Design and Setup of a New HPGe Detector Based Body Counter Capable of Detecting Also Low Energy Photon Emitters

Germanium detectors allow for an accurate detection of complex contamination cases involving multiple nuclides, but they are available in smaller sizes than scintillators and therefore require careful optimisation of the counting configuration. This work describes the complete redesign of the partialbody and whole-body counter installed at IVM (KIT, Karlsruhe) and the first results of its application. To speed up the design process, each detector was modelled using MCNPX and the validated models used for all the subsequent steps. The definition of the partial-body counting configurations was performed exclusively with the help of simulations of voxel models of the human body: the photon fluxes around it were tracked and the detectors placed in the optimal positions. The configurations obtained were used as guideline to define the supporting mechanics. The development of a whole-body counting (WBC) configuration was also performed using MC simulations and the photon flux, but in this case different results for different organs, phantoms and energies were aggregated to calculate average values and standard deviation. These two new quantities were used to optimise the setup. Once the system and the mechanics were ready, different tests were performed. First, a reference phantom was used to quantify the improvement in the detection limit compared to the previous system. Later, two subjects potentially contaminated with Pb were measured on the skull. This test aimed to check the lowest-energies capabilities of the system (46 keV). A last test involved the measurement of subjects returning from Japan after the Fukushima accident, with mixed results.