Resurrected from the dead: Full characterization of an old HPGe detector using γ-ray and CT tomographies coupled to standard calibration techniques and simulations

Abstract

A decommissioned co-axial HPGe detector has been recently acquired and returned to operational mode in an effort to build an environmental radiation spectrometer at the University of Athens. The new counting station, GEROS (Germanium for Environmental RadiOactivity Studies), was fully characterized prior to operation to obtain detailed information on its linear response, efficiency and energy resolution. In addition to using point-like calibration sources (60Co,137Cs,152Eu and 226Ra), several bulk sample geometries were calibrated by means of an IAEA standard, focusing on soils, sediments and solid materials. In lieu of deteailed technical specifications, the crystal integrity, especially in regards to the dead layer known to build up over the years was studied by means of γ-ray tomography. The 3D geometry of the crystal was fully reconstructed considering the absorption coefficients, and the dead layer thickness was estimated. The overall crystal alignment inside the case was also checked. The results were verified by placing GEROS inside a medical CT scanner and irradiating it to obtain detailed longitudinal and transverse sections. The results were combined to provide input data for subsequent MCNP5 simulations. Good overall agreement between simulations and measurements was achieved. Despite some expected loss of resolution, the detector was found to perform substantially well.