Monte Carlo calculation of PEAK efficiencies of Ge(Li) and pure Ge detectors to voluminal sources and comparison with environmental radioactivity measurement

The Monte Carlo code PEAK was developed to calculate the peak efficiency of Ge(Li) and pure Ge detectors to voluminal sources of cylindrical and Marinelli-type shapes. The peak efficiencies calculated by the PEAK code were compared with the results measured by two true-coaxial Ge(Li) detectors with relative efficiencies of 8% and 18%. The calculated peak efficiencies show very good agreement within about 5% with the experimental results both for radioactive agar, activated alumina and manganese dioxide samples in a cylindrical vessel and for a 137Cs aqueous solution in a Marinelli-type vessel. The self-absorption fraction was expressed by one smoothly decreasing curve with the linear attenuation coefficient of a photon in the source medium, independently of its component and the detector size. (orig.)