Evaluation of response functions of 16 inch x 16 inch x 4 inch large-sized N[lc]aI scintillation detector for environmental gamma-ray survey

Abstract

Response functions of the 16' x l6' x 4' -large sized NaI detector, which is mainly used for high sensitive gamma-ray survey in outdoor environment, have been calculated by using EGS4 code. The calculated results are compared with the measured data for standard gamma-ray sources to check their accuracy. Through the precise modeling of the detector structure in the calculation, the agreement between both results has been improved up to around +/- 15 percent relative deviation in Cs-137 source spectrum. Based on this calculation model, the directional response matrix consisting of 24 energy groups x 256 pulse height bins has been prepared to unfold gamma ray spectra from the measured data. The unfolding results seem to be reasonable in a preliminary analysis on natural background gamma-ray spectra.