Call of duty: recommissioning an old HPGe detector

Abstract

A decommissioned p-type, co-axial HPGe detector has been recently brought back to operational mode in an effort to build a γ-ray spectroscopy station at the National and Kapodistrian University of Athens dedicated for environmental radioactivity studies. The detector was fully characterized prior to and during its operation to obtain detailed information on its linear response, efficiency and energy resolution. The geometrical features of the HPGe crystal were studied with a combination of X-ray CT, γ-ray tomography and detailed simulations with both MCNP5 and Geant4. A 3D reconstruction of the crystal was attempted using the recorded data to examine its overall placement and alignment inside the enclosure. Due to the prolonged inactivity, the crystal integrity and the dead layer expected to develop over the years were additionally studied. The results show that after about three decades of inactivity, the active volume of the crystal has been reduced significantly, an effect having an impact on its quality features (resolution, efficiency). Overall, the detector was found to perform substantially well.