Year
1995
Abstract
A novel new semiconductor photodetector has been developed which utilizes large mercuric iodide photodetectors coupled to highly optimized CsI(Tl) scintillators for gammaray spectroscopy. With this new detector technology we have achieved energy resolution superior to that of any other scintillation detector. Furthermore, gamma probes based on the new HgI2/CsI(TI) detector can be highly miniaturized offering improved portability. A 1/2-inch diameter HgI2 photodetector coupled with a 1/2-inch diameter by 1/2-inch high right-rectangular scintillator produced energy resolution of 4.58% FWHM for 137Cs (662 keV). This is perhaps the best result ever reported for room temperature scintillation spectroscopy. Evaluation of a prototype device with similar performance has been conducted at Los Alamos using Pu and U standard samples. Recently, Monte-Carlo simulations have been performed for co-optimization of the gamma-collection efficiency and light collection efficiency of the scintillator/photodetector pairs resulting in a new tapered scintillator geometry. Energy resolution of 5.69% FWHM at 662 keV was obtained for a 1\" diameter photodetector coupled to a two-inch long conical CsI(Tl) scintillator; with dimensions: 1-inch diameter at the top tapered to 2-inch diameter at the bottom. The long term stability of the technology has been verified. Current efforts to optimize the detectors for specific applications in safeguards and in materials control and accountability are discussed.