Monte Carlo simulation of the beta-ray induced X-ray spectra of tritium at various depths in solids

Non-destructive methods to measure tritium in solids are required for material studies and managements of tritium-contaminated material in the field of fusion research. The beta particle generated by tritium decay cannot usually escape from solids. Namely, the beta particle of tritium decay is difficult to detect in solids. Conversely, the X-rays induced by beta particles in solids escape from the solid, and they can then be detected outside the solid. This is the basis of beta-ray induced X-ray (BIX) spectrometry (BIXS) of tritium. BIXS has potential for quantitative tritium analysis, but it is qualitative rather than quantitative for the solid phase. Because the number and energy of detected X-ray photons depend on the distribution of tritium in the solid, the shape of the BIX spectrum reflects the tritium distribution in the solid. For a quantitative tritium analysis, the tritium distribution in the solid would be evaluated by the shape of the BIX spectrum. In this study, Monte Carlo simulations were employed to determine the change in the BIX spectrum with the tritium depth. The relative intensity of the characteristic X-ray had the information about the tritium distribution and constituent elements of both a solid and an atmosphere. However, the change in the BIX spectrum with the tritium depth depended on the solid material. To consider the BIX spectrum of an unknown solid sample containing tritium, Monte Carlo simulation of the BIX spectrum is indispensable.