α-Spectroscopy as a tool to measure very small diffusion coefficients

Abstract

In the past eight years, α-spectroscopy has been increasingly used to study diffusion profiles, especially in nuclear materials, employing the method of “α-energy degradation”. The mathematics to extend the applicability of this method down to very small diffusion distances corresponding to extremely small diffusion coefficients of the order of 10−18 cm2/s have been developed. It is shown that three quantities can be used to deduce diffusion coefficients: 1.1) the extension of the spectra towards lower energies,2.2) a shift in the position of the peak towards lower energies, and3.3) the remaining counting rate at the original energy, E0. The relations between these quantities and the diffusion coefficient are given graphically for different resolutions of the α-spectrometer. Allowance is made for the limited resolution and for more than one α-energy in the decay spectrum of the tracer nuclide. Finally, corrections are given for the case that the thickness of the tracer layer is not negligible as compared to the diffusion distance.