Determining the minimum detectable activity of coincidence HPGe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg" display="inline" id="d1e557"> <mml:mi mathvariant="normal">γ</mml:mi> </mml:math> -ray spectrometers using simulation tools

Coincidence γ -ray spectrometers are promising candidates for future radionuclide monitoring systems, due to their improved minimum detectable activity (MDA) compared to most single-detector systems. To evaluate the performance of future detector designs, a simulation approach to determining MDA using the Geant4 toolkit is proposed in this work. In particular, a phenomenological γ -ray background model was developed and validated against γ -ray coincidence measurements in unshielded and shielded environments. The background model performs well in the unshielded case, where single γ -ray background dominates, but underestimates coincidence spectra in the shielded case. An example of how MDA can be calculated as a function of a detector design parameter is presented to facilitate future detector optimization work.