Experimental and Monte Carlo determination of HPGe efficiency for environmental samples

HPGe detectors are commonly used in the laboratories to detect gamma-rays due to its high resolution and efficiency which is a good characteristic to distinguish low energy gamma radiation. In the present study a HPGe detector called Ge5 of LARA Laboratori d’anàlisi de radiactivitat ambiental (INTE-UPC) must be studied because it is intended to be used again to get the activities of several samples. The first step is to get the efficiency calibration for environmental samples which are small and large filters. Efficiency calibration can be obtained experimentally but the efficiency curves would not be reliable for a continuum energy range. Moreover, HPGe detector are limited because some of the radionuclides such as 60Co releases more than one gamma-ray at the same time and distorts the actual efficiency. Therefore, it is needed to get correction factors. Monte Carlo methods are used to get efficiency calibration so that an accurate efficiency curve can be obtained for a wide energy range. Moreover, the correction factors can be computed. PENELOPE/PenEasy is the program used to get the efficiency calibration for small and large filters and correct the efficiency of 60Co due to the true coincidence summing effect. This program will also allow to define the geometry of the Ge5 detector since the layout is unknown. In order to determine the geometry of the detector Ge5 a previous simulation is done with old environmental samples. After characterizing the geometry of the detector, a current experiment with a large filter is simulated to get a new efficiency calibration which is the main goal of the project.