Efficiency calibration of NaI (Tl) detector for disc source using point source experimental technique and Monte Carlo simulations

The detection efficiency of a gamma ray detector should be calibrated prior to the measurement of activity in samples. The aim of this research is to develop a simple experimental technique to calibrate the efficiency of detectors for geometrical sources by replicating their responses from virtually equivalent sources (VES) constructed from a collection of Standard Point Source (SPS) measurements. Experiments were performed to replicate the response of a disk source of 5.2 cm radius by equivalent disk sources (EDS) reconstructed from a collection of 19, 91 and 169 SPS measurements to optimize the number of measurements, response of detector for radially symmetric SPS locations was verified through Absolute Peak Efficiency (APE) calculations. APE was calculated experimentally for the actual disk source and EDS as well as using EGS5 simulations. The difference between experimentally measured and simulated APE for 5.2 cm EDS was observed to be about 7.8 %, 5.2 % and 5.4 % for 137Cs and about -1.3 %, 1.3 % and 2.7 % for 22Na for the EDS constructed from 19, 91- and 169 SPS measurements respectively