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Title: High efficiency CsI(Tl)/HgI{sub 2} gamma ray spectrometers

Abstract

CsI(Tl)/HgI{sub 2} gamma-ray spectrometers have been constructed using 0.5 inch diameter detectors which show excellent energy resolution: 4.58% FWHM for 662 keV {sup 137}Cs gamma-ray photons. Further efforts have been focused on optimization of larger size ({ge} 1 inch diameter) detector structures and improvement of low noise electronics. In order to take full advantage of scintillation detectors for high energy gamma-rays, larger scintillators are always preferred for their higher detection efficiencies. However, the larger capacitance and higher dark current caused by the larger size of the detector could result in a higher FWHM resolution. Also, the increased probability of including nonuniformities in larger pieces of crystals makes it more difficult to obtain the high resolutions one obtains from small detectors. Thus for very large volume scintillators, it may be necessary to employ a photodiode (PD) with a sensitive area smaller than the cross-section of the scintillator. Monte Carlo simulations of the light collection for various tapered scintillator/PD configuration were performed in order to find those geometries which resulted in the best light collection. According to the simulation results, scintillators with the most favorable geometry, the conical frustum, have been fabricated and evaluated. The response of a large conical frustum (top-2more » inch, bottom-1 inch, 2 inch high) CsI(Tl) scintillator coupled with a 1 inch HgI{sub 2} PD was measured. The energy resolution of the 662 keV peak was 5.57%. The spectrum shows much higher detection efficiency than those from smaller scintillators, i.e., much higher peak-to-Compton ratio in the spectrum.« less

Authors:
; ;  [1]; ;  [2]
  1. Xsirius, Inc., Camarillo, CA (United States)
  2. Univ. of California School of Medicine, Los Angeles, CA (United States). Crump Inst. for Biological Imaging
Publication Date:
OSTI Identifier:
129192
Report Number(s):
CONF-941061-
Journal ID: IETNAE; ISSN 0018-9499; TRN: IM9550%%560
Resource Type:
Journal Article
Resource Relation:
Journal Name: IEEE Transactions on Nuclear Science; Journal Volume: 42; Journal Issue: 4Pt1; Conference: Institute of Electrical and Electronic Engineers (IEEE) nuclear science symposium and medical imaging conference, Norfolk, VA (United States), 30 Oct - 5 Nov 1994; Other Information: PBD: Aug 1995
Country of Publication:
United States
Language:
English
Subject:
44 INSTRUMENTATION, INCLUDING NUCLEAR AND PARTICLE DETECTORS; GAMMA SPECTROMETERS; DESIGN; SCINTILLATOR-PHOTODIODE DETECTORS; PERFORMANCE; CESIUM 137; CESIUM IODIDES; MERCURY IODIDES

Citation Formats

Wang, Y.J., Patt, B.E., Iwanczyk, J.S., Cherry, S.R., and Shao, Y. High efficiency CsI(Tl)/HgI{sub 2} gamma ray spectrometers. United States: N. p., 1995. Web. doi:10.1109/23.467906.
Wang, Y.J., Patt, B.E., Iwanczyk, J.S., Cherry, S.R., & Shao, Y. High efficiency CsI(Tl)/HgI{sub 2} gamma ray spectrometers. United States. doi:10.1109/23.467906.
Wang, Y.J., Patt, B.E., Iwanczyk, J.S., Cherry, S.R., and Shao, Y. Tue . "High efficiency CsI(Tl)/HgI{sub 2} gamma ray spectrometers". United States. doi:10.1109/23.467906.
@article{osti_129192,
title = {High efficiency CsI(Tl)/HgI{sub 2} gamma ray spectrometers},
author = {Wang, Y.J. and Patt, B.E. and Iwanczyk, J.S. and Cherry, S.R. and Shao, Y.},
abstractNote = {CsI(Tl)/HgI{sub 2} gamma-ray spectrometers have been constructed using 0.5 inch diameter detectors which show excellent energy resolution: 4.58% FWHM for 662 keV {sup 137}Cs gamma-ray photons. Further efforts have been focused on optimization of larger size ({ge} 1 inch diameter) detector structures and improvement of low noise electronics. In order to take full advantage of scintillation detectors for high energy gamma-rays, larger scintillators are always preferred for their higher detection efficiencies. However, the larger capacitance and higher dark current caused by the larger size of the detector could result in a higher FWHM resolution. Also, the increased probability of including nonuniformities in larger pieces of crystals makes it more difficult to obtain the high resolutions one obtains from small detectors. Thus for very large volume scintillators, it may be necessary to employ a photodiode (PD) with a sensitive area smaller than the cross-section of the scintillator. Monte Carlo simulations of the light collection for various tapered scintillator/PD configuration were performed in order to find those geometries which resulted in the best light collection. According to the simulation results, scintillators with the most favorable geometry, the conical frustum, have been fabricated and evaluated. The response of a large conical frustum (top-2 inch, bottom-1 inch, 2 inch high) CsI(Tl) scintillator coupled with a 1 inch HgI{sub 2} PD was measured. The energy resolution of the 662 keV peak was 5.57%. The spectrum shows much higher detection efficiency than those from smaller scintillators, i.e., much higher peak-to-Compton ratio in the spectrum.},
doi = {10.1109/23.467906},
journal = {IEEE Transactions on Nuclear Science},
number = 4Pt1,
volume = 42,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 1995},
month = {Tue Aug 01 00:00:00 EDT 1995}
}
  • Gamma-ray spectrometers using mercuric iodide (HgI{sub 2}) photodetectors (PDs) coupled with CsI(Tl) scintillators have shown excellent energy resolutions and high detection efficiency at room temperature. Additionally HgI{sub 2} semiconductor PDs allow for extreme miniaturization of the detector packaging compared with photomultiplier tube (PMT) based detectors. These advantages make possible the construction of a new generation of hand-held gamma-ray spectrometers. Studies of detector optimization for this application have been undertaken. Several contact materials including hydrogen and semi-transparent metal films have been evaluated and compared for their performances and long term stability. In order to provide higher gamma-ray detection efficiency (i.e., largermore » scintillator volume), but without causing significant degradation of the excellent response achieved with the matched scintillator/PD interface, the scintillator/PD configuration has been studied. A Monte Carlo simulation model has been developed so that the spectral shape can be predicted for various scintillator shapes and surface treatments.« less
  • The utilization of NaI(Tl) scintillators as a high efficiency, fast neutron monitor, through the reaction /sup 127/I(n,n')/sup 127/I/sup 4/(E/sub x/ = 57 keV)/sup 127/I(E/sub x/ = 0), has been established. The total gamma ray production cross sections for the 57 keV gamma ray in /sup 127/I by inelastic scattering of 3 MeV and 14 MeV neutrons are 0.43 +- 0.04 b and 0.28 +- 0.03 b respectively. Temperature and count rate limitations on this utilization have been determined. The same reaction should allow HgI/sub 2/ semiconductor gamma ray detectors with intrinsic energy resolution potentially far superior to NaI(Tl) to bemore » utilized to monitor fast neutrons.« less