Comprehensive determination of elements ranging from uranium to americium by hybrid measurement of fluorescent and spontaneously emitted characteristic X-rays

Natural uranium isotopes have extremely long half-lives; therefore, analytical methods based on the number of atoms, such as X-ray fluorescence (XRF) analysis, are suitable for uranium detection. However, XRF measurements cannot be used to detect the major isotopes of americium when present in amounts barely detectable using radiation measurements, owing to their relatively short half-lives. Because of α-decay-induced internal conversion, where orbital electrons are emitted instead of γ-rays, these nuclides emit characteristic X-rays. Measuring such spontaneously emitted characteristic X-rays is suitable for nuclides with short half-lives because the intensity of such X-rays correlates with the radioactivity of the nuclides. In this study, we developed a comprehensive analysis for the detection of trace amounts of uranium, neptunium, plutonium, and americium isotopes by a hybrid measurement approach involving fluorescence and spontaneously emitted characteristic X-rays. Furthermore, we evaluated the suitability of the methods for each element. XRF analysis was suitable for quantifying uranium and neptunium, while the measurement of spontaneously emitted characteristic X-rays was suitable for detecting americium. However, the results from both methods were comparable for plutonium. Additionally, the spontaneously emitted characteristic X-rays did not affect the XRF analysis for trace amounts of actinides. We believe that this method can be applied to a wider range of actinide isotopes in the future.