3D Position Sensitive CdZnTe Spectrometers Using 3rd-Generation VAS/TAT Readout Electronics

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3D Position Sensitive CdZnTe Spectrometers Using
3rd-Generation VAS/TAT Readout Electronics

• Feng Zhang, Zhong He, Glenn F. Knoll,
• David K. Wehe, James E. Berry
• Department of Nuclear Engineering and
  Radiological Sciences
• The University of Michigan
• Acknowledgements
• Department of Energy, NA-22 Office

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What is a 3-dimensional position sensitive
semiconductor detector?
Incident radiation (?, charge particle, etc.)
(?E,x,y,z)1
(?E,x,y,z)2
(?E,x,y,z)3
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How to achieve 3-D position sensing?
x
?
y
1.27 mm pitch
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Second generation 3-D CdZnTe detectors can
provide (E,x,y,z)i of multiple ?-ray interactions
a1
a2
C

?t2 ? z2
?t1 ? z1
Triggers
Time
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System configuration
Ideas ASA
eV-Products (2001)
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Energy spectrum of 137Cs from single-pixel events
(Detector 2.2, from entire 1.51.51.0 cm3
volume) (VC -2200 V VG -60 V Time 40 h
uncollimated source room temperature)
662 keV
After correction for gain variation between
channels, temperature shift, effects of electron
trapping, weighting potential and non-linearity
of ASIC
FWHM 0.93 (6.16 keV)
137Cs 32 keV K x-ray
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Energy spectrum of 137Cs from single-pixel events
(Detector 2.3, from entire 1.51.51.0 cm3
volume) (VC -1400 V VG -45 V Time 40 h
uncollimated source room temperature)
662 keV
137Cs 32 keV K x-ray
FWHM 0.76 (5.03 keV)
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Energy spectrum of 137Cs from two-pixel events
( Detector 2.3 1.51.51.0 cm3 VC -1400 V
VG -45 V Time 40 h)
662 keV
FWHM 1.23 (8.14 keV)
Higher peak-to-Compton ratio
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Energy resolution distribution (single-pixel
events)
(Detector 2.2 137Cs 662 keV VC -2200 V VG
-60 V Time 40 h)
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Energy resolution distribution (single-pixel
events)
(Detector 2.3 137Cs 662 keV VC -1400 V VG
-45 V Time 40 h)
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Electron mobility-lifetime products distribution
(Detector 2.2)
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Electron mobility-lifetime products distribution
(Detector 2.3)
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Advantages of 3-D detectors

• Single polarity charge sensing ? Overcome the
  effects of severe hole trapping
• Depth sensing ? Correct electron trapping
• 3-D coordinates of interactions ? Mitigate the
  effects of material non-uniformity to the scale
  of position resolution
• Minimum electronic noise (leakage current
  detector capacitance are shared among pixels)
• Excellent energy resolution - 0.76 FWHM at 662
  keV for single-pixel events (uncollimated, room
  temperature)
• ?-ray imaging
• Detector physics (increase sensitivity by
  recognizing signatures of radiation interactions)
• Detector operation can be simple for end users
• Further development
• Larger detectors
• Miniaturize ASIC (for tile-able systems)

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Spectrum for all 1, 2 and 3-pixel events
( Detector 2.3 1.51.51.0 cm3 VC -1400 V
VG -45 V Time 40 h)
662 keV
FWHM 0.93 (6.16 keV)