Calibration of the 4π γ-ray spectrometer using a new numerical simulation approach

The 4π γ-counting system is well suited for analysis of small environmental samples of low activity because it combines advantages of the low background and the high detection efficiency due to the 4π solid angle. A new numerical simulation approach is proposed for the HPGe well-type detector geometry to calculate the full-energy peak and the total efficiencies, as well as to correct for the coincidence summing effect. This method depends on a calculation of the solid angle subtended by the source to the detector at the point of entrance, (Abbas, 2006a). The calculations are carried out for non-axial point and cylindrical sources inside the detector cavity. Attenuation of photons within the source itself (self-attenuation), the source container, the detector's end-cap and the detector's dead layer materials is also taken into account. In the Belgium Nuclear Research Center, low-activity aqueous solutions of 60Co and 88Y in small vials are routinely used to calibrate a γ-ray p-type well HPGe detector in the 60-1836 keV energy range. Efficiency values measured under such conditions are in good agreement with those obtained by the numerical simulation.