Spectral interference corrections for the measurement of 238U in materials rich in thorium by a high resolution γ-ray spectrometry

Abstract

In this study, the spectral interferences are investigated for the analytical peaks at 63.3 keV of 234Th and 1001.0 keV of 234mPa, which are often used in the measurement of 238U activity by the γ-ray spectrometry. The correction methods are suggested to estimate the net peak areas of the γ-rays overlapping the analytical peaks, due to the contribution of 232Th that may not be negligible in materials rich in natural thorium. The activity results for the certified reference materials (CRMs) containing U and Th were measured with a well type Ge detector. The self-absorption and true coincidence-summing (TCS) effects were also taken into account in the measurements. It is found that ignoring the contributions of the interference γ-rays of 232Th and 235U to the mixed peak at 63.3 keV of 234Th ( 238U) leads to the remarkably large systematic influence of 0.8–122% in the measured 238U activity, but in case of ignoring the contribution of 232Th via the interference γ-ray at 1000.7 keV of 228Ac to the mixed peak at 1001 keV of 234mPa ( 238U) results in relatively smaller systematic influence of 0.05–3%, depending on thorium contents in the samples. The present results showed that the necessary correction for the spectral interferences besides self-absorption and TCS effects is also very important to obtain more accurate 238U activity results. Additionally, if one ignores the contribution of 232Th to both 238U and 40K activities in materials, the maximum systematic influence on the effective radiation dose is estimated to be ~6% and ~1% via the analytical peaks at 63.3 and 1001 keV for measurement of the 238U activity, respectively.