SODIUM-IODIDE DETECTOR RESPONSE FUNCTIONS USING SIMPLIFIED MONTE-CARLO SIMULATION AND PRINCIPAL COMPONENTS

A new approach has been developed, validated and demonstrated for gene rating detector response functions for gamma-rays incident on NaI dete ctors. The approach is demonstrated for gamma-rays with energies from 0.5 to 10.5 MeV incident on 3'' x 3'' and 6'' x 6'' cylindrical detect ors. The gamma-ray source used here is a point isotropic source locate d 10 cm from the detector face on the detector axis. However, the appr oach is very general and could be used for any other geometry desired and any detector type, with appropriate Monte Carlo simulation. A spec ific purpose Monte Carlo simulation code called DRFNCS has been design ed for this purpose and was benchmarked against the general purpose IT S electron/photon codes developed by Sandia National Laboratories. The DRFNCS code is orders of magnitude faster than the ITS general purpos e code and allows one to practically simulate the large number of spec tra that are required for this purpose. Then the method of principal c omponents is applied to the Monte Carlo data. This reduces the amount of data required and allows detector response functions to be generate d efficiently and accurately for any gamma-ray energy within the speci fied energy range.