Virtual point detector for HPGe detectors for 26.6-1332 keV photon energies by experiment and Monte Carlo simulation

Variation of virtual point detector (VPD) position inside HPGe detector as a function of source photon energy for the energy range from 26.6 to 1,332 keV was investigated. Although VPD concept was well established for HPGe detectors from 59.5 to 10 MeV, a new attempt was made to obtain VPD positions for photon energies below 59.5 keV. It was found that VPD position shows different functional behavior for the energy ranges 26.6-59.5 keV and 59.5-1,332 keV. The VPD position decreases with increasing energy for 26.6, 31.7, 36.4, and 37.3 keV and increases with the energy until it reaches a plateau. The functional behavior of VPD position for the energy range 26.6-59.5 keV was attributed to the dead layer thickness of the Ge crystal. Monte Carlo simulations were performed to investigate the behavior of VPD position with various dead layer thickness ranging from 100 to 800 μm. It was seen that VPD position increases with increasing energy for 31.7, 59.5, and 80.1 keV more significant at relatively lower energies, but constant for the energies 661-1,332 keV.