Determination of a standard efficiency using the ISOCS uncertainty estimator for calculating the activity concentration of 226Ra, 232Th, and 40K in concrete

• The standard efficiency makes it possible to determine the concentration of natural radionuclides in concrete specimens. • The activity concentrations obtained in the final material were equivalent to those obtained by grinding these materials. • The IUE allows us to obtain an average efficiency from the variation in the dimensions, density, and composition of the concrete. The Activity Concentration Index (ACI) requires knowledge of the activity concentrations of 226 Ra, 232 Th ( 212 Pb), and 40 K, typically determined through gamma spectrometry. The inherent heterogeneity of concrete makes the determination of gamma counting efficiency a complex problem. For this reason, this study employed the ISOCS Uncertainty Estimator (IUE), which allows for probabilistic calculations based on variations in parameters affecting counting efficiency, such as dimensions, density, and composition. The IUE enabled the estimation of a representative efficiency for a standard concrete configuration applicable to concrete specimens and samples from existing structures. The results obtained with the proposed efficiency for natural radionuclides of the uranium and thorium series, along with 40 K, compared to the classical material grinding method, showed no significant differences in the mean and variance. The maximum differences observed when applying regression analysis were less than 16 %, thus validating the representative efficiency obtained with the IUE.