RNRA and neutron threshold analyses of thick lithium coatings deposited by sputter evaporation

Abstract

Li coatings on various substrates have numerous applications: Boron neutron capture therapy, super conducting tokamak, etc. Unfortunately the main difficulty using Li is its reactivity in air and diffusion into metals. It is the only metal that reacts with nitrogen at room temperature and it tarnishes and oxidizes rapidly in air. In this work, we investigate how to profile thick Li layers (50 μm) deposited on SiO2 substrates by a method based on plasma sputtering, involving both DC sputtering and evaporation simultaneously. A thick Li layer (≈10 μm) was covered with a thin stainless steel layer to prevent oxidation during transfer of the sample from the sputtering chamber and the accelerator. Li coatings were investigated by RNRA and neutron threshold reaction to obtain interdiffusion profiles of the different components and their concentration. The depth profile using the 7Li(p,γ)8Be* resonance nuclear reaction occurring at 440 keV allows us to obtain Li concentration