Validation of efficiency calibration of HPGe well-type detector using a 85Sr standard solution

The application of near 4 pi counting geometry for determining low-level gamma-emitters improves detection limits considerably. At the same time, true coincidence effect is pronounced in a well-type counter, and requires correction for loss of coincidence. Therefore, only single-photon emitting radionuclides can be used for efficiency calibration. An efficiency calibration was performed for a particular HPGe well-type detector using reference standard solutions with 57Co, 137Cs, 54Mn, 65Zn and 40K. This set of radionuclides allowed to construct a calibration curve that provided overall uncertainty of 6% in activity measurements in the energy region of 122-1461 keV. However, the first half of this region (122-662 keV) lacked suitable calibration points; it was therefore expected that any additional point could enhance calibration. 85Sr reference standard solution was applied for this task where available. The counting efficiency was investigated taking into account the filling height of the measuring container. Detector response at 514 keV was included in a new efficiency curve construction, which made it possible to improve the precision of previous calibration.(author)