

0

10

20

30

t, ns

0 2,8

2,9

3,0

3,1

3,2

3,3

E, eV

3,4

Fig.1. Luminescence spectra (a) and decay kinetics (b) of ZnO.

The VC powders have whiskers type morphology with average diameter ~50 nm (Fig.1a, inset). Exciton -phonon as well as exciton-exciton interaction processes in bulk crystal, NP and ceramic are different. For example, the multiple-phonon processes and intensity in TES band region are more effective in NP (Fig.1a). The RT luminescence and decay in undoped and ZnO:Al NP was studied and compared with luminescence in bulk crystal. The luminescence due to exciton-exciton interaction depends on excitation density and was studied for different ZnO NP. Acknowledgment: the research was supported by DESY and the European Community by Contract RII3-CT-2004-506008 (IA-SFS) and Latvian Materials Research Program. corresponding author e-mail: [email protected] References 1. B.Martinez, F.Sandiumengue, L.Balcells, J.Arbiol, F.Sibieude, C.Monty, Phys.Rev.B. 77, 179 (2004)

28

PMo14

Spectroscopic studies of Ce3+ ions in lead fluoride U. Happeka* and J.A.Campbellb a

Dept. of Physics and Astronomy, The University of Georgia, Athens, GA, USA b Physics Department, Canterbury University, Christchurch, NewZealand

Lead fluoride is of interest as an optical material of high dispersion [1] and even more as a potential scintillator host: it is a transparent material of high density. However, attempts to activate PbF2 have failed [2]. Derenzo et al. [3] have used ab-initio quantum chemistry methods to demonstrate that cubic PbF2 cannot be an efficient scintillator due to trapped carriers, but this alone should not prohibit luminescence in activated materials. Here we report on precision measurements of the Ce3+ energy levels of Ce3+ in PbF2. Investigating low doped single crystals, the energy levels of isolated Ce3+ ions could be obtained. *

Corresponding author email: [email protected]

References 1. Jones, D.A., Jones, R.V. and Stephenson, R. W. H., Proc. Phys. Soc. B65(1952) 2. D.F. Anderson, J.A. Kierstad, P.Lecoq, S. Stoll and C.L. Woody; Nucl.Instr. Meth. A 342 473. 3. S.E. Derenzo, M.Klintenberg, M.J.Weber; IEEE Trans. Nucl. Sci. 46 (1999) 1969.

29

(1994)

PMo15

Design of an apparatus to measure optical reflectance of scintillating crystal surfaces Martin Janecek, William W. Moses Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA

Monte Carlo simulation is often used to predict and optimize the light collection in scintillation detectors. In order for the simulation to be accurate, the light reflectance off an internal surface within a scintillating crystal must be understood well. However, this distribution is poorly understood and so most models assume either purely specular or purely diffuse (Lambertian) reflections. We have designed an apparatus that will accurately measure the reflectance distribution within a scintillating crystal. A laser is aimed towards the center of a 2-inch diameter scintillating crystal hemisphere. The laser can be positioned at any arbitrary angle. The laser beam is reflected off the flat surface of the hemisphere and the light distribution is measured by a movable array of photodiodes that can measure the reflected light over the entire 2π solid angle. The laser is a 440-nm un-polarized TEM00 laser with 150 K, arises from the tunneling recombination process. Its contribution into the luminescence decay can be considerably reduced by the co-doping with some trivalent rare-earth ions, resulting in the decrease of the number of oxygen vacancies and the isolated lead vacancies in the crystal. This leads to the strong suppression of the slow (μs - ms) and the enhancement of the fast (2-4 ns at RT) luminescence decay components. Thus, the use of the crystal growth an annealing conditions and the co-doping with suitable trivalent rare-earth ions, which lead to the reduction of the number of oxygen and lead vacancies, can result in the considerable improvement of scintillation characteristics of lead tungstate crystals. *corresponding author e-mail: [email protected] References 1. M. Nikl, Phys. Stat. Sol. (a) 178, 595 (2000). 2. A. A. Annenkov, M. V. Korzhik, and P. Lecoq, Nucl. Instr. Meth. Phys. Res. A 490, 30 (2002).

67

OF2

Radiation hardness and recovery processes of PWO crystals at –25oC R. W. Novotnya*, S. F. Burachasd, W. Döringa, V. Dormenevb, Y. M. Goncharenkoc, M. S. Ippolitovd, A. Hofstaettere, M. Korzhikb, V. Mankod, Y. M. Melnickd, O. Missevitchb,V. V. Mochalovc, A. V. Ryazantsevc, P. A. Semenovc, G. Tamulaitisf, A. V. Uzunianc, A. A. Vasilievd, A. N. Vasilievc and for the PANDA collaboration a

II. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany b INP, Belarus State University, 11 Bobruiskaya, 220030 Minsk, Belarus c Institute for High Energy Physics, Pobeda 1, 142280 Protvino, Russia d RRC Kurchatov Institute, Kurchatov sq. 1, 123182 Moscow, Russia e I. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany f Vilnius University, Vilnius, Lithuania

The EM calorimeter of PANDA at the FAIR facility will rely on an operation of the PWO scintillators at temperatures near –25oC to provide sufficient resolution for photons in the energy range from 8GeV down to 10MeV. Investigations, performed for the first time at the radiation facility at IHEP (Protvino) have indicated a significantly different behavior in the time evolution of the damaging processes well below room temperature. The experiment controls the change of the optical transmission via the DC-measurement of the photomultiplier current generated by the light of blue or red LEDs as a function of the irradiation time and dose rate due to a strong 137Cs source. Fig. 1 illustrates the relative change of transmission via the PM current as a function of exposure time at two temperatures. The damage dominates recovery processes or even prevents saturation in contrast to the behavior at room temperatures, where dynamic equilibrium is reached.

Figure 1: PM output as a function of the irradiation time at a dose rate of 20rad/h.

The paper will discuss the results of the experimental program, which studies full size samples of all major suppliers, produced differently with respect to doping level or manufacturing processes. Temperature dependence of recovery processes will be described taking into account defect properties, TL- and EPR-data and influence of the creation of MoO 34− -centers at low concentration of molybdenum in the crystal, which decay in the region of the operating temperature and lead to a broad radiation induced metastable absorption band near 550nm. The results and conclusions might have a strong impact on the design and operation of the PANDA-EMC or ALICE-PHOS and further high resolution electromagnetic calorimeters based on PWO. * corresponding author e-mail: [email protected]

68

OF3

Transformations of absorption and emission centers in PbWO4 Pavel Bohacek*, Natalia Solovieva, Martin Nikl Institue of Physics AS CR, Na Slovance 2, 18221 Prague 8, Czech Republic

The model of absorption and emission centers in PbWO4 given in [1] is based on the vacancy, VWO3, which is formed after removing a molecule of WO3 from its place in PbWO4 crystal. From the complex ion [WO4]2- rests then in the place the ion O2-. According to the model the center VWO3 + O2- is responsible for absorption at 340 nm. When at oxidation annealing the center incorporates an interstitial oxygen atom, Oi, its structure changes to VWO3 + O2- + Oi, and its absorption is shifted to 430 nm. The third variant, VWO3 + VO, formed when the oxygen is led away, does not reveal any absorption in the wavelength range 320 – 1100 nm. Luminescence is connected with the other group of three centers, dominating in crystals with surplus of WO3. These centers contain, in addition, a vacancy of lead. The red emission is bound to the center VWO3 + VPb + O2- + Oi absorbing at 355 nm, the green emission G(I) is connected with the center VWO3 + VPb + O2- , which is absorbing at 330 nm, and the center VWO3 + VPb + VO is responsible for the other green emission, G(II), the intensity of which at RT is comparable with that of BGO. Annealing experiments in [1] were done at 600°C. In this paper transformations of the emission centers are followed at annealing in various atmospheres at the temperature of 930°C. The intensity of G(II) emission of samples of various stoichiometries annealed in Ar was, in general, increasing to its maximum and than decreasing. The time for reaching the maximum is increasing with increasing content of PbO in the crystal. A mechanism explaining this phenomenon is proposed. After reaching its maximum the G(II) intensity decreases steadily and after several hours it is near zero, even when at the annealing the absorption at 330 nm decreases (which means that new empty centers VWO3 + VPb + VO are formed). But the G(II) intensity is markedly increased, when the samples are rebrushed and re-polished. It follows that the emission G(II) is conditioned by presence of a stress around the center VWO3 + VPb + VO. Higher intensity of G(II) emission was found in a PWO crystal which was intentionally prepared with a higher inner stress in its volume. * corresponding author e-mail: [email protected] References 1. P. Bohacek, S. Zazubovich. N. Solovieva, M. Nikl, Opt. Mater. (2007), in press.

69

OF4

Scintillation mechanism in complex structure doped oxides and novel developments M.Korzhika a

Institute for Nuclear Problems, 11 Bobruiskaya, Minsk, 220030, Belarus

An efficiency of the final stage of luminescent center excitation mechanism in scintillator plays a major role to accomplish fast and bright scintillation materials. We focus our attention on complex oxide crystals doped with Ce3+ because the Ce3+ ion interconfiguration luminescence presumes the simultaneous presence of different excitation mechanisms. The charge transfer excitation mechanism of the doping ion luminescence naturally appears from the fact that heterovalent Ce ions have a high cross section for capturing holes. Another mechanism of scintillation, which is defined as energy transfer excitation mechanism, originates in crystals from sinsitizing of activator luminescence by intrinsic luminescence centers. Now numerous compounds of rare earth aluminates and silicates show high light yield scintillation due to combined contribution of both mechanisms. Here we discuss luminescence excitation mechanisms and scintillation properties of known and new Sn and Ge based materials doped with Ce. Sn and Ge ions allow to construct a variety of compounds which are isostructural to silicates. The factors which influence energy transfer efficiency in oxides also will be considered. * corresponding author e-mail: [email protected] References 1. Use the Physical Review reference format 2. A. N. Example, Journ. Nam. 53, 123456 (2007).

70

PTu01

Comparison of LaBr3:Ce, LaCl3:Ce, CZT and NaI(Tl) for resolution of nuclear material spectra Dimitri Alexieva*, Li Moa,b, and Michael Smitha,c a

Australian Nuclear Science and Technology Organisation (ANSTO), PMB1, Menai, NSW, Australia b Institute of Medical Physics, School of Physics,University of Sydney, NSW 2006, Australia c RSPhysSE, Australian National University, ACT 0200, Australia

Energy resolution and efficiency comparison were made of new scintillators, Lanthanum Bromide (LaBr3:Ce), Lanthanum Chloride (LaCl3:Ce), with Cadmium Zinc Telluride (CdZnTe or CZT) and Sodium Iodide (NaI(Tl). The experiments conducted have shown that LaBr3:Ce, and LaCl3:Ce scintillator crystal provided by Saint-Gobain have adequate resolution and efficiency for measurement of spectral response in the region of 150 keV to 450 keV. An overall advantage in energy resolution and efficiency of LaBr3:Ce and LaCl3:Ce over NaI(Tl)and CZT has also been demonstrated.

