Radioanalytical determination of actinoids in refractory matrices by alkali fusion

In this work a method used conventionally for ICP-MS measurements have been modified and readapted for the determination of actinides (U and Th isotopes) in refractory samples by alpha-spectrometry. The method is based in a total dissolution of the sample by alkali fusion. In the first stages of our studies, we try to digest refractory samples by leaching with aqua regia followed by the application of a liquid–liquid solvent extraction process for the sequential isolation of the uranium and thorium isotopes from the dissolved fraction. These actinides were finally electroplated in stainless steel discs and measured in an alpha-spectrometer using PIPS detectors. On the other hand, gamma measurements were carried out in aliquots of the same samples in order to check the results produced by alpha spectrometry. Clear disagreements were found between the results obtained by both techniques. This problem was solved by the application of an alkali fusion technique where a total dissolution of the sample is performed. It was found in addition that the alkali fusion is easily applicable, less time-consuming, needs less reagents than leaching and it does not require sophisticated apparatus to be executed. In this paper the whole procedure for U and Th determination in refractory samples by alpha-spectrometry with alkali fusion is presented and validated.