TDR BEta-deLayEd Neutron detector Universitat Politècnica de Catalunya, Barcelona, Spain F. Calviño, G. Cortés, A. Riego, R. Caballero-Folch, C. Pretel, Ll. Batet, A. Torner, A. Poch, M.B. Gómez-Hornillos, V. Gorlychev

Instituto de Física Corpuscular, CSIC-Universidad Valencia, Valencia, Spain J.L. Taín, J. Agramunt, A. Algora, C. Domingo-Pardo

GSI, Darmstadt, Germany I. Dillmann, M. Marta

CIEMAT, Madrid, Spain D. Cano-Ott, T. Martínez, A. García

January 22, 2014 Abstract The BEta-deLayEd Neutron (BELEN) detector is a 4π neutron detector based on 3 He counters embedded in a polyethylene matrix. This detector will be part of the DESPEC experiment at FAIR and will be used to measure beta-delayed neutron emission probability (Pn ) together with a beta detector. This report includes the details about the configuration of the detector for FAIR and the design and construction of a prototype of the neutron detector that has already been used at JYFL and GSI.

Contents 1 Introduction and overview

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2 Physics requirements for the system

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3 Summary of Monte Carlo simulations 3.1 Layout of the neutron detector . . . . 3.2 Neutron moderation in polyethylene . 3.3 3 He pressure analysis . . . . . . . . . . 3.4 Counter length analysis . . . . . . . .

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4 Previous tests and prototypes 4.1 Preliminary tests with a 252 Cf source . . . . . . . . . . . . . . 4.1.1 First preliminary test . . . . . . . . . . . . . . . . . . 4.1.2 Full detector prototype test . . . . . . . . . . . . . . . 4.2 Previous prototypes . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 BELEN-20 at IGISOL Trap in JYFL (2009) . . . . . . 4.2.2 BELEN-20 updated at IGISOL Trap in JYFL (2010) . 4.2.3 BELEN-30 at GSI (2011) . . . . . . . . . . . . . . . . 4.2.4 Summary of previous prototypes . . . . . . . . . . . . 4.3 Summary of detector results: BELEN-48 . . . . . . . . . . . .

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5 Technical specifications and design details 5.1 Electronics and Triggerless Data Acquisition System . . . . . . . . . . . . . . . . 5.2 Detector construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Background and shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6 Radiation environment and safety issues

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7 Production, quality assurance and acceptance tests

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8 Calibration with test beams

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9 Civil engineering and cave

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10 Installation procedure and logistics

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11 Time schedule table and milestones

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Annex A. Budget and funding

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List of Tables 1 2 3 4 5 6 7 8 9 10 11 12

Summary of the main characteristics of the proportional counters used at the tests. Experimental and simulated (MCNPX) detection efficiency of the counters [12]. . Configuration details of the BELEN-20 prototype. . . . . . . . . . . . . . . . . . Configuration details of the updated BELEN-20 prototype. The central block with a diameter of 130 mm while all the rest of 110 mm. . . . . . . . . . . . . . . Configuration details of the BELEN-30 prototype. . . . . . . . . . . . . . . . . . Main features of previous experiments . . . . . . . . . . . . . . . . . . . . . . . . Characteristics of the available 3 He counters. . . . . . . . . . . . . . . . . . . . . Polyethylene properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Configuration details of BELEN-48 detector. . . . . . . . . . . . . . . . . . . . . Summary of BELEN-48 detection MCNPX efficiency and planarity for different energy ranges up to 2 MeV and 5 MeV. . . . . . . . . . . . . . . . . . . . . . . . BELEN-48 list of electronic components. . . . . . . . . . . . . . . . . . . . . . . . Possible validation reactions. Laboratory frame projectile energy Eproj , average neutron energy , and width of the neutron energy distribution ∆En [18]. .

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List of Figures 1 2 3 4

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Decay scheme of a beta-delayed neutron emission. . . . . . . . . . . . . . . . . . Deposited energy in 3 He (keV). . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross section for reaction 3 He(n,p)3 H. Plot taken from [8] . . . . . . . . . . . . . Summary table of neutron flux in the polyethylene block for different source energies and neutron propagation times. Front view. Dimensions of x and y-scale are in cm. The colour shades indicate the density of neutrons with an energy below 10−7 MeV, red shows the highest density (>200 neutrons/cm2 ) and light blue the lowest (200 neutrons/cm2 ) and light blue the lowest (200 neutrons/cm2 ) and light blue the lowest (