71

PTu02

Afterglow suppression and non-radiative charge-transfer in CsI:Tl,Sm R. H. Bartrama*, L. A. Kappersa, D. S. Hamiltona, A. Lempickib, C. Brecherb, V. Gaysinskiyc, E. E. Ovechkinac and V. V. Nagarkarc a

Department of Physics, University of Connecticut, Storrs, CT 06269-3046, USA b ALEM Associates, 303A Commonwealth Avenue, Boston, MA 02115, USA c Radiation Monitoring Devices (RMD) Inc., 44 Hunt St., Watertown, MA 02472, USA

CsI:Tl is a widely utilized scintillator material with many desirable properties and is the only material that approaches theoretical efficiency of scintillator response,[1] but its applicability is limited by persistent afterglow. Previous experiments have demonstrated the feasibility of ameliorating the deleterious effects of afterglow in CsI:Tl within select time domains by co-doping with Eu2+.[2],[3] In the present work, suppression of afterglow is found to be an order of magnitude more effective in CsI:Tl,Sm than in CsI:Tl,Eu. Rate equations informed by experiment predict that deep electron traps introduced by co-doping with samarium effectively scavenge electrons from shallow traps associated with thallium, thus suppressing afterglow in the time domain of tens of milliseconds. In addition, combined radioluminescence and thermoluminescence experiments on a sample of CsI:Tl,Sm with nominal concentrations of 0.11% Tl2+ and 0.2% Sm2+ suggest that ultimate recombination of electrons released by samarium with holes trapped as VKA(Tl+) centers is predominantly non-radiative in this material, thus providing a mechanism for suppression of trapped-charge accumulation in repetitive applications. A linear-coupling model in the harmonic approximation, based on ab initio quantum chemistry calculations with selective lattice relaxation, supports the conclusion that non-radiative charge-transfer transitions in CsI:Tl,Sm are enabled by the presence of low-energy 5DJ excited states of Sm2+ within the ground configuration and are mediated by spin-orbit interaction. Although these intermediate states decay primarily by a nonradiative multiphonon process, a weak magnetic-dipole radiative component facilitates monitoring of charge-transfer transitions by observation of prolonged afterglow with enhanced gain settings. We thank NIH and DOE for support of this work under Grants No. R43 RR022921-01 and DE FG02 06ER84434, respectively. * corresponding author e-mail: [email protected] References 1. Bartram R. H. and Lempicki A., “Efficiency of electron-hole pair production in scintillators”, J. Lumin. 68 (1996) 225 2. Brecher C., Lempicki A., Miller S. R., Glodo J., Ovechkina E. E., Gaysinskiy V., Nagarkar V. V., and Bartram R. H., “Suppression of afterglow in CsI:Tl by codoping with Eu2+ I. Experimental”, Nucl. Instr. And Meth. A. 558 (2006) 450 3. Bartram, R. H., Kappers, L. A., Hamilton, D. S., Lempicki, A., Brecher, C., Glodo, J., Gaysinski, V. and Ovechkina, E. E., “Suppression of afterglow in CsI:Tl by codoping with Eu2+ II. Theoretical model”, Nucl. Instr. And Meth. A. 558 (2006) 458

72

PTu03

Investigation of ZnWO4 crystals as an absorbers in the CRESST dark matter search Bavykina I.a, Angloher G.a, Proebst F.a, Petricca F.a a

Max-Planck Institute for Physics, Foehringer Ring 6, Muenchen, 80805, Germany

The goal of the CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) Dark Matter search experiment is the direct detection of Weakly Interacting Massive Particles (WIMP) via their elastic scattering off the nuclei in the target absorber. The expected WIMP event rates are supposed to be less than 0.1 event per kg and per day [1], while the background rates in well shielded detectors operated deep underground are typically orders of magnitude higher. In second phase of CRESST an active signal to background discrimination is achieved with the use of cryogenic scintillating calorimeters. The low temperature detectors employed by CRESST can discriminate between electron recoil events (caused by beta- and gamma-particles) and nuclear recoil events (caused by WIMPs and neutrons) by simultaneous measurement of phonon and scintillation light signals. A high scintillation yield in the mK temperature range is a key criterion in the choice of a scintillating absorber in the CRESST experiment. CaWO4 appears to be a satisfactory choice, providing high light yield and an excellent discrimination between electron and nuclear recoil. Nevertheless, it is beneficial to have targets with a variety of nuclei. ZnWO4 is a very interesting material in this regard. This work reports on the properties of single ZnWO4 crystals [2]. In particular, the light yield and quenching factor of ZnWO4 at mK temperature range were measured for the first time. * corresponding author e-mail: [email protected] References 1. A. Benoit, Phys. Lett. B545, (2002). 2. H. Kraus, Phys. Lett. B610, 37(2005).

73

PTu04

Charge carrier and exciton dynamics in LaX3:Ce3+ scintillators (X=Br, Cl) G. Bizarri, P. Dorenbos* Faculty of Applied Sciences, Delft University of Technology Mekelweg 15, 2629JB Delft, The Netherlands

The scintillation yield, scintillation decay time, and X-ray excited emission spectra of LaBr3 doped with 0.2%, 0.5% and 5% cerium, and LaCl3 doped with 0.5% and 10% were studied between 80 K and 600 K. The results are analyzed and interpreted with a model that comprises prompt charge carrier trapping by Ce (II) and delayed excitation of Ce by means of thermally activated transfer (IIIF), and transport (IIIS) of self trapped exciton defects.1 The results of the study provide detailed information on the scintillation mechanism. Besides presenting new experimental data, the different energy transfer processes are quantified.2

100

T = 100 K

III S II

10

Intensity (Arb. units)

1000

III F

T = 225 K

II III S

1000 100

T = 312 K

II= III F= III S

10 1 T = 400 K

1000 II= III F= III S

100 10

(a)

100

1000

Time (ns)

Figure 1: Temperature dependence of Ce scintillation time profiles in LaBr3:0.2%Ce3+ for a measurement recorded on a long time domain in a log-log scale representation. Curves labelled II , IIIF , IIIS are the fitted decay components. This work was financed by the Idaho National Engineering and Environmental Laboratory and the USA Department of Energy. We thank the company Saint Gobain, division crystals and detectors, Nemours, France for providing the scintillators used in this work. * corresponding author e-mail: [email protected] References 1. G. Bizarri, J. T. M. de Haas, P. Dorenbos, C. W. E. van Eijk, Phys. Stat. Sol. A 203, R41 (2006). 2. G. Bizarri, P. Dorenbos, submitted to Phys. Rev. B

74

PTu05

An advanced scintillator-based Compton telescope Peter F. Bloser*, James M. Ryan, Mark L. McConnell, John R. Macri University of New Hampshire, Space Science Center, 39 College Road, Durham, NH, 03824, USA

Medium-energy gamma-ray astronomy is in need of a new mission in the 0.5-20 MeV energy band to build on the success of the COMPTEL instrument on the Compton Gamma Ray Observatory. COMPTEL, which operated from 1991-2000, employed organic liquid and inorganic NaI scintillators as the detectors for imaging and measuring the energy of Compton scatter events from cosmic gamma rays [1]. A time-of-flight (ToF) measurement between the two detector types was used to reject background from atmospheric gamma rays and cosmic-ray interactions. New scintillator materials, such as LaBr3:Ce, offer a potentially straightforward and low-cost way to greatly improve on the performance of COMPTEL in a medium-scale mission. The increased stopping power and energy resolution of LaBr3 (compared to NaI) will improve the telescope’s efficiency and response, and the much faster light decay time will improve the background rejection via a narrower ToF acceptance window. We present Monte Carlo simulations of a scintillator-based Compton telescope, based on the measured properties of LaBr3, and discuss the potential for a medium-scale astrophysics mission based on this technology. * corresponding author e-mail: [email protected] References 1. V. Schönfelder, et al., Astrophysical Journal Supplement Series 86, 657 (1993).

75

PTu06

Electronic structure studies of Ce-doped gamma detector materials Andrew Canning, Rostyslav Boutchko, Stephen Derenzo, Lin-Wang Wang and Marvin J. Weber Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, U.S.A.

Cerium doped materials such as the Lanthanum Halides represent some of the brightest known scintillators for the detection of gamma rays. The scintillation process in Cerium doped materials corresponds to the transition from a 5d to 4f state on the Cerium atom where the 4f and 5d states must lie in the gap of the host materials. We have performed electronic structure calculations for many different Cerium doped materials using density functional based methods to determine the positions of the 4f and 5d states relative to the valence and conduction bands of the host materials. We find good agreement with experimental results for the systems studied in particular for the Lanthanum Halides. Our theoretical calculations will be used as a first step screening for candidate new detector materials. Supported by DHS DNDO grant HSHQDC07X00170. * corresponding author e-mail: [email protected]

76

PTu07

Luminescence and scintillation properties of barium and strontium iodides doped with rare-earth ions V. Cherginets*, B. Grinyov, N. Galunov, T. Ponomarenko, L. Trefilova, O. Tarasenko, O. Zelenskaya, V. Alekseev, N. Kosinov, A. Litichevsky Institute for Scintillation Materials, NAS of Ukraine, 60 Lenin Ave., Kharkov, 61001 Ukraine

The present work continues the investigations of luminescent and scintillation properties of Ce- and Eu-activated alkaline earth halides [1-3]. BaI2:Eu, BaI2:Ce and SrI2:Eu single crystals doped with 0.2 mol.% of the corresponding rare-earth halide were grown by Bridgman method. The radioluminescence of BaI2:Eu crystal gives the single band spectrum with the maximum at 428 nm. There is not long-wave luminescence in 520-530 nm range which accompanies for some BaI2:Eu crystals the activator luminescence [1]. The radioluminescence spectrum of a SrI2:Eu crystal consists of two bands with maxima at 430 and 525 nm. The band at 430 nm (FWHM is 0.23 eV) in the luminescence spectrum of SrI2:Eu and the band at 428 nm (FWHM is 0.25 eV) in the spectrum of BaI2:Eu crystal are caused by 5d-4f transitions in Eu2+ ion. Like the band with maximum at of 523 nm in the spectra BaI2:Ce [1] the long-wave band observed in the radioluminescence spectrum of SrI2:Eu might be caused by recombination of F-Vk pairs. The luminescence spectrum of BaI2:Ce crystal includes wide non-elementary band with the maximum at 489nm (FWHM is 0.63 eV). The absence of duplet structure in the short-wave region spectrum, that is typical for Ce3+ ions, allows the sumption that the dopant exists in the form of Ce3+-O2– charge-compensating pairs [1] in the investigated crystals. The emission generated on these centers is strongly overlapped with 525 nm emission that has non-activator nature. The data on density, the spectral composition of radioluminescence and light yield (comparatively to NaI:Tl) of the studied crystals are presented in the Table. Scintillations pulse shapes of BaI2:Eu, BaI2:Ce and SrI2:Eu are studied by delay coincidence technique. Table. Characteristics of NaI(Tl), BaI(Eu), SrI2(Eu), BaI2(Ce) crystals detector

density, g/cm3

NaI:Tl BaI2:0.2%Eu SrI2:0.2%Eu BaI2:0.2%Ce

3.67 4.92 4.55 4.92

137

Cs, 662 keV

λmax, nm 415 428 430; 525 489

Light yield, % 100 15.1 76.3 10.5

* corresponding author e-mail: [email protected] References 1. J. Selling, G. Corradi, M. Secu, S. Schweizer, Proceeding of 8th Int. Conf. on Inorganic Scintillators and Their Use in Scientific and Industrial Applications, 2006, P.415. 2. Jinho Moon, Sunghwan Kim, Wan Kim, et al., ibid, P.1291

77

PTu08

ZnSe radiation detector with various signal collecting method Y.H. Choa, S.H. Parka, W.G. Leeb, J.H. Haa, H.S. Kima, S.M. Kanga, Y.K. Kimc* , J.K. Kimc, and N. Starzhinskiyd a

Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong, Daejeon, 305-353, Republic of Korea b iTRS, HIT Building, Hanyang University, 17 Hangdang-dong, Seongbuk, Seoul, 133-791, Republic of Korea c Department of Nuclear Engineering, Hanyang University, 17 Hangdang-dong, Seongbuk, Seoul, 133-791, Republic of Korea d STC for Radiation Instruments, Institute for Single Crystals, Kharkov, 61001 Ukraine

Growing interest has been focused on the development of new radiation detector. It can include A2-B6 compound semiconductor. ZnSe has been studied extensively for application in radiation measurement1,2). The aim of the present work is to study the radiation response of ZnSe with different thickness and activator, when various signal collecting methods are used. The ZnSe crystals were delivered from the STC Institute for Single Crystals, Kharkov, Ukraine. The crystals contain activators, Te and O, and the crystal thickness are 1, 2, and 3 mm. Three methods are used to obtain the charge signal from the crystal. i) The ZnSe crystal is coupled to PIN photodiode, ii) the ZnSe crystal is coupled to photomultiplier, and iii) metal contacts are deposited on the crystal. The γ-ray energy spectra are measured with the radiation energy from 60 keV to 660 keV. The energy resolution, the peak-to-valley ratio, and the tail in the lower energy region of each spectrum are compared. These results show that ZnSe could be applied to high-resolution γ-ray measurement. 60

Counts

40

FWHM : 3.2 %

20

0

0

500

1000

1500

2000

Channel

Figure 1: 57Co energy spectrum measured with ZnSe

. This work has been carried out under the Nuclear R&D program of the Ministry of Science and Technology (MOST) of Korea. We are also supported by the SRC/ERC program of MOST/KOSEF. * corresponding author e-mail: [email protected] References 1. V. Ryzhikov et al., IEEE Trans. Nucl. Sci. 48(3), 356 (2001) 2. M. Balcerzyk et al., Nucl. Instr. Meth. A 482, 720 (2002).

