Methods for spectral interference corrections for direct measurements of ²³⁴U and ²³⁰Th in materials by gamma-ray spectrometry

When the high-resolution gamma-ray spectrometry was used in the analysis of ²³⁴U and ²³⁰Th in samples, there is a much more need to correct for the measured activity results of ²³⁴U and ²³⁰Th mainly due to self-absorption effects and the interfering lines from ²²⁶Ra, ²³⁵U, ²³⁸U and their decay products that often might be present in the samples. Therefore, in the present study, the methods for the spectral interference corrections for the analytical peaks of ²³⁴U and ²³⁰Th are suggested to take into account the contributions of the overlapping gamma rays to these peaks. For the method validation, direct gamma-ray spectrometric measurements were carried out using certified reference materials (CRM) by use of a 76.5 % n-type Ge detector. The activities measured for the CRM samples were corrected for spectral interferences, self-absorption and true coincidence-summing (TCS) effects. The obtained results indicate that ignoring of the contribution of the interference gamma rays to the main analytical peak at 53.2 keV of ²³⁴U leads to a lager systematic error of 87.3-90.4 % for the measured activities of ²³⁴U, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of ²³⁰Th, this leads to a much smaller systematic error of 2.1-2.7 % for the activities of ²³⁰Th. Therefore, the required correction factors for spectral interferences to the analytical peaks of ²³⁴U and ²³⁰Th are not negligible and thus they should also be considered besides necessary self-absorption factors to determine more accurate activities in the samples. On the other hand, it is estimated that although the TCS effects on the main analytical peaks of both ²³⁴U and ²³⁰Th are negligibly small, those TCS correction factors for their interference gamma rays to these peaks should be taken into account when direct measurements are performed in a close-counting geometry condition. Otherwise, the resulted activities can have serious erroneous results for both ²³⁴U and ²³⁰Th while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.