Influence of tritium distribution in aluminum and iron for shape of the beta-ray induced X-ray spectrum

Beta-ray induced X-ray spectrometry (BIXS) is commonly used for qualitative measurement of tritium in solids. We considered that BIXS could also be used quantitatively to determine the depth of tritium in solids. To determine the change in the shape of the BIX spectrum with tritium depth, spectra in aluminum and iron were calculated using the Monte Carlo simulation code (Galet-BIXS). The spectral shape was determined by the relative fractions of the characteristic X-ray components and bremsstrahlung. It was changed with the tritium depth, even when the number of tritium decay events was held constant in the simulations. Specifically, the spectral shape gave information about the tritium depth. However, the accuracy of the estimated tritium depth depended not only on the elements that interact with the beta particles but also on the tritium depth. In some cases, the tritium depth could not be evaluated from the BIX spectra. For example, the spectral shape for aluminum in helium was kept up to 10 mu m deep of the tritium depth. When the atmosphere was replaced from helium to argon, the spectral shape was changed with the tritium depth up to 10 mu m. Nevertheless, our method allows quantitative analysis of tritium in solids based on the BIX spectrum in most cases. We believe that the Monte Carlo simulation of the BIX spectrum is crucial to the further development to determine the tritium depth in solids.