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Structural and scintillation properties of cerium–doped Ba2LaF7 and Ba2LaCl7 A. Edgara, M. Bartleb, S.G. Raymondc, G.V.M Williamsc, and C. Varoya a

MacDiarmid Institute, School of Chemical and Physical Sciences, Victoria University, Kelburn Parade, Wellington, New Zealand. b Institute of Geological and Nuclear Sciences, Gracefield Road, Lower Hutt, New Zealand. c Industrial Research Limited, Gracefield Road, Lower Hutt, New Zealand.

Polycrystalline samples of Ba2LaX7 (X=F, Cl) with and without Ce doping have been prepared from the melt. The chloride material is opaque and hygroscopic, but the fluoride is transparent even in ceramic form. The compounds are found to crystallise in a cubic CaF2 lattice with the Ba and La being disordered on the cation site. The excess halide implicit in the stoichiometry representation {(Ba 2/3 La1/3)X2}X1/3 is presumed to occupy interstitial sites, and this is consistent with the measured densities. When doped with trivalent cerium, ceramic samples show photoluminescence emission peaks at room temperature at 340 nm for Ba2LaF7 and 350, 372 nm for Ba2LaCl7; the photoluminescence lifetimes are 31 and 25 ns respectively. No photopeak is apparent in these materials when irradiated from a 137Cs source, and so the scintillation light yield is difficult to measure, but estimates are made based on a comparison between the pulse height spectra from NaI (Th), the plastic scintillator NE102A and the two halides reported here. The scintillation pulses when viewed on an oscilloscope have both fast and slow components with lifetimes similar to that observed for the well-studied cases of CeF3 and Ce-doped LaF3 (see references in [1]) and we compare here the performance of the two classes of scintillator. We also report on the temperature dependence and cerium concentration dependence of the optical spectra for Ce-doped Ba2LaX7. * corresponding author e-mail [email protected] References 1. P. Lecoq et al, “ Inorganic Scintillators for Detector Systems”, Springer, Berlin, (2004)

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Vacuum deposited ZnSe(Te) scintillating layers A. Fedorov*, K. Katrunov, A. Lalayants, V. Nesterkina, N. Shiran, S. Tretyak Institute for Scintillation Materials, 60, Lenin Ave., Kharkov 61001, Ukraine Besides its known semiconductor features, properly treated ZnSe exhibits the competitive scintillation properties. Usually ZnSe(Te) scintillator is used as a bulk material, however comparely thin scintillation layers are preferable for imaging applications due to increased spatial resolution. In the present communication scintillaton properties of the vacuum condensed ZnSe(Te) layers are discussed. ZnSe layers doped with Te were prepared by physical vapor deposition. Additional treatment was applied to provide it the scintillation features. ZnSe(Te) layers possessed polycrystalline structure with domination of the (111) growth direction. Both photoluminescent and radioluminescent (under 25 kV operated X-ray tube radiation) spectra had shown the strong 640 nm band that is similar to the bulk ZnSe(Te) scintillator. Layers exhibited the considerable light output that is shown on the Figure 1 in comparison with the bulk ZnSe(Te) specimen. c

b a

Figure 1: Light signal levels obtained with the Hamamatsu photodiode from 460 mkm thick ZnSe(Te) layer on the graphite substrate (a), 380 mkm thick layer on the Al2O3 ceramic substrate (b) and bulk 1 mm thick ZnSe(Te) specimen (c), all under X-ray tube radiation at 120 kV.

Another remarkable feature of the vacuum deposited ZnSe(Te) layers is their columnar-like morphology that indicates the SZM growth mode. In conjunction with the comparely large film thickness this allows to suppose the possible spectroscopic applications of vacuum deposited ZnSe(Te) scintillation layers. * corresponding author e-mail: [email protected]

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The ZnSe(O) - perspective scintillation material for medical computer tomography V. Ryzhikova, B. Grinyova, S.Galkina*, N. Starginskia, V. Silina, S. Naidenova, P. Lecoqb a

Institute for Scintillation Materials NAS of Ukraine, Kharkov, Ukraine 60 Lenin ave., 61001, Kharkov, Ukraine b CERN, 1211 Geneva 23, Switzerland

The ZnSe(O) have a high conversion efficiency (22%) and low level of afterglow. Also due to the nonhydroscopy and high level of concordance of luminescence spectrum and sensitivity region of Si-photodiods (90 %) it also has essential preferences when compared to the other scintillators. It is especially important for the low-energy detectors production. This material gains more and more wide application in medical homographs, which have the high spatial resolution, diminish influence of radiation on a patient due to the high sensitivity of detectors and their enhanceable fast-acting. This work covers the results of scintillation parameters testing of a series of ZnSe(O) scintillators and 2D-matrices. The samples of crystals sized 1·24·38 mm3 were cut out from a crystalline ingot with 50 mm diameter. Measurements of relative light output, time decay, level of afterglow through 3 ms and homogeneity of light output of ZnSe(O) scintillators were conducted. It was determined that the light output of ZnSe(O) scintillators lies within 200 – 270 % as compared to CdWO4. The variation of light output for the crystalline boule as well as for 5 crystalline boules was limited by +/- 7 % and this is agreed with the standards. Decay time for all samples varied within the limits of 1,8 - 3 μs, and the level of afterglow through 3 ms did not exceed 0,01%. The tests of thermal and radiation stability, mechanical strength and chemical stability of this material according to humid air and acid reagents were conducted. Measurements of sctintillation parameters were carried out for 2D-matrices with pixels sized by 1.0, 1.5, and 2 mm2. The research described in this publication was made possible in part by INTAS (Project # 05-104-7519) and STCU (Project # 4115). * corresponding author e-mail: [email protected]

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Luminescence properties and morphology of ZnSe(Te) films V.Gaysinskiy*, V.Nagarkar, B.Singh, L.Ovechkina, S.Miller, S. Thacker Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA 02472, USA

High-speed imaging applications, such as time resolved X-ray diffraction, require detectors with high frame rates ranging from hundreds to thousands of frames per second. New high resolution CCD imagers capable of operating at the required frame rates have been developed, however, the current X-ray to light converters are the performance limiting factor in such applications. Here we report on the development of a structured ZnSe:Te scintillator that promises to provide extraordinarily high scintillation efficiency, emission at 610 nm (which is ideally suited for CCD sensors), high density of 5.4 g/cm3, and a fast decay time of ~3 μs with no afterglow, which permits high speed imaging without the problem of ghosting due to persistence. Furthermore, the non-hygroscopic and non-toxic nature of the ZnSe(Te) scintillator, along with its stability of response over a wide range of temperatures and extremely high levels of radiation, makes it an ideal material for radiation detection in general and for synchrotron applications in particular[1]. While ZnSe as an infrared window material is established, introduction of an isovalent Te impurity in ZnSe crystals to control its luminescence properties is relatively new[2]. Significant work on the crystal growth of ZnSe, and some work on fabricating powdered ZnSe screens[3] has since been reported, but no attempts have been made to fabricate it in a columnar form needed for high-resolution imaging. At RMD, we have fabricated microcolumnar ZnSe:Te films measuring ~30 μm to 85 μm in thickness using co-evaporation of ZnSe and ZnTe on suitable substrates. These films show excellent structure with columns ranging from 0.2 μm to 5 μm in diameter. The scintillation light produced by the radiation interaction is channeled within the microcolumns by the mechanism of total internal reflection, thereby providing very high spatial resolution. Performance of these films in terms of their light output, spatial resolution, spectral distribution, decay time, and afterglow will be presented. We thank US Department of Energy (DOE) for support of this work under Grant No.DE-FG02-06ER84402. * Corresponding author e-mail: [email protected] References 1. V. V. Nagarkar, B. Singh, V. Gaysinskiy, S. Miller, S. Thacker, L. Guo, D. Gore, and T. C. Irving, “EMCCD-based detector for time-resolved X-ray diffraction and scattering studies of biological specimens,” Accepted for publication, IEEE Trans. Nucl. Sc. (2007). 2. V. Ryzhikov, G. Tamulaitis, N. Starzhinskiy, L. Gal’chinetskii, A. Novickovas, J. Lumin., 101 (2003) 45. 3. Bruker AXS Inc., Advanced X-ray Solutions, http://www.bruker-axs.com

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Measurement and simulation of the neutron response and detection efficiency of a Pb-scintillating fiber calorimeter M. Anelli a, G. Battistoni b, S. Bertolucci a, C. Bini c, P. Branchinid, C. Curceanua, G. De Zorzi c, A. Di Domenico c, B. Di Micco d, A. Ferrari e, P. Gauzzi c, S. Giovannella a, F. Happacher a,*, M. Iliescu a,f , M. Martini a, S. Miscetti a, F. Nguyen d, A. Passeri d, A.Prokofiev g, P.Salab, B. Sciascia a, F. Sirghi a,f a Laboratori Nazionali di Frascati, INFN, Italy b Sezione INFN di Milano, Italy c Universit`a degli di Studi “La Sapienza” e Sezione INFN di Roma, Italy d Universit`a degli di Studi “Roma Tre” e Sezione INFN di Roma3, Italy e Fondazione CNAO, Milano, Italy f IFIN-HH, Bucharest, Romania g The Svedberg Laboratory, Uppsala University, Sweden The overall detection efficiency to neutrons of a small prototype of the KLOE Pb scintillating fiber calorimeter has been measured at the neutron beam facility of The Svedberg Laboratory, TSL, Uppsala, in the kinetic energy range [5,175] MeV. The measurement of the neutron detection efficiency of a NE110 scintillator provided a reference calibration. At the lowest trigger threshold, the overall calorimeter efficiency ranges from 40 % to 50 %. This value largely exceeds the estimated 8−16 % expected if the response were proportional only to the scintillator equivalent thickness. A detailed simulation of the calorimeter and of the TSL beamline has been performed with the FLUKA Monte Carlo code. The simulated response of the detector to neutrons is presented, as well as a first data-Monte Carlo comparison. The results show an overall neutron efficiency of about 50 %, when no trigger threshold is applied. The reasons of such an efficiency enhancement, in comparison with the typical scintillator-based neutron counters, are explained, opening the road to a novel neutron detector. * Corresponding author Fabio Happacher e-mail address: [email protected] References 1. Anna Ferrari, Measurement and simulation of the neutron response and detection efficiency of a Pbscintillating fiber calorimeter Preprint submitted to the XIth VCI 2007

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Scintillation properties of a BaxSr1-xCl2 single crystal Jungin Kima, Heedong Kanga*, H.J. Kima, H. Parka, Sunghwan Kimb, Sih-Hong Dohc a

Kyungpook Nat’l University, Daegu, 702-701, KOREA b Daegu Health College, Daegu, 702-722, KOREA c Pukyung Nat’l University, Busan, 608-737, KOREA

The development of a new scintillator has become a very active one during the last two decades [1]. In this paper, the new single crystals of BaxSr1-xCl2 were studied over ranges of x and were grown Ba0.12Sr0.88Cl2, Ba0.2Sr0.8Cl2 and Ba0.22Sr0.78Cl2 by using the Czochralski technique. The crystals were cut into a size of 10×10×5 mm3 dimension. The emission and excitation spectra of the crystals were measured with UV excitation. Scintillation properties of the crystals such as pulse height spectra, energy resolution, α/β ratio, relative light-output, proportionality curve, and fluorescence decay time were measured with the radioactive gamma ray source at room temperature. The light output of these crystals were compared with that of the CsI(Tl) crystal. The differences of relative light output, energy resolution, and decay time among these crystals were studied in detail. This work was supported by the SRC/ERC program of MOST/KOSEF (R11-2000-06702001-1). * corresponding author e-mail: [email protected] References 1. Mikhail Korzhik, Poul Lecoq, IEEE Trans. Nucl. Sci., 48, 628 (2001).

