Gamma-Ray Detection Efficiency and Image Resolution in Sodium Iodide

Abstract

Photoelectric, Compton, and photopeak efficiencies have been calculated at several gamma-ray energies for large flat sodium iodide crystals in which the thickness ranges from ⅛−2 in. Also, the loss of position resolution by gamma-ray scattering within the scintillator is calculated, since this is of interest in the design of gamma-ray imaging devices like the scintillation camera. An examination of the data shows the advantage of using low energy gamma rays for imaging whenever possible. They are efficiently detected by solid sodium iodide scintillators ½ in. thick, and there is little loss of resolution due to scattering of gamma rays in the scintillator. In the higher energy range, a choice must be made between a thin scintillator with its relatively good position resolution and low detection efficiency, or a thick crystal with higher detection efficiency and less satisfactory resolution.