Sourceless efficiency calibration of well-type high purity germanium detector for volume source sample

Efficiency calibration of high purity germanium detector is accurately completed, which is related with accuracy of quantitative analysis for radioactive isotope. The physical model of a well-type high purity germanium detector is constructed by Monte Carlo software MCNP and efficiencies of this detector are determined by sourceless efficiency calibration. For samples with densities of 0.4 gcm-3 and 1.2 gcm-3, efficiencies of gamma rays are simulated by MCNP. When gamma rays energy is larger than 0.10MeV, detection efficiency is mainly related with samples density and gamma ray energy. For samples of soil (density from 0.1 gcm-3 to 1.6 gcm-3 ), aqueous solution (density is 1.0 gcm-3) and oil solution (density is 0.92 gcm-3), combined with the function models, the functions and parameters are determined. Combined with four standard sources, simulations of efficiency are verified, whose efficiencies are in agreement with the experimental values and errors of them are all lower than 3%. It is proved that MCNP code can be used to calculate efficiency of gamma ray for well-type high-purity germanium detector.