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When the high-resolution gamma-ray spectrometry was used in the analysis of Th mainly due to self-absorption effects and the interfering lines from 226 Ra, 235U, 238 U 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 234 U and 230 Th 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 234 U leads to a lager systematic error of 87.3-90.4 % for the measured activities of 234 U, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of 230 Th, this leads to a much smaller systematic error of 2.1-2.7 % for the activities of 230 Th. Therefore, the required correction factors for spectral interferences to the analytical peaks of 234 U and 230 Th 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 234 U and 230 Th 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 234 U and 230 Th while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.

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