Subtraction of natural radiation contribution from gamma-ray spectra measured by HPGe detector

Highlights: • New system with HPGe detector was used for measurement of radioactivity on filters. • Monte Carlo method was used for calculation of radionuclides detector spectra. • Natural radionuclides spectra were subtracted from measured spectrum. • The method was tested experimentally with a Cs-137 source. - Abstract: A method is described for the subtraction of Monte Carlo simulated detector spectra of the contribution of natural radiation to measured detector spectra aiming to decrease the decision threshold for the detection of artificial radionuclides. HPGe detector spectra were simulated for selected naturally occurring radionuclides deposited onto a filter used for aerosol collection in a newly developed airborne radioactivity monitoring system. Stepwise, the simulated spectra were fitted to the actually acquired gamma-ray spectrum and the decision threshold was determined. Contribution of cosmic rays background was also estimated.