Detector optimization for hand-held CsI(Tl)/HgI2 gamma-ray scintillation spectrometer applications

Gamma-ray spectrometers using mercuric iodide (HgI₂) photodetectors (PDs) coupled with CsI(Tl) scintillators have shown excellent energy resolutions and high detection efficiency at room temperature. Additionally HgI₂ 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 hydrogel 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. larger 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