Modeling of a HPGe well detector using PENELOPE for the calculation of full energy peak efficiencies for environmental samples

When determining the activity concentration of radionuclides using gamma-ray spectrometry the Full Energy Peak Efficiency (FEPE) for the energies of interest must be known. Determination of the FEPE can be made by means of either experimental calibration or theoretical-mathematical methods, such as Monte Carlo simulations. Given the difficulties related to experimental calibration and improvements in the capabilities of modern computers, Monte Carlo simulation is an increasingly widely used alternative, but requires an accurate model of the detector. The purpose of this work is to generate and validate a computational model, based on Monte Carlo simulation, of an HPGe well detector that permits the performance of FEPE calculations with appropriate precision and accuracy for the measurement of environmental samples. To achieve this, an optimization methodology is applied to the model that minimizes the differences between a set of computational FEPEs and a set of experimental FEPEs used as a benchmark. The resulting optimized model is used to calculate computational FEPEs for 25 different samples with different reference materials and sample heights, which are measured by means of the well detector modeled here. To validate the optimized model, the abovementioned computational FEPEs are used during the calibration of the corresponding spectra, to enable the subsequent comparison of the results of the analyses with the expected values. The measured activities differ from the reference values by less than 10% in most cases and are compatible with these considering the uncertainties involved, thus confirming the validity of the model.