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Intrinsic luminescence of single crystalline films and single crystals of LuAP and LuAP:Ce perovskites Yu. Zorenkoa, V. Gorbenkoa, T. Voznyaka, T. Zorenkoa, V. Mikhailinb, V. Kolobanovb, N. Petrovninb, D. Spasskyb a

LOM, Department of Electronics, Ivan Franko National University of Lviv, 79017 Lviv, Ukraine b Physical Faculty, Moscow State University, 119899 Moscow, Russia

Single crystal (SC) of LuAlO3:Ce perovskite (LuAP:Ce) with large effective atomic number (Zef=65) is well-known scintillators for medical application [1]. The technology of liquid phase epitaxy (LPE) offers also the possibility of obtaining the perfect highdensity single crystalline film (SCF) scintillators [2]. In comparison with the SC, the SCF of perovskites, grown from the melt-solution at low (950-1050°C) temperatures in air, are characterized by absence of antisite defects (AD) and extremely low concentrations vacancy-type defects (VD) [3]. Therefore, SCF are now convenient model objects for studying the intrinsic luminescence, especially exciton-related luminescence, in complex oxides [4]. For instance, position of exciton peak, energy gap and their temperature dependences were determined exactly for first time in LuAP SCF [5]. The intrinsic luminescence LuAP and LuAP:Ce SCF, growth by LPE on YAP substrates from melt-solution (MS) based on PbO-B2O3 flux and row materials of 5N purity in comparison with SC analogues was investigated under excitation by synchrotron radiation at BW3 and Superlumi experimental station with an energy of 70-900 eV and 3.7-40 eV, respectively. Main attention was given to the determination of the fundamental parameters related to the host and Ce3+ luminescence in LuAP. The position of self-trapped exciton (STE) emission bands peaked at 6.13 eV (9 K) and 5.95 eV (at 300 K) and their complex decay kinetics were determined at 9 K range for LuAP and LuAP:Ce SCF. The fine structure of excitation band shows that the relaxed excited states (RES) of STE emission have at least two radiative levels. The second lowintensity band of intrinsic emission of LuAP and LuAP:Ce SCF peaked at 280 nm probably is related to the localized exciton (LE) emission around impurity/defect centers [3, 4]. In SCF, such centers can be formed mainly by Pb2+ trace impurity coming from the flux during SCF growth [4]. The intensity and position of intrinsic emission bands in LuAP and LuAP:Ce SC are notably modified with respect to SCF due to AD and VD presence and existence of the LE (AD) and LE (VD) emission band peaked at 5.50 and 4.42 eV, respectively. The role of AD and VD in LuAP:Ce SC in delaying the energy transfer to Ce3+ ions during the transport stage is discussed. The work was supported by INTAS grant 04-78 -7083. corresponding author e-mail: [email protected] References 1. Lempicki, et al. Proc. SCINT 95’ p.340 (1995). 2. Yu. Zorenko, V. Gorbenko, I.Konstankevych, M.Pashkovsky, B.Grinyov, et al. Proc. SCINT99’, 476 (1999) 3. Yu. Zorenko, V. Gorbenko, I.Konstankevych, et al., Radiat. Meas. doi:10.1016/j.radmeas.2007.0.046 (2007) 4. Yu. Zorenko, A. Voloshinovskii, V. Gorbenko, T. Zorenko, M. Nikl, K. Nejezchleb, pss (c) 4, 963 (2007). 5. V. Kolobanov, V. Mikhailin, N. Petrovnin, D. Spassky, Yu. Zorenko, pss (b) 243, R60-R62 (2006).

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Ce-doped YAG and LuAG epitaxial films for scintillation detectors M.Kuceraa*, K. Nitschb, M. Kubovaa, N.Solovievab, M.Niklb, J.A.Maresb a

Charles University, Faculty of Mathematics and Physics, Ke Karlovu 5, 12116 Prague, Czech Republic b Institute of Physics AS CR, Cukrovarnická 10, 16253 Prague, Czech Republic

Thin epitaxial films represent an interesting alternative to bulk single crystals for 2D imaging scintillation screens. We have studied the growth and properties of Ce3+- doped Y3Al5O12 (Ce:YAG) and Lu3Al5O12 (Ce:LuAG) garnet thin films prepared by the isothermal dipping liquid phase epitaxy (LPE). Such single crystalline films can be produced in required thickness and at relatively low temperatures (~1000 °C) compared to their bulk counterparts grown by the Czochralski method (~1900 °C). The aim of this work is to study the effect of flux composition and growth conditions on the crystallographic, optical, and emission properties of epitaxial garnet films. Different fluxes were used: the films were grown from a) PbO-B2O3, b) BaO-B2O3, and c) MoO3Li2MoO4 fluxes on YAG or LuAG substrates of (111) crystallographic orientation. The growth temperatures were from 930 to 1045 °C and corresponding thickness of films 1 – 25 μm. The films were characterized by the X-ray crystallography, optical absorption, luminescence, and by scintillation response using the alpha particles. A characteristic broad green emission round 540 nm was observed in all Ce-doped garnet films. The epitaxial films prepared from the PbO flux exhibited excellent crystallographic properties with good lattice match of film and substrate and high quality surface. However, Pb2+ and Pt4+ ions were detected in these films (Pt comes from the crucible, which reacts with the solvent). As a consequence, an increased absorption was observed in the ultraviolet range below 260 nm. Besides, a two exponential decay indicates partial quenching of luminescence coming from impurities. Films with superior luminescent properties were obtained from the BaO flux. Any trace impurities were detected neither in optical absorption nor in emission experiments and we did not observe any quenching of luminescence due to the impurities. Measurements of luminescence kinetics show on single exponential decay with a time constant of 60 ns. The emission properties of films obtained from the BaO flux are comparable with the best Czochralski grown single crystals. However, the surface morphology was inferior compared to the films obtained from other fluxes due to the higher viscosity of BaO flux. The Mo-based flux has essentially zero volatility, low reactivity with the Pt crucible, low viscosity and this flux provides films, which do not contain any solvent-related impurities. In conclusion, well-defined single crystalline garnet films were obtained using the LPE technology. Much lower growth temperatures compared to Czochralski grown crystals result in lower structural disorder and lower concentration of defects in epitaxial films. Acknowledgments: The work was supported by the grant GACR 202/05/2471. * corresponding author e-mail: [email protected]

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Performance of an 8x8 array of LaBr3(Ce) pixels coupled to a multianode PMT Shunsuke Kurosawa, Kaori Hattori, Shigeto Kabuki, Hidetoshi Kubo, Kentaro Miuchi, Hironobu Nishimura, Yoko Okada, Atsushi Takada, Toru Tanimori, Kazuki Ueno Department of Physics, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan

A LaBr3(Ce) scintillator has high light output (~60,000 photons/MeV) and fast principle decay constant (30 ns)[1]. In addition, its high energy resolution is attractive for gammaray detectors. A crystal with a diameter of 13 mm and a length of 13 mm (Saint-Gobain K. K.), for example, reached the resolution of 3.1±0.1 % (FWHM) at 662 keV with a photomultiplier tube (PMT). LaBr3(Ce) crystal, however, needs a hermetic package due to the hygroscopic property. Since a position-sensitive pixel array with high energy resolution is useful in various fields such as astronomy and nuclear medicine (ex. our works [2]). We assembled pixel arrays of several crystals such as CsI(Tl) [3] and GSO(Ce) [4] by our own technique, and have developed a LaBr3(Ce) array that consists of 8x8 pixels with each size of 6x6x13 mm3 size (Fig. 1), coupled to a 64ch multi-anode PMT (Hamamatsu K. K., H8500) with the same pitch as the crystal pixel. Figure 2 shows an energy spectrum of a 133Ba source. The energy resolutions (FWHM) were 6.4±0.1 % at 356 keV and 5.0±0.1 % at 662 keV when collimated gamma rays from the sources were irradiated to one pixel in the array. We thank Dr.Yanagida and Mr. Kadono for support in assembling the LaBr3 array.

Figure 2: The energy spectrum of 133Ba comparing with GSO(Ce) and NaI(Tl). The solid line: LaBr3 pixel, the broken line: GSO(Ce) with 25x25x13mm3 and the doted line: NaI(Tl) with a diameter of 13 mm and a height of 13 mm. * corresponding author e-mail: [email protected] Figure 1: Photograph of LaBr3 array. 6x6x13 mm3 pixels are arranged in an 8x8 array, surrounded with aluminum.

References 1. E. V. D. van Loef et al., Appl. Phys. Lett. 79, 1573 (2001) 2. T. Tanimori et al., New Astron. Rev. 48, 263 (2004) 3. H. Sekiya, K. Hattori et al., Nucl. Instr. and Meth. A. 563, 49 (2006) 4. H. Nishimura et al., Nucl. Instr. and Meth. A, in press , astro-ph/0609214

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A method of sensitivity enhancement of liquid xenon emission detectors for dark matter search Alexander Bolozdynya*, Adam Bradley, Pavel Brusov, Eric Dahl, John Kwong, Thomas Shutt Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-2069, U.S.A.

Recent measurements strongly support the hypothesis that the vast majority of mass in the universe is in the form of dark matter. One of the leading ideas is that it is composed of weakly interacting massive particles (WIMPs) created in the big bang. The WIMP hypothesis is testable with a detector of sufficient mass and sensitivity. For this purpose, several experiments (XENON, XMASS, ZEPLIN, LUX) consider massive (25 kg as of today and up to 1 ton in the near future) liquid xenon emission detectors [1]. Performance of the emission detectors directly depends on effective collection of photons (175±10 nm original spectrum) and electrons from the bulk LXe of up to 1m linear sizes [2]. The authors have considered a possibility to enhance the performance of emission detectors with wavelength shifting that allowed us to shift the spectrum of scintillation and electroluminescence light to 300-400nm. In this paper, we report on the first results of operation of our prototype (200g LXe) emission detector with p-terphenyl used as the wavelength shifter vacuum-deposited on optical surfaces.

Figure 1: Correlation of the electron life-time with temperature variations of liquid xenon

In our study, we found that p-terphenyl (pTP) allows enhancing light-collection efficiency by up to 30-40% but it is dissolving in liquid xenon that leads to a reduction in the lifetime of drifting electrons correlated with temperature of the liquid as shown in Fig.1. The results of our study and possible ways to solve the problem are discussed in the paper. * corresponding author e-mail: [email protected] References 1. T. Shutt, C.E. Dahl, J. Kwong, A. Bolozdynya, P. Brusov, “Performance and fundamental processes at low energy in a two-phase liquid xenon dark matter detector”, Nucl. Instr. Meth. A to be published in 2007 2. A. Bolozdynya, Nucl. Instr. Meth. A 422, 314-320 (1999).

