Overview • Sensor • x-ray detection: direct & indirect • silicon as x-ray detector and the photodiode • THE CCD • sidewards depletion and the SDD • Electronics • charge readout – aka “the amplifier” • speed, noise and power compromise • Information Generation Rate and Figure of Merit • Camera • Hybrid Pixel Detectors • photon counting vs integrating imagers • a word on crosstalk and scaling
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X-ray cameras : direct and indirect detection
direct conversion detector uses photoeffect in silicon to detect x-rays
indirect conversion detector uses scintillation to convert x-rays into “visible” light and then detect this light with a silicon sensor
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X-ray cameras : direct and indirect detection
x-ray photon
x-ray photon
visible light
electronic signal electronic signal 4
direct conversion in silicon
photoeffect Compton
scattering
• • •
below ca. 40keV photoeffect dominates in Silicon Silicon is an indirect semiconductor Silicon bandgap: 1.11eV
pair production
1.11eV
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M.N. Mazziotta, Electron–hole pair creation energy and Fano factor temperature dependence in silicon NIMA 584 (2008) R. Hartmann, The quantum efficiency of pn-detectors from the near infrared to the soft X-ray region, NIMA 439 (2000)
electron hole pair creation energy and Fano factor
140K
300K
1 electron per 3.65eV
1 photon = 1 electron
for x-rays there is a variance in the numbers of electrons generated: