Calibration of an in-situ BEGe detector using semi-empirical and Monte Carlo techniques

In the case of a nuclear or radiological accident a rapid estimation of the qualitative and quantitative characteristics of the potential radioactive pollution is needed. For aerial releases the radioactive pollutants are finally deposited on the ground forming a surface source. In this case, in-situ γ-ray spectrometry is a powerful tool for the determination of ground pollution. In this work, the procedure followed at the Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) for the calibration of an in-situ Broad Energy Germanium (BEGe) detector, for the determination of gamma-emitting radionuclides deposited on the ground surface, is presented. BEGe detectors due to their technical characteristics are suitable for the analysis of photons in a wide energy region. Two different techniques were applied for the full-energy peak efficiency calibration of the BEGe detector in the energy region 601600 keV:

• a semi-empirical method based on the determination of the peak efficiency for a surface source geometry, from the experimentally obtained efficiency for a point source geometry
• a numerical method which is based on Monte Carlo simulation. For this purpose the PENELOPE computer code was employed. For the determination of the geometrical characteristics of the detector a key parameter for the simulation accuracy an iterative procedure involving a series of experiments and simulations was applied.

Full-energy peak efficiencies determined using the two methods agree within statistical uncertainties.