Semi-analytical response function for ML-EM deconvolution of NaI detector energy spectra

The response functions of two very different geometry NaI scintillation detectors were derived from a combination of Monte Carlo modeling and semi-analytical extension throughout a wide energy range. The two geometries considered were the 3" right circular cylinder NaI detector, that is the de facto standard for declaring sensitivity for gamma-ray spectrometers, and a 50×40×1 cm³ NaI plate, that is typical of nuclear medicine gamma cameras. The response functions, encompassing a range of 50-2500 keV, were developed both to compare the performance of these two detector geometries and to provide the basis for implementing a maximum likelihood-expectation maximization (ML-EM) deconvolution to improve spectroscopic analysis. The goal of this development is to establish the desirability for utilizing nuclear medicine gamma cameras as high sensitivity gamma-ray spectrometers in the event of a radiological emergency.