Improving the assessment of activity in samples with non-uniform distribution using the sum peak count rate

In this work a method for the evaluation of the activity when a point source containing 60Co is located in an unknown position within a sample is developed. The method can be applied if the count rate in the 2505 keV sum peak has an acceptable uncertainty. It is based on the correlation between the apparent efficiency for the 1173 keV peak and the ratio of the count rate in the sum peak of 2505 keV and in the 1332 keV peak. The correlation was observed in the measurements of a 60Co point source located in various positions in a soil sample. The measurements were done with a 47% efficiency n-type HPGe detector. The correlation is also observed in the measurements and simulations done with a Compton-suppressed spectrometer having a 100% n-type HPGe detector. The results obtained with the proposed method are less affected by the uncertainty of the position of the point source than the results obtained using the standard methods of activity evaluation.