Simultaneous determination of Ra-226 and U-238 in soil and environmental materials by gamma-spectrometry in the absence of radium progeny equilibrium

The determination of Ra-226 and U-238 in environmental samples by gamma-spectrometry is most often carried out by hermetic sealing of the sample in a suitable container, waiting until secular equilibrium that has been established in the U-238 decay chain below Ra-226 and counting of the high intensity emissions of Ph-214 and Bi-214. The 186 keV multiplet can then be corrected to provide a measure of U-235 and hence, U-238. The work presented in this paper involves a critical examination of the analysis of U-238 and Ra-226 in environmental materials without secular equilibrium established between Pb-214, Bi-214 and their progenitor. Results indicate that the correction of the 186 keV doublet via Th-234 determination is possible, even for low-level samples but careful consideration of both experimental conditions and the composition of the sample matrix is required.