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Growth and scintillation properties of ZnSe:Te and ZnSe:Al,O,Te semiconductors W. G. Leea, Y. K. Kimb*, J. K. Kimb, N. Starzhinskiyc, V. Ryzhikovc, B. Grinyovc a

Innovative Technology Center for Radiation Safety, Hanyang University, Seoul 133-791, Korea b Department of Nuclear Engineering, Hanyang University, Seoul 133-791, Korea c Institute for Scintillation Material of Science-Technology Concern “Institute for Single Crystals” National Academy of Science of Ukraine, 60 Lenin Ave., Kharkov 61006, Ukraine

Zinc selenide (ZnSe:Te and ZnSe:Al,O,Te) single crystals were grown by Bridgman– Stockbarger technique and annealed under excess Zn conditions at 1290K. The lattice constants of ZnSe:Te and ZnSe:Al,O,Te single crystals were obtained from X-ray diffractometer (XRD) data. It is found that the lattice constants of ZnSe:Te and ZnSe:O scintillators were 5.658 and 5.651, respectively. From the absorption spectra, the band gap energies of ZnSe single crystals were calculated by a linear fitting process. Under excess Zn conditions the band gap energy of ZnSe:Te single crystals increases from 2.56 eV to 2.58 eV and that of ZnSe:Al,O,Te single crystals increases from 2.44 eV to 2.46 eV. The maximum emission wavelengths of the radioluminescence of ZnSe:Te and ZnSe:Al,O,Te scintillators excited by X-rays were 630nm and 606 nm, respectively. The afterglow levels of ZnSe:Te and ZnSe:Al,O,Te scintillators after 10 ms were 0.021% and 0.010%, respectively. The energy resolutions of ZnSe:Te and ZnSe:Al,O,Te scintillators in a size of 10x10x1 mm3 were 13.7% and 13.9 %, when it was exposed to 137Cs γ-ray. This work has been supported financially by the Science Research Center (SRC) / Engineering Research Center (ERC) program of MOST/KOSEF (Korea Science and Engineering Foundation, grant # R11-2000-067-01001-0) * corresponding author e-mail: [email protected]

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Luminescence properties of ZnSe:Te and ZnSe:O crystals grown by Bridgman-Stockbarger method W. G. Leea, Y. K. Kimb*, J. K. Kimb, N. Starzhinskiyc, V. Ryzhikovc, B. Grinyovc a

Innovative Technology Center for Radiation Safety, Hanyang University, Seoul 133-791, Korea b Department of Nuclear Engineering, Hanyang University, Seoul 133-791, Korea c Institute for Scintillation Material of Science-Technology Concern “Institute for Single Crystals” National Academy of Science of Ukraine, 60 Lenin Ave., Kharkov 61006, Ukraine

Zinc selenide crystals doped with tellurium or oxygen, ZnSe:Te and ZnSe:O, were grown by Bridgman–Stockbarger technique and annealed under excess Zn conditions at 1290K for 24 hours. Luminescence properties of ZnSe:Te and ZnSe:O semiconductor scintillators were studied. The emission specrum of ZnSe:Te crystal was observed in the range of 530 nm ~ 750 nm with a peak at 630 nm and that of ZnSe:O crystal was observed in the range of 510 nm ~ 750 nm with a peak at 595 nm. The maximum emission wavelengths of the radioluminescence of ZnSe:Te and ZnSe:O scintillators excited by X-rays were 630nm and 595 nm, respectively. Photoluminescence of ZnSe crystals doped with tellurium or oxygen was measured in a temperature range of 15 k ~ 295 K. The transmittance coefficients of ZnSe:Te and the ZnSe:O crystals were 67% and 57% at their maximum emission wavelengths. The relative light outputs of ZnSe:Te and ZnSe:O were 1.55 and 1.28 times higher than for CsI:Tl. The decay curve of ZnSe:Te scintillator has three components, their values being 15 μs, 58 μs, and 122 μs, that of ZnSe:O scintillator has two components, their values being 4 μs and 14 μs. The energy resolutions of ZnSe:Te and ZnSe:O scintillators in a size of 10x10x1 mm3 were 13.7% and 7.4 %, when it was exposed to 137Cs γ-ray. This work has been supported financially by the Science Research Center (SRC) / Engineering Research Center (ERC) program of MOST/KOSEF (Korea Science and Engineering Foundation, grant # R11-2000-067-01001-0) * corresponding author e-mail: [email protected]

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Monte Carlo modeling and analysis of structured CsI scintillatorcoupled pixel detectors Chang Hwy Lima, Ho Kyung Kima*, Hyosung Chob a

School of Mechanical Engineering, Pusan National University, Busan 609-735, Republic of Korea b Department of Radiological Science, Yonsei University, Wonju 220-710, Republic of Korea

We theoretically investigate the imaging properties of columnar cesium iodide (CsI) scintillator-coupled pixel detectors by using Monte Carlo methods. For the Monte Carlo geometry, we have modeled an imaging pixel detector into simple three-layer geometry: columnar CsI, silicon dioxide (SiO2) and silicon substrate. For the realistic optical coupling behavior, the silicon dioxide and silicon layers were included in the model. The columnar CsI layer was simplified to a cylinder array, regularly formatted in 10-μm pitch, covering 10 × 10 mm2. The cylinder diameter is 8 μm. In the simulation, the main tally is the collected optical photon spatial distribution at the detection plane, resulting in a presampled point-spread function (PSF). In order to imitate the spatial sampling process by the pixellated photodiode array, we performed aperture integration for the distribution considering pixel fill factor. Figure 1 shows an illustrative example of the simulation concerning the light collection efficiency as a function of the aspect ratio of a CsI column. We also considered Lubberts effect[1], which is that the normalized frequency-dependent correlated noise transfer function of an homogenous scintillator is not proportional to the normalized MTF (modulation-transfer function) at the output of the screen. To do this, the depth-dependent energy absorption was simulated for the incident x rays. As Monte Carlo codes, we used MCNPXTM (Version 2.5.0., ORNL, USA) and DETECT2000 (Laval University, Quebec, Canada) for x rays and optical photons transport, respectively. These Monte Carlo models and analysis will be useful for the better design of digital xray imaging detectors.

Figure 1: Light collection efficiency as a function of the aspect ratio of a CsI column.

This work was supported by Grant No. R01-2006-000-10233-0 from the Basic Research Program of the Korea Science & Engineering Foundation. * corresponding author e-mail: [email protected] References 1. G. Lubberts, J. Opt. Soc. Am. 58, 1475 (1968).

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”Semi-transparent” X-ray beam monitor based on nanometric phosphor powder deposited on thin carbon plate T. Martina*, P.P. Jobertb, F. Lesimplea, G. Baretb a

ESRF, 6 rue Jules Horowitz, Grenoble, 38043, France DGTec SAS, 178 rue de Mayoussard, Centr’Alp,Moirans, 38430, France

b

Synchrotron sources provide increasingly smaller X-ray beams (sub-micrometric size) and experiments are, of course, more sensitive to X-ray beam movement owing to thermal effect or machine vibration. Sensors used to evaluate in-situ the position and shape of the beam are a powerful diagnostic device to compensate the variation of the beam by feedback correction [1,2]. Powder of nanometric size, 100nm diameter, of europium-doped gadolinium oxide has been prepared and deposited by spin-coating on quartz substrate for evaluation and finally on a thin vitreous carbon plate for “semitransparent” X-ray beam monitor applications and detector alignment purposes. The 400nm thick layer allows to measure the beam position with only 8% X-ray absorption at 14keV. 92% of the X-ray beam is still available to investigate a diffraction pattern or a tomography of a sample [3]. Powder size, annealing temperature, rotation speed and thickness of the layers are key parameters to optimize the optical quality and light yield of the thin phosphor screen. A low-cost 2D detector has been set up at the European Synchrotron Radiation Facility (ESRF). The system, based on lens coupling and a digital CCD camera allows a sub-micrometer precision measurement as well as beam profile information. * corresponding author e-mail: [email protected] References 1. R.W. Alkire et al. , J. Synchrotron Rad. 7, 61-68 (2000). 2. P. Fajardo and S. Ferrer, Rev. Sci. Instrum. 66(2), 1879 (1995). 3. C. Dujardin et al., NIM A 537, 237-241 (2005) .

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CASTER – A LaBr3-based gamma ray imager for NASA’s Black Hole Finder Probe Mark L. McConnella*, Peter F. Blosera, Gary L. Caseb,c, Michael L. Cherryb, James Cravensd, T. Greg Guzikb, Kevin Hurleye, R. Marc Kippenf, John R. Macria, Richard S. Millerg, William Paciesasg, James M. Ryana, Bradley Schaeferb, J. Greg Stacyb,c, W. Thomas Vestrandf, and John P. Wefelb, a

University of New Hampshire, Space Science Center, Morse Hall, Durham, NH 03824 Louisiana State University, Department of Physics and Astronomy, Baton Rouge, LA 70803 c Southern University, Department of Physics, Baton Rouge, LA 70813 d Southwest Research Institute, Department of Space Science, San Antonio, TX 78228 e Space Sciences Laboratory, University of California, Berkeley, CA 94720 f Los Alamos National Laboratory, Los Alamos, NM 87545 g University of Alabama, Department of Physics, Huntsville, AL 35899

b

The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X-ray coded-aperture imaging mission operating in the 10-600 keV energy band, a spectral range that is considered to be especially useful in the detection of black hole sources. The development of new inorganic scintillator materials provides improved performance (for example, with regards to energy resolution and timing) that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator-based gamma cameras. Here, we discuss the Coded Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that represents a BHFP based on the use of the latest scintillator technology. The baseline concept envisions an array of coded aperture imagers with a total detection area of 6-8 m2. The detection planes consist of arrays of LaBr3 modules that provide event location accuracies of 1-2 mm and energy resolution of ~ 3% at 662 keV. * corresponding author e-mail: [email protected]

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Using thin films to rapidly screen potential scintillators B.D. Milbrath*, J.A. Caggiano, D.W. Matson, L.C. Olsen Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99354, USA

Growing crystals of inorganic scintillators is a time-consuming and expensive process, slowing the discovery of new radiation detection materials. One can use polycrystalline thin films and powders to perform some characterization measurements of a material’s scintillation ability before proceeding to crystal growth. Introduction of grain boundaries, however, introduces traps and optical scattering. Optical scattering is especially problematic for powders, where the light produced at a depth much greater than crystal size is almost entirely lost. Thin films should provide a better indication of a material’s potential than powders due to their increased optical transmission. To that end, we have begun an investigative program to discern the usefulness of this technique for scintillator characterization. As a first step, we made 10 micron thick films of Eu-doped CaF2 by electron beam deposition, which took approximately 1.5 hours per sample. After confirming composition with XPS and crystal structure with GIXRD, photoluminescence measurements were performed and found to be in agreement with literature values. Photopeak comparisons can be performed using alpha sources. The method provides a quick way to explore and optimize the proper dopant amount. The crystal structure of the thin films results in grain sizes of approximately 15 nm. Light yields were approximately 10% those found in commercial, single-crystal materials. Subsequent to the CaF2 studies, we have begun to make thin Ce halide films. Rare-earth halide scintillators are an area of much current activity due to the favorable energy resolutions and light yields some of them possess. The Ce halide series allows us to explore the manufacture of thin films of this type, including their hygroscopicity. Use of thin films to rapidly study combinatorial materials from this series will also be investigated. Preliminary results from our Ce halide studies will be presented along with our CaF2(Eu) results.

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EPR, F+ centers, and afterglow in bulk and nanophosphor oxyorthosilicates D. W. Cookea*, M. W. Blairb, J. F. Smitha, M. K. Bacraniac, B. L. Bennetta, L. G. Jacobsohna, E. A. McKigneyc, and R. E. Muenchausena a

Materials Science & Technology, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Earth & Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545 USA c Safeguards Science & Technology, Los Alamos National Laboratory, Los Alamos, NM 87545, USA b

Lu2SiO5:Ce (LSO) and Y2SiO5:Ce (YSO) oxyorthosilicate nanophosphors have been synthesized and examined by electron paramagnetic resonance (EPR) spectroscopy and luminescence techniques, and the results have been compared with their bulk counterparts. Nanophosphors exhibit red-shifted emission, increased Stokes shift, and enhanced oscillator strength. [1] EPR spectra of nano-YSO obtained at 10 K exhibit Ce3+ resonances with g values of 2.652 and 1.555 compared to bulk values of 2.348 and 1.610. In addition to shifts in the g values, there is considerable line broadening of the nanophosphor resonance. Yttrium-oxygen atomic disorder and concomitant perturbation of the local crystalline electric field account for these observations. Note that Ce substitutes for the rare-earth ion of the host lattice in bulk and nanophosphor oxyorthosilicates. Similar results are obtained for nanophosphor LSO, although the resonances are shifted because of the larger Lu-O arrangements. An additional narrow resonance (ΔHpp = 15 G) with g = 2.005 is observed in bulk and nanophosphor LSO and YSO, which is attributed to the F+ center, i.e., an electron trapped at an oxygen vacancy of the host lattice. This center is correlated with a thermally stimulated luminescence peak that occurs nears 375 K in bulk and nanophosphor LSO and YSO. The thermal activation energy of this trapped electron is ~ 1 eV, which is nearly coincident with the first excited state of the Ce3+ electronic manifold. We propose a model of energy transfer between these states that adequately explains the observed complex afterglow in oxyorthosilicates. Research supported by the DOE Office of Basic Energy Sciences * corresponding author e-mail: [email protected] References 1. D. W. Cooke et al., Appl. Phys. Lett. 88, 103108 (2006).

