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

Abstract

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 226 Ra, 232 Th and 40 K 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 40 K mean, but significantly different from the 232 Th 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 238 U, 232 Th and 40 K 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. • γ spectrometry doserates stable over 13 years. • U, Th, K minimum detection limits 0.04, 0.03, 06 B kg −1 , respectively. • New U, K calibration accurate to <2%. • Unable to confirm accuracy of new Th calibration.