Validation of the quantification of natural radionuclides in raw materials and by-products using gamma-ray spectrometry

The validation of a method for the indirect quantification for 238U, 226Ra, and 232Th activity and the direct quantification for 40K activity using gamma-ray spectrometry was performed in view of consistency, reliability, and accuracy of the results. The gas tightness of Al containers used to confine the radon gas was verified from the establishment of the secular equilibrium between 226Ra and its indicator. To evaluate validation parameters such as linearity, range, and accuracy, it was important to verify the equilibrium state of the reference materials (RM) for U and Th, because the ingrowth of progenies in the uranium decay series can affect the quantification of 226Ra activity even if based on a certified reference material (CRM), while the ingrowth of 228Ra from the thorium decay series should be secured in order to use 228Ac as an indicator of 232Th. In addition, the ruggedness of the method regarding different materials was checked using two kinds of CRM, namely bauxite as an example of a raw material and coal fly ash as a by-product.