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Application of 6LiI(Eu) scintillators with photodiode readout for neutron counting in mixed gamma-neutron fields Guntram Pauscha*and Juergen Steina,b a

ICx Radiation GmbH, Koelner Str. 99, D-42651 Solingen, Germany ICx Radiation Inc., 100 Midland Road, Oak Ridge, TN 37830, Tennessee

b

Neutrons from spontaneous or induced fission indicate the presence of Special Nuclear Material (SNM). That is why ANSI and IAEA standards require hand-held Radio-Nuclide Identification Devices (RID) to be equipped with neutron detectors. Due to space limitations the detection performance must be achieved at minimum detector size. For obtaining efficiency in a small volume instrument, a high gas pressure for He-3 tubes is essential. However, pressurized devices above 2.8 atmospheres are conflicting with international transport regulations. As an alternative, scintillators containing 6Li or other constituents with large neutron capture cross section combine small size with superior efficiency while preventing the safety risks due to high gas pressure. 6LiI(Eu) scintillators with photomultiplier readout can even be deployed as combined neutron and gamma detectors. The light yield of neutron capture signals corresponds to 3-4 MeV gamma equivalent energy, providing for discrimination against gammas from radioactive decays. The energy resolution of ~7.5% measured for 662 keV gamma radiation [1,2] is poor compared to the ~3% achieved with LaBr3(Ce) detectors [3]. The present paper focuses on neutron counting with 6LiI(Eu) using digital electronics. The combining of this scintillator with a large-area photodiode (PD) results in a compact, efficient design [4]. Digitized signals of a 6LiI(Eu)-PD combination were processed with standard algorithms. An energy resolution of 6.5% measured for the neutron capture peak in spite of the PD noise contribution and a basic detector configuration was sufficient for discrimination against gamma counts in the scintillator. Signals due to direct x-ray or gamma interactions with the PD bulk material turned out to be a serious source for interference. Such events are unavoidable in mixed gamma-neutron fields and generate pulse amplitudes interfering with the spectrum of neutron capture signals. Since scintillation signals can be identified by the increased rise time caused by the light decay in 6LiI(Eu), pulse shape analysis provides a means for suppressing these bulk events. Measurements demonstrate excellent separation of neutron captures from x-ray and gamma background by applying algorithms to signals at sampling rates of 10 MS/s. Such systems can be realized with state of the art miniaturized electronics. * corresponding author e-mail: [email protected] References 1. M. Swoboda, R. Arlt, et al., IEEE Transact. Nucl. Sci. 52, 3111 (2005). 2. A. Syntfeld, M. Moszyński, et al., IEEE Transact. Nucl. Sci. 52, 3151 (2005). 3. G. Bizarri, J.T.M de Haas, P. Dorenbos, C.W.E. van Eijk, IEEE Transact. Nucl. Sci. 53, 615 (2006). 4. V.D. Ryzhikov, E.A. Danshin, et al., 1997 IEEE Nucl. Sci. Symp., Conference Record, 767 (1997).

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Combinatorial thin film synthesis of scintillation materials J.D. Peaka,b*, C.L. Melchera,b, P.D. Racka,b a

Materials Science and Engineering, University of Tennessee, Knoxville, 37996-2200, U.S.A. Scintillation Materials Research Center, University of Tennessee, Knoxville, 37996-2000, U.S.A.

b

Large scintillator crystals are often grown via time consuming processes such as the Czochralski and Bridgman techniques. The search for faster and more efficient scintillator crystals can be limited by the time consuming nature of the crystal growth. In this work, we will illustrate the use of a combinatorial thin film synthesis process that is being used to explore new scintillator materials. The combinatorial synthesis process utilizes three individual rf magnetron sputtering sources which can be simultaneously powered to generate a wide composition space of binary or ternary systems. In this work, we have investigated cerium doped lutetium oxyorthosilicate (LSO) as it is currently the most widely used scintillator crystal in PET imaging and provides a good benchmark for our proposed approach. LSO thin films with a gradient of cerium doping have been deposited to investigate the effects of cerium concentration and to compare the thin film properties to those of bulk LSO crystals. We have found that the emission spectra of the thin film materials have similar characteristics compared to the bulk crystals and the integrated intensity increases with cerium concentration over the measured range. Lutetium-silicon oxide gradients and cerium doped lutetium-silicon oxide gradients have also been grown. The measured x-ray diffraction results have been correlated to the equilibrium phase diagram, and the integrated intensity of the emission spectra have been correlated with the corresponding phases of the lutetium-silicon system. In this presentation, we will discuss the combinatorial thin film synthesis process, and will correlate the observed structural, morphological, and chemical properties of the thin films to the measured optical properties. The authors would like to acknowledge Siemens Medical Imaging, Jung-Won Park, Merry Spurrier, and Piotr Szupryczynski.

Substrate

Si Lu Ce Figure 1: Photograph of the sputtering chamber during the Lu-Si oxide combinatorial synthesis * corresponding author e-mail: [email protected]

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Charge transfer luminescence of Yb-doped oxide crystals: overview, new results and perspectives C.Pedrini*a, I.Kamenskikhb, A.Petrosyanc, C.Dujardina, G.Ledouxa, N.Guerassimovab, D.Krasikovb a

Université de Lyon, Lyon, F-69003, France ; université Lyon 1, Villeurbanne, F-69622, France ; CNRS, UMR5620, Laboratoire de Physico-Chimie des Matériaux Luminescents, Villeurbanne, F-69622, France. b Physics Department, M.V.Lomonosov Moscow State University, Moscow 119992, Russia c Laboratory of Crystal Growth of Luminescent Materials, Institute for Physical Research, 378410 Ashtarak-2, Armenia

Electron transfer transitions between oxygen ligands and central ytterbium ions can be often observed in ytterbium-containing oxide crystals provided that their gap is large enough to allow localized charge transfer states. It is due to the fact that the optical electronegativity of Yb3+ is large enough, leading the first Laporte-allowed electron transfer band to arise in the UV region[1]. Absorption bands occur usually around 200230 nm and charge transfer luminescence (CTL) may be detected. CTL exhibits attractive properties for scintillator applications, in particular a fast fluorescence decay with a typical time constant of few tens of nanoseconds. But the luminescence is strongly temperature dependent with a thermal quenching occurring often below room temperature, and the light yield needs to be improved to envisage possible scintillator applications. After the early work of Nakazawa[2,3] and the investigation of a large variety of host lattices by van Pieterson et al [4], more detailed studies of various systems were undertaken to understand the radiative charge transfer recombination and to correlate the optical and scintillation properties to the crystal quality, composition and structure. The purpose of this paper is to make a survey of our many results obtained these last years essentially in garnets, perovskites and sesquioxides, to present new results on new systems, and to discuss on new perspectives of research. Acknowledgements: This work was supported by French CEA Saclay (DAPNIA), IHPContract HPRI-CT-1999-00040/2001-00140 of the European Commission, grants DFG No 436 RUS 113/437, NATO PST.CLG.9977974, YSF 00-35 (N.G.), NSh 1771.2003, RFBR 03-02-27128(IK), and presently by INTAS Ref. Nr 05-1000008-8087. It was performed under the auspices of the Crystal Clear Collaboration. * corresponding author e-mail: [email protected] References 1. C. K. Jorgensen, Progr. Inorg. Chem. 12, 101 (1970). 2. E. Nakazawa, Chem. Phys. Lett. 56, 61 (1978). 3. E. Nakazawa, J. Lumin. 18/19, 272 (1979). 4. L. van Pieterson et al, J. Lumin. 91 177 (2000).

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Combinatorial chemical synthesis of scintillator materials James Powell*, Edith Bourret-Courchesne, Martin Boswell, Thomas F. Budinger, Stephen E. Derenzo, Christopher A. Ramsey, and David S. Wilson Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, U.S.A.

For the past 50 years, since scintillators started to gain recognition as technologically important materials, the pace of discovery has been limited by the slow pace of materials synthesis. Our approach is designed to accelerate the discovery process by developing a facility for the combinatorial synthesis of a large number of samples in microcrystalline form. The samples are not deposited as thin films and as such are not subject to interactions with a substrate. The samples are individually prepared by solid-state reactions in quantities of about one gram, sufficient for identifying new scintillation materials and making initial measurements of their scintillation properties. The semiautomated synthesis facility will be described in detail. It consists of a robotic dispenser for combining starting compounds and dopants in desired ratios and a computer-operated array of 48 atmosphere-controlled furnaces with differential thermal analysis to detect phase transitions. A signal, for example to alter the temperature program, can be sent to the furnace controller if a phase transition is detected. Synthesized samples are tracked by barcode, and all experimental data, starting from the weight of the initial charges prior to synthesis to the actual temperature program used for the synthesis, are automatically uploaded to a network-enabled central database that coordinates information among all components and provides distributed, user-friendly access to all collected data and analyses. Supported by DHS DNDO grant HSHQDC07X00170. * corresponding author e-mail: [email protected]

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Thin LSO-based scintillating mixed-crystal grown by liquid phase epitaxy for high resolution X-ray imaging A. Racka*, T. Martinb, M. Couchaudc, P.-A. Douissardb, A. Ceciliaa, A. Danilewskyd, T. Baumbacha a

Forschungszentrum Karlsruhe - ANKA, Postfach 3640, Karlsruhe, 76021, Germany b European Synchrotron Radiation Facility, BP 220, Grenoble, 38043, France c CEA Léti MINATEC, 17 rue des Martyrs, Grenoble, 38054, France d University Freiburg, Hermann-Herder-Str.5, Freiburg, 79104, Germany

A digital X-ray detector for high resolution synchrotron microtomography and -radiography is commonly based on projecting a luminescence image magnified via microscope optics onto a CCD chip. The use of higher magnifying optics leads to a decrease of the corresponding focal depth. Therefore, thin scintillating single-crystals are required in order to convert the X-ray beam as attenuated by the sample into visible light while avoiding an image blurring (e.g. around 5 µm active layer for submicron resolution and 20 µm for resolutions around 2 µm) [1]. As a consequence the stopping power and with that the detector’s efficiency decreases dramatically when working with higher resolutions. In recent years the number of imaging beamlines at third generation synchrotron light sources increased, leading to an ongoing demand and research for heavy scintillating materials available in thin active layers for microimaging. As one approach the CEA Léti together with the special detectors group of the European Synchrotron Radiation Facility (ESRF) used the liquid phase epitaxy technique to grow Lu3Al5O12 (LuAG) crystals (doped with Eu or Tb) and Gd3Ga5O12 (doped with Eu) as thin layers on top of non-doped substrates [2, 3]. Since the nineties LSO:Ce is known as a very fast and dense material highly suited for PET imaging [4] and was already suggested for the use in synchrotron imaging as well [1]. We present a continuation of the development by growing an LSO-based mixed-crystal (Lu2-xMxSiyGe1-yO5 where M is a rare earth element and x and y are in the range between 0.001 and 0.05) on top of a nondoped substrate. The mixed-crystals allows an improvement of the stopping power compared to other materials like LuAG or GGG by a factor of 2. A digital X-ray detector using that crystal has a high potential not only for synchrotron imaging than also for applications within the non-destructive testing market in general. This project SCINTAX is funded by the European Community as part of the Sixth Framework Programme (STRP 033 427). * corresponding author e-mail: [email protected] References 1. A. Koch et al., J. Opt. Soc. Am., vol. 15, no. 7, 1940-1951 (1998). 2. A. Koch et al., Phys. Med. Imag. Conf. Proc., SPIE vol. 3659, 170-179 (1999). 3. T. Martin et al., Proceedings SCINT2005, Kharkov, Ukraine (2005). 4. R. Nutt, C. L. Melcher, Revue de l'ACOMEN, vol. 5, no. 2, 152-155 (1999).

