Monte Carlo based geometrical model for efficiency calculation of an n-type HPGe detector

A procedure to optimize the geometrical model of an n-type detector is described. Sixteen lines from seven point sources (241Am, 133Ba, 22Na, 60Co, 57Co, 137Cs and 152Eu) placed at three different source-to-detector distances (10, 20 and 30cm) were used to calibrate a low-background gamma spectrometer between 26 and 1408keV. Direct Monte Carlo techniques using the MCNPX 2.6 and GEANT 4 9.2 codes, and a semi-empirical procedure were performed to obtain theoretical efficiency curves. Since discrepancies were found between experimental and calculated data using the manufacturer parameters of the detector, a detail study of the crystal dimensions and the geometrical configuration is carried out. The relative deviation with experimental data decreases from a mean value of 18–4%, after the parameters were optimized.