Measurement of natural radioactivity: Calibration and performance of a high-resolution gamma spectrometry facility

Murray et al. (2015) described an international inter-comparison of dose rate measurements undertaken using a homogenised beach ridge sand from Jutland, Denmark. The measured concentrations for ²²⁶Ra, ²³²Th and ⁴⁰K from different laboratories varied considerably, with relative standard deviations of 26% (n=8), 59% (n=23) and 15% (n=23), respectively. In contrast, the relative standard deviations observed internally within our laboratory were 9%, 11% and 7%, respectively (n=20), and in addition our mean values were consistent with the global ⁴⁰K mean, but significantly different from the ²³2Th mean. These problems in both accuracy and precision have led us to examine both the long term performance of our analytical facility, and its calibration. Our approach to the preparation of new absolute ²³⁸U, ²³²Th and ⁴⁰K standards is outlined and tested against international standards. We also report analyses of the Volkegem (De Corte et al., 2007) and Nussi (Preusser and Kasper, 2001) loess samples, for further comparison with other laboratories.