Dependence of the virtual point-detector location on HPGe detector dimensions and source energy in 80-1400 keV range

Variations of VPD position inside HPGe detector as function of source photon energy and dimension of the detector is investigated. Monte Carlo code MCNP4C is employed to compute the detector efficiency for varying source-detector distance. The efficiency is measured in practice. The experimental results are obtained and compared with Monte Carlo output for energy range 80-1400 keV and source-detector distances 1-10 cm. it is shown that the depth of VPD increases with photon energy up to 600 keV and remains with little significant changes at higher energies. With increasing the detector radius the VPD is located deeper into the detector. The distance between VPD and entrance window is calculated to vary from 2 cm to 4 cm for detector radius between 2.5 cm to 4.7 cm.