Correction methodology for the spectral interfering γ-rays overlapping to the analytical peaks used in the analysis of 232Th

In the γ-ray spectrometric analysis of the radionuclides, a correction factor is generally required for the spectral interfering γ-rays in determining the net areas of the analytical peaks because some interfering γ-rays often might contribute to the analytical peaks of interest. In present study, a correction methodology for the spectral interfering γ-rays (CSI) is described. In particular, in the analysis of ²³²Th contained in samples, the interfering γ-rays due to ²²⁶Ra, ²³⁵U, ²³⁸U and their decay products often overlap to the peaks of interest from ²³²Th decay products, and vise versa. For the validation of the proposed CSI method, several certified reference materials (CRM) containing U and Th were measured by using a 76.5% efficient n-type Ge detector. The required correction factors were quantified for spectral interference, self-absorption and true coincidence summing (TCS) effects for the relevant γ-rays. The measured results indicate that if one ignores the contributions of the interfering γ-rays to the analytical peaks at 583.2keV of ²⁰⁸Tl and 727.3keV of ²¹²Bi, this leads to a significantly systematic influence on the resulted activities of ²³²Th. The correction factors required for spectral interference and TCS effects are estimated to be ~13.6% and ~15.4% for 583.2keV peak. For the 727.3keV peak, the correction factor is estimated to be ~15% for spectral interference, and ~5% for the TCS effects at the presently used detection geometry. On the other hand, the measured results also indicate that ignoring the contribution of the interfering γ-rays to the areas of the analytical peaks at 860.6keV of ²⁰⁸Tl, 338.3 and 911.2keV of ²²⁸Ac does not lead to any significant systematic influence on the ²³²Th analysis. Because these factors are remained generally less than ~5%, i.e., within overall uncertainty limits. The present study also showed that in view of both the spectral interference and TCS effects, the "cleaner" analytical peaks are seen at 338.3keV (11.25%) and 911.2keV (26.13%) of ²²⁸Ac when high resolution γ-rays spectrometry was used in the ²³²Th activity measurements. Therefore, they can be adopted as the "reference" peaks in the ²³²Th analysis.