Simulated performance of the Gamma Tracker CdZnTe handheld radioisotope identifier

Abstract-The GammaTracker handheld radioisotope identifier currently under development at the Pacific Northwest National Laboratory uses a pixellated CdZnTe spectrometer array to measure the energy and incoming direction of gamma rays from 50 keV to 3 MeV. This instrument, which incorporates the Polaris technology developed at the University of Michigan, houses two 3times3 arrays of 2.25-cm³ CdZnTe detectors. In this work, we present Geant4 simulation results of gamma-ray detection, identification, and directionality performance of the GammaTracker instrument. Estimated minimum detectable activities (MDAs) are determined to be only 20-30% higher than the MDAs predicted for a comparable-efficiency HPGe system over a reasonable energy range. The simulated imaging resolution is determined to be ~20deg FWHM, and the imaging efficiency is evaluated as a function of gamma-ray energy.