HPGe well detector calibration procedure by MCNP5 Monte Carlo computer code

The determination of response curves for HPGe detector demand a large number of gamma sources in order to account for the energy range of interest for a given counting geometry. HPGe well detectors present an additional difficulty, related to the large sum effect for sources placed inside the well, either limiting the useful sources or large analytical corrections, which might imply in large uncertainties. The Monte Carlo method can be used to determine a detector’s response curves which are difficult to obtain experimentally. The MCNP5 computer code provides means to simulate gamma ray detectors and has been used for this work for the 50–2000 keV energy range. The detector’s sensitive volume was determined by comparison of simulated and measured spectra due to two point sources, 241Am and 137Cs. The thickness of the dead layer + transition layer was determined for all crystal’s surfaces, and the response curves for two volumetric sources geometries, one placed on top of the detector and a smaller one placed inside the well, were then obtained by simulation and compared with the experimental results, in order to verify and validate the detector’s simulation. Both simulated and experimental response curves were in very good agreement.

► We verify the validation of MCNP5 computer code in determining efficiency curves.
► We use an HPGe well detector with 40% of relative efficiency.
► The results show that MCNP5 is a important tool for the detector’s response curves determination.