Abstract
A large number of environmental samples are routinely measured world-wide using gamma-ray spectrometry some of its assets being easy sample preparation and comprehensive data for many radionu-clides in one analysis. Although other techniques can be considered more suitable for analysing 238U in environmental samples, it is also routinely done by gamma-ray spectrometry. One mainly uses γ-ray emissions following the decay of the first daughter, 234Th, for determining the 238U activity. However, the low-energy gamma-rays at 63 keV and 92.5 keV are very difficult to quantify in a robust way due to high attenuation and interferences. This paper quantifies parameters affecting the possibility of making robust quantification of 238U via 234Th using gamma-ray spectrometry. It addresses the use of correct decay data, suitable detectors, optimised sample size, enhanced spectral amplification, correction for peak interferences and control of background.
Highlights
Gamma-ray spectrometry using HPGe-detectors is a widely used technique in laboratories monitoring environmental radioactivity
A large number of environmental samples are routinely measured world-wide using gamma-ray spectrometry, some of its assets being easy sample preparation and comprehensive data for many radionuclides in one analysis
Other techniques can be considered more suitable for analysing 238U in environmental samples, it is routinely done by gamma-ray spectrometry
Summary
Gamma-ray spectrometry using HPGe-detectors is a widely used technique in laboratories monitoring environmental radioactivity. The detection limits of radionuclides emitting gamma-rays of low energy (< 100 keV) suffer from being in a matrix with other radionuclides emitting gamma-rays of higher energy due to interferences with X-rays and scattered gamma-rays. This is generally the case when quantifying 238U in an environmental sample like soil. Uranium-238 is a primordial radionuclide that is important to monitor It decays by alpha-decay to 234Th, which generates low-energy gamma-rays with very low emission probability. The gamma-rays at 767 and 1001 keV are robust for quantification but due to their low emission probabilities (0.317% and 0.842%, respectively) they are often swamped by the background from other radionuclides in the environmental sample itself. In this paper we will refer to the two doublet peaks as if they were singlet peaks at 63 keV and 92.5 keV
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