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Energy dissipation in impurity doped alkaline-earth fluorides E.Radzhabova*, M.Kirmb, A.Egranova, A.Nepomnyaschikha a

Vinogradov Institute of Geochemistry, Russian Academy of Sciences, Favorskii street 1a, P.O.Box 4019, 664033 Irkutsk, Russiaa b Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia

It was found from measurements of excitation spectra in vacuum ultraviolet region that some impurity like La, Y, Cd in BaF2 considerably reduces excitation intensity above band gap photon energies, while the reduction is not so much within exciton region [1]. It was concluded that the suppression of exciton emission is due to sequential trapping of charge carriers (free electron and holes) by impurity and following unradiative recombination at quenching impurity sites [1]. To generalize this conclusion we have measured the excitation spectra of CaF2 and SrF2 crystals doped with Cd. The excitation spectra of CaF2-Cd and SrF2-Cd at low temperatures were discouraging. There was no obvious reduction of excitation intensity in interband region. However we found a new emission which was excited in impurity region (below the exciton region). These new emission bands were found in CaF2-Cd and SrF2-Cd and not found in BaF2Cd crystals [2]. At tempeartures 50-80K in CaF2-Cd and 40-150K in SrF2-Cd new emission bands were quenched. Therefore, to exclude the influence of these bands, we measured the excitation spectra at room temperature. 2.0 0.5

1- CaF2-undoped 2- CaF2-Cd 1.5

1 - SrF2 - undoped

T=298K

0.4

2 - SrF2-0.27 mol. % CdF2

1.0

I, a.u.

I. a.u.

T=298K

1

0.3 1

0.2

0.5 0.1 2

0.0

8

10

12

14

16

2

18

0.0

20

8

E, eV

10

12

14

16

18

20

E, eV

The obvious reduction of excitation intensities in interband region were observed as in the case of BaF2 crystals (Fig.1). In conclusion, the main reason of suppression of exciton emission in doped alkaline-earth fluorides is the unradiative recombination of free electrons and holes on impurity sites. * Corresponding author: [email protected] References 1. E Radzhabov, M. Kirm , A Egranov , A Nepomnyachshikh, A .Myasnikova Proceeding of the SCINT 2005, Alushta, Crimea, Ukraine, September 19-23, 2005, 60-63 2. E.Radzhabov and M.Kirm J. Phys.: Condens. Matter 17, 5821 (2005)

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Influence of RE-doping on the scintillation properties of LSO crystals Guohao Ren*, Laishun Qin, Sheng Lu , Dongzhou Ding, Shangke Pan shanghai Institute of Ceramics, Chinese Academy of Sciences, No.215, Chengbeii Rd., Shanghai, 201800, China

Some rare earth (RE=Gd, Y, Sc) doped LSO:Ce (Lu2(1-x-0.5%)RExSiO5:0.5%Ce) crystals were grown by Czochralski method in an iridium crucible. The doping concentrations of RE were selected as 3.5%, 5.0%, and 10.0%. Samples with dimension of 17×17×2mm3 were cut and polished from the as-grown crystals. The segregation coefficients tested for Ce and Sc, Y and La in LSO crystals were 0.22, 0.55, 0.78 and 0.45. It was observed that Sc or Y doping nearly has no influence on the coefficient of Ce in LSO. Among these RE elements, La was the only element which increases the segregation coefficient of Ce in LSO from 0.22 to 0.37. As the radius of Ce3+(1.03 Å) is much bigger than that of Lu3+(0.85 Å)ions, it is not easy for Ce3+ to occupy the site of Lu3+ in the lattice. Sc3+ (0.732Å) and Y3+ (0.893Å) have the smaller or similar radius to Lu3+ ions, therefore, their doping will not expand the volume of the site which will occupied by Ce3+. However, La3+ with larger radius than Lu3+ ion, substitutes for Lu3+ and supply a big space for Ce in the structure. Thereby, more Ce ions can enter LSO crystal doped with La. The UV and X-ray excited emission spectra also exhibit similar characteristics, i.e. an asymmetrical emission band with a maximum intensity around 403nm for the excitation wavelength of 358 nm. The excitation spectrum taken at both emission of 403nm and 423nm has three weak excitation bands peaking at 298nm, 263nm and 230nm, in addition to the prominent excitation peak at 358nm. Its doublet structure of the spectra can be associated with the transition of the Ce3+ ions from the lowest 5d level to the two 4f ground states, 5d1→5F5/2 and 5d1→5F7/2. However, in the X-ray induced fluorescence spectra, Sc, Gd, or La doping results in the shifting of emission peak toward longer wavelength. Photoelectron yields for RE-doped LSO crystals were measured by comparing the position of the 511 KeV γ-ray peak from a 22Na source (20μCi). Compared with LSO:Ce crystal, Sc-doped LSO:Ce crystals has no significant change in light yield, but the energy resolution was worsen from 13.% to 15.9%. The light yield of Gd-doped LSO:Ce was improved, but the energy resolution was not as good as that of LSO:Ce crystal. This phenomenon can be explained from their structures and radius. YSO (Ce:Y2SiO5) and LYSO have the same C2/c structures as LSO, and the radius of Y is close to Lu. So the luminescent ion Ce3+ in these crystals has the equal local environment. YSO, LSO and their mixture crystal are spontaneously expected to have the same light output and decay time. It is also noticeable that the energy resolution fluctuates in a large range and double energy peaks appear in the energy spectrum of few LYSO samples. * corresponding author e-mail: [email protected]

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The promising detectors for nuclear planetology A.A. Rogozhin2, I. G. Mitrofanov1 , A. S. Kozyrev1, M.L.Litvak1, A.B.Sanin1, V. Tretyakov1 and N.P.Kuzmina,2 1 2

Space Research Institute (IKI), Russian Academy of Sciences, Moscow, 117997, Russia All-Russia Scientific Research Institute of Mineral Resources, 31, Staromonetny, Moscow,119017, Russia

The nuclear planetology as an avenue of space investigations is developing since 1960-s and has demonstrated several considerable achievements in recent years. A good example is the measurements of gamma-ray and neutron albedo from Mars and mapping of element composition of Mars surface by Gamma-Ray Spectrometer suite (GRS) on NASA’s Mars Odyssey orbiter. It includes high purity Ge sensor of gamma-rays, Neutron Spectrometer and High Energy Neutron Spectrometer (HEND). HEND was contributed by Federal Space Agency of Russia, it was developed in Space Research Institute, AllRussia Scientific Research Institute of Mineral Resources and other institutes. It integrates as one instrument a set of five sensors and the electronics boards. The set of sensors includes 3 proportional counters with 3He and scintillation detector. The stylben crystal is used to detect neutrons of energy >600 keV and CsI(Tl) scintillator served as anti-coincidence shield and detector for gamma-rays. With all these sensors HEND measures neutrons at broad energy range from epithermal (>0.4 eV) up to high energies about 15.0 MeV. The results of neutron flux measurements allowed to find out huge deposits of subsurface water ice at poleward regions on Mars, and also to evaluate seasonal deposition of atmospheric CO2 at northern and southern hemispheres of Mars. The scientific, technical and technological experience obtained during realization of HEND project has allowed to proceed in developing several future instruments for nuclear planetology. The scintillation detectors for these instruments are currently under design. For detection of high energy neutrons these new sensors are based on stylben (as for HEND) and plastic scintillators. For detection of gamma-rays new innovative scintillators LaBr3(Ce) of various dimensions (up to about 3” diam.x3” height) are used. The first in the line is the Lunar Exploration Neutron Detector LEND for NASA’s “Lunar reconnaissance orbiter”, which launch is scheduled at October, 2008. The primary goal of Russian contributed instrument is to search for hydrogen and water resources on the Moon and to test for water ice deposits within so-called «cold traps» in permanently shadowed polar craters. LEND also will measure neutron component of the radiation background, which is important for future manned flights to the Moon. The next instrument named Neutron and gamma-ray spectrometer HEND (NS–HEND) is currently under development for Russian interplanetary mission “Fobos-grunt” planned for launch to Mars in 2009. The latest in the line is Mercury Gamma-ray and Neutron Spectrometer (MGNS), which is the Russian contribution for ESA’s BepiColombo mission to Mercury at August of 2013. Corresponding author: [email protected]

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EPR of intrinsic radiation defects in LiYF4 crystal Andris Fedotovsa*, Uldis Rogulisa, Lauris Dimitrocenkoa a

Institute of Solid State Physics, University of Latvia, Kengaraga street 8, Riga, LV-1063, Latvia

LiYF4 scheelite crystals are considered as valuable materials suitable for applications as scintillators and laser medium material [1]. Recent reports of optical and electron paramagnetic resonance spectroscopy studies of these crystals show possibility that various types of intrinsic defects such as VK centre can be created by ionizing radiation [2, 3]. In current research electron paramagnetic resonance (EPR) spectra of a nominally pure LiYF4 crystal were investigated after X-ray irradiation at room temperature (RT). The orientation of its optical axis c has been determined by means of optical polarization and the angular dependencies of the EPR spectra were measured in ab and ac planes. The obtained results showed the presence of a radiation-induced defect which is stable at RT. The broad EPR band of this defect in the X-microwave range is found to be structureless at RT. Basing on the estimated g-values, we suggest that the EPR spectra of the observed radiation defect could belong to an electron trap center. The structure of the spectrum could be resolved by measurements at 77 K. The spectra exhibit strong angular dependence, which is explained by the g-anisotropy and hyperfine interaction of the unpaired electron spin with two neighbouring fluorine nuclei. * corresponding author e-mail: [email protected] References 1. C. M. Combes, P. Dorbenos, C. W. E. van Eijik, C. Pedrini, H.W. den Hartog, J.Y. Gesland, P.A. Rodnyi, J. Lumin. 71, 65 (1997). 2. G. M. Renfro, L. E. Halliburton, W. A. Sibley, R. F. Belt , J. of Phys. C. 13, 1941 (1980). 3. M. Herget, A. Hofstaetter, A. Scharmann, phys. stat. sol. (b), 127, K83 (1985).

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Luminescence and scintillation characteristics of the SrCl2 single crystal for the neutrinoless β+/EC decay search Gul Rooha, Heedong Kanga, H.J. Kima*, H. Parka, Sih-Hong Dohb a

Kyungpook Nat’l University, Daegu, 702-701, KOREA b Pukyung Nat’l University, Busan, 608-737, KOREA

The aim of this study is to develop scintillation crystals for the study of neutrinoless β+/EC decay process. The Sr-84 isotope is one of the potential candidates for the neutrinoless β+/EC decay process, its Q-value is 1.7868 MeV and natural abundance is 0.56%. None of the scintillation crystal containing strontium element up till now was used for the study of neutrinoless β+/EC decay process. In general our crystal growth program includes studies of starting material preparation, growth procedures and characterization of grown crystals. We have grown a SrCl2 single crystal by using the Czochralski method. The cylindrical shape of the SrCl2 crystal was cut into the dimensions of Φ2×1.5 cm3. Luminescence property of the crystal was studied under the excitation by the UV source at room temperature. The scintillation properties were studied using various gamma ray sources and an alpha source. The scintillation properties such as energy resolution, light output, linearity and decay time are presented. In particular, the α/β light ratio [1] and the possibility of a pulse shape discrimination between α and γ quanta using Am-241 alpha source have been studied. This work was supported by the SRC/ERC program of MOST/KOSEF (R11-2000-06702001-1). * corresponding author e-mail [email protected] References 1. P. Belli, R. Bernabei, R. Cerulli, C.J. Dai, F. A. Danevich, A. Incicchitti, V. V. Kobychev, O. A. Ponkratenko, D. Prosperi, V. I. Tretyak, Yu. G. Zdesenko, Nucl. Instr. & Meth. A498, 352 (2003).

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Intrinsic luminescence and band structure of Lu2SiO5 and Y2SiO5 crystals Evgeniy Shlygina*, Vladimir V. Mazurenkoa, Vladimir Ivanova, Vladimir Pustovarova, Michail Kuznetsovb, Alexander Kruzhalova, and Boris Shulgina a

Ural State Technical University, Mira St.19, Yekaterinburg, 620002, Russian Federation Institute of Solid State Chemistry Ural Branch of RAS, Pervomaiskaya St. 91, Yekaterinburg, 620219, Russian Federation

b

In the present work we have performed VUV-study of an intrinsic luminescence in scintillation oxyorthosilicate crystals Lu2SiO5 and Y2SiO5. An existence of self-trapped excitons (STE) is confirmed with a various degree of evidence for binary oxides α-SiO2, Y2O3 and in recent research for Lu2O3 [1]. In this connection, the research of electronic excitations (EEs) in relevant complex oxides would be interesting. Photoluminescence spectra (2-6 eV), photoluminescence excitation spectra (4-35 eV), reflection spectra and luminescence decay kinetics have been measured at the SUPERLUMI station of HASYLAB (DESY, Hamburg). Low-temperature luminescence bands peaked at 3.7 and 4.6 eV in Lu2SiO5 and at 3.7 eV in Y2SiO5 (time-resolvedly subdivided into two bands 3.5 and 3.8 eV) are suggested to be an intrinsic luminescence and ascribed to the radiation decay of STE. In addition we have accomplished comparative ab initio electronic structure calculations by the tight-binding linearized muffin-tin orbital (TBLMTO-ASA) method within local density approximation (LDA) for both lattices. The bottom of the conduction band in the crystals predominantly consists of d electronic states of heavy cations. In lutetium oxyorthosilicate the density of states for oxygen bounded with silicon differs from those for oxygen which hasn’t silicon at the nearest neighbors. Early similar situation was exhibited for it counterpart in yttrium oxyorthosilicate [2]. The narrow bandwidth distinctive peculiarity of 4f-Lu states below band gap for Lu2SiO5 has been confirmed. The results of our LDA-calculation are in good agreement with XPS spectra which were also measured in this work at X-ray photoelectron spectrometer ESCALAB MK II. The contribution of heavy cation sublattice in EEs relaxation processes of oxyorthosilicates is discussed. This work was partially supported by the RFBR (grant No. 05-02-16530) and INTAS Ref. Nr 04-83-3230. * corresponding author e-mail: [email protected] References 1. D. W. Cooke et al. J. Lumin. 106, 125-132 (2004). 2. W. Y. Ching et al. Phys. Rev. B 67, 245108 (2003).

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Electronic structure of Pb- and non-Pb based phosphate scintillators D.J. Singh*, G.E. Jellison, Jr. and L.A. Boatner Materials Science and Technology Division and Center for Radiation Detection Materials and Systems, Oak Ridge National Laboratory, Oak Ridg,e TN 37831

Efficient scintillators for radiation detection are usually based on single crystals. However, the requirement for high quality, uniform crystals limits the size of detectors. Glasses are much more easily scaled to large sizes, and can be molded into desired shapes, and as such, are used in a number of applications. However, existing glass scintillators have lower light yields than the crystalline materials and this limits their applications. One avenue for improving the performance of glass scintillators is to explore new glass forming compositions related to existing scintillators. Challenges to developing new glass scintillators include finding appropriate activators, and obtaining good energy transfer to the activator sites in glasses, despite the presence of localized electronic states near band edges. Activated orthophosphate crystals, such as LuPO4, are commonly used in scintillators for gamma and x-ray detection. It has been shown that there are related Pb containing phosphates, based on Pb2P2O7 that can be grown either as crystals or glasses, and that these materials readily form and have high optical quality, chemical stability, and radiation hardness. Furthermore, they have a very high density, due to the high Pb content, and a flexible chemistry that is amenable to doping with various rare earths and other potential activators. Here the electronic structures of Pb and non-Pb containing phosphates, specifically Pb3(PO4)2, Pb2P2O7, ScPO4, YPO4, and LuPO4, are compared using a combination of density functional calculations and optical measurements. We find that the characteristic difference between these two classes is that the band gaps in the Pb containing materials are significantly lower because of the presence of Pb 6p derived bands in the gap between the valence bands and the P-O antibonding states. This may be favorable from the point of view of energy transfer in scintillator applications of Pb-based phosphates. However, it also suggests that different activators than those used in other phosphate scintillators may be useful to increase the efficiency. This work as supported by the Department of Energy, NA22. * [email protected] References 1. D.J. Singh, G.E. Jellison, Jr., and L.A. Boatner, Phys. Rev. B 74, 155126 (2006).

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Radiative decay of electronic excitations in ZrO2 nanocrystals and macroscopic single crystals Krisjanis Smitsa*, Larisa Grigorjevaa, Donats Millersa, Janusz D.Fidelusb, Witold Lojkowski a

Institute of Solid State Physics, 8 Kengaraga Str., Riga, LV-1063,Latvia Institute of High Pressure Physics, 29/37 Sokolowska Str., Warszawa, 01-142, Poland

b

The luminescence and transient absorption were studied for yttrium stabilized ZrO2 macroscopic size single crystal under pulsed electron beam irradiation. The luminescence spectrum and decay kinetics observed for macroscopic single crystal were compared with those for yttrium stabilized ZrO2 nanocrystals and differences were found. The luminescence bands below ~ 4 eV were shown to be defect related for both kinds of samples. The number of defects strongly affect the luminescence. If the number of defects increases, the number of luminescence centers increases also. On the other hand, it was observed that the increase of defects number strongly suppreses the energy transfer to the luminescence centres. It was suggested the luminescence comes from electronic excitations perturbed by defects, e.g., distorted Zr – O bonds, not from the decay of defect excited state. The transient absorption measurements shown that under pulsed electron beam irradiation even in macroscopic single crystal a large number of defects was recharged. The comparision of transient absorption relaxation and luminescence decay kinetics gives an evidence that the relaxation of transient absorption was not followed by luminescence. The centers responsible for luminescence and centers responsible for transient absorption were not the same. The comparision of luminescence spectra shown that in the ZrO2 macroscopic single crystal a few centers account for luminescence whereas in ZrO2 nanocrystals a relative large number of slightly different luminescence centers are. Two well resolved components were observed in the ZrO2 luminescence decay in both kinds of crystals. However the decay kinetics differ – in the nanocrystals dominant is contribution from fast component, whereas in macroscopic single crystal from slow componet. It is suggested that in nanocrystals large fraction of luminescence centers might be perturbed due to its specific position. Possible models of luminescence centers and recombination proceses will be discussed. Acknowledgments – the authors are thankfull to the Latvian Council of Science ( grants 05.1720 and 05.0026) and ESF for financial support. * corresponding author e-mail: [email protected]

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Brighter and faster LSO:Ce M. A. Spurrier,a* P. Szupryczynski,a,b A. A. Carey,b C. L. Melchera a

Scintillation Materials Research Center, University of Tennessee, Knoxville, TN 37996, USA b Siemens Medical Solutions USA Molecular Imaging, Knoxville, TN 37932, USA

In addition to desirable physical properties including a density of 7.4 g/cm3, an effective atomic number of 66, and no hygroscopicity, Lu2SiO5:Ce has well-known scintillation properties of ~33,000 photons/MeV, an emission peak near 420 nm, and a decay time of 42-44 ns. These scintillation properties are achieved with Ce doping concentrations roughly in the range of 0.05 to 0.5 atomic per cent relative to Lu. These properties make Lu2SiO5:Ce a widely used scintillator in positron emission tomography, in particular. We have found that both the light output and decay time may be improved by a combination of optimized crystal growth atmosphere and co-doping with divalent cations such as Ca. Scintillation light output approaching 40,000 photons/MeV has been achieved as well as scintillation decay time as short as 28 ns with no long components. The relationship between growth conditions, dopant concentration, decay time, and light output is well defined, thus allowing one to reliably “tune” the crystal to the desired combination of light output and decay time. Possible explanations of the underlying mechanism are being explored and include compensation of oxygen vacancies, alteration of the relative occupancies of the cerium lattice sites, and suppression of trapping centers. In addition to higher count-rate capability and better coincidence timing, the improved decay time is expected to be particularly advantageous for time-of-flight positron emission tomography. Also, phoswich detectors comprising “standard” LSO (~42 ns decay time) and “fast” LSO (~28 ns decay time) become an attractive alternative to typical phoswich designs that often suffer from problems of mismatched light outputs and indices of refraction or the absorption of one scintillator’s light by the other. * corresponding author e-mail: [email protected]

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Novel trends in development of A2B6-based scintillators N. Starzhinskiy*, B. Grinyov, L. Gal’chinetskii, V. Ryzhikov, V. Silin Institute for Scintillation Materials of National Academy of Science of Ukraine, 60 Lenin Ave., Kharkiv 61001, Ukraine

Recent achievements have been reviewed in preparation, radiation physics and application of zinc selenide and other chalcogenide scintillators (CS) based on A2B6 compounds, with special attention paid to the formation mechanisms of the luminescence centers and energy transfer processes related to relaxation of the exited states. It has been shown that, among A2B6 compounds, zinc selenide crystals are, due to their physical and chemical properties, the best optimized crystalline matrices for creation of luminescent materials with output parameters characterizing them as efficient scintillators (high light output, fast response, high radiation stability, very low afterglow level, good spectral matching with Si-photoreceivers, etc.). The first successful experience in this direction was the development of ZnSe(Te) scintillators (CS-I), shown to be one of the most suitable materials for low-energy X-ray digital radiography. At present, the list of A2B6-based scintillators has been extended by inclusion of new О- and Сd-activated zinc selenide crystals (СS-II), which are characterized, as compared with CS-I, by substantially shorter decay time τ and even lower afterglow level η (see Table). Table. Comparison of the basic parameters of CS-I, CS-II and CsI(Tl) crystals Crystal \ Parameter Luminescence maximum λmax, nm Afterglow, η, after 5 ms, % Decay time, τ, μs Light yield, photons/MeV -1 Absorption coefficient, α, cm Radiation stability, rad

CS-I (“Slow”-type) ZnSe(Te), ZnSe(Cd,Te) 630-640 < 0.2 -9 ≤ 5·10 ; 50-150 up to 76000 0.1-0.2 5⋅108

CS-II (“Fast”-type) ZnSe(O), ZnSe(Cd), ZnSe(O,Al) 600-620 < 0.01 -9 ≤ 5·10 ; 1-3 up to 63500 0.1-0.15 2⋅108

CsI(Tl) 550 3-5 1 55000 10 keV) has tremendous potential for future discoveries. A mission dedicated to such a survey will explore astrophysical extremes and enable studies ranging from a survey of point-like objects to investigations of spatially extended ones. A new approach to such a survey is to utilize the Moon as an occulting disk. Temporally modulated sources, which rise and set along the lunar limb, can then be reconstructed in both the spatial and spectral domains. The Lunar Occultation Observer (LOCO) mission concept is based on this Lunar Occultation Technique (LOT) and represents a viable option for a hard X-ray sky survey. LOCO detectors will utilize the inorganic scintillator LaBr3 as the fundamental detection medium. The benefit of this approach is that it requires no advanced imaging optics or masks, and can therefore achieve high source sensitivity, as well as excellent spatial and spectral resolutions, in a cost effective deployment. We present the motivating factors for the LOT, outline developmental details and simulation results, as well as give preliminary estimates for source detection sensitivity.

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CeBr3 scintillator development for space missions W. Drozdowskia*, P. Dorenbosa, A.J.J. Bosa, A. Owensb, F.G.A. Quaratib a

Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands b European Space Agency, ESTEC SCI-A, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

CeBr3 crystals have been studied as potential gamma ray spectrometers for the future European Space Agencies (ESA) missions to solar planets. X-ray excited emission spectra, pulse height spectra and scintillation time profiles have been recorded as function of temperature between 77 and 600 K. In addition, we have investigated the influence of exposing CeBr3 to various doses of gamma rays from a strong 60Co source on its scintillation performance. We have also measured the yield proportionality with gamma energy and self-activity of this material before and after gamma irradiation. Small irregular samples of CeBr3 show a photoelectron yield of 17000 phe/MeV and an energy resolution of 3.9% at 662 keV. For comparison, similar scrap samples of LaBr3:5%Ce, the material proposed for the ESA BepiColombo mission to Mercury [1], display a yield and a resolution of 25000 phe/MeV and 2.5%, respectively [2]. However, the growth technology of CeBr3 has not been optimized yet and there may still be room for improvement; note that Shah et al. have reported a resolution of 3.2% for