@article{e5eaa0bdc33347638dd532ad876330cf,
title = "High Efficiency CsI(Tl)/HgI2 Gamma Ray Spectrometers",
abstract = "CsI(Tl)/HgI2 gamma-ray spectrometers have been constructed using 0.5” diameter detectors which show excellent energy resolution: 4.58% FWHM for 662 keV 137Cs gamma-ray photons [1]. Further efforts have been focused on optimization of larger size (≥1” 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 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”, bottom-1”, 2” high) CsI(Tl) scintillator coupled with a 1” HgI2 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.",
author = "Wang, {Y. J.} and Patt, {B. E.} and Iwanczyk, {J. S.} and Cherry, {S. R.} and Y. Shao",
note = "Funding Information: Gamma-ray spectrometers consisting of HgI2 PDs coupled with CsI(n) scintillators have demonstrated excellent energy resolutions (4.58% FWHM for 662 keV I3{\textquoteright}Cs gamma-ray photons for a 0.5” diameter PD). In order to make higher efficiency gamma-ray scintillation detectors, efforts have focused on a) fabricating high quality, large size (21” diameter) Hg12 PDs, b) minimizing electronic noise of the amplification system, and c) optimizing the scintillatorRD configurations. Monte Carlo simulations showed that if a small PD is to be coupled to a larger scintillator, the cone shaped scintillator results in better light collection than a larger diameter cylinder. Experimental results showed agreement with the Monte Carlo theoretical prediction. A large cone shaped (top-2{\textquoteright}: bottom-l”, 2” high) CsI(Tl) scintillator, coupled with a 1” Hg12 PD, has been measured. The FWHM energy resolution for 662 keV was 5.57%. This result verified that Hg12 PDs, combined with large volume scintillators can be effective as high efficiency gamma-ray spectrometers. In addition to their high efficiency and excellent energy resolution, the other advantages of Hg12 detectors (compact sizes, ruggedness, no cryogenic requirements, etc.) open a broad fiture for the use of these units in many applications for CsI(Tl) scintillator spectro~PY* The research work described in this paper was supported by the National Aeronautics and Space AdmiNst~ation, Contract NAS7-1204 and Department of Energy Contract DE-FG03-94ER81687. The authors wish to acknowledge Dr. Albert Metzger (Jet Propulsion Laboratory) for valuable comments and suggestions regarding this work. In addition we wish to thank Ms. Fanny Riquelme and Ms. Xin Qin for the fabrication of the HgI2 photodetectors and Mr. Wayne Schnepple for assistance in preparation of this paper.",
year = "1995",
month = aug,
doi = "10.1109/23.467906",
language = "English (US)",
volume = "42",
pages = "601--605",
journal = "IEEE Transactions on Nuclear Science",
issn = "0018-9499",
publisher = "Institute of Electrical and Electronics Engineers Inc.",
number = "4",
}