Evaluation the nonlinear response function of a 3×3 in NaI scintillation detector for PGNAA applications

Response functions of the 3×3 in NaI detector, which is mainly used in PGNAA applications, have been calculated by using MCNP-4C code. Calculated results are compared with measured data by using standard γ-ray sources and prompt γ-rays from pure element samples to check their accuracy. Prompt γ-rays from pure element samples were used for this determination in the range from 1.942 to 10.829 MeV by use of 241Am–Be neutron source and γ-rays from radioisotope sources were used in the range from 0.081 to 4.438 MeV. Through the precise modeling of the detector structure, the agreement between both results has been improved. A surprising result is that in the PGNAA method the agreement between the MCNP simulation and experiment will be better by using a suitable neutron shield for NaI detector in order to prevent the activation of NaI (Tl) and a proper γ-shield to attenuate the high-rate 4.438 MeV γ-ray, 241Am–Be γ-ray component.