Monte Carlo model of HPGe detectors used in routine lung counting

An MCNP model of a pair of planar HPGe detectors (designated as: detector 3 and detector 4), that are used for routine lung counting at AECL, was developed. The model was benchmarked against experimental results, where a multi-line (152)Eu source was counted in several different geometrical arrangements. The best agreement for both detectors was achieved when side and back dead layers (of both detectors) were quadrupled, with respect to the ones quoted by their manufacturer (Canberra). In the case of detector 4, the agreement between simulated and measured spectra was within 4%, throughout the whole γ-spectrum, spanning 70-1600 keV. The same was true for detector 3 at the lower end of the γ-spectrum. However, at the high end of the γ-spectrum, the agreement was within 7% and 12% for (152)Eu γ-lines at 778.9 and 1408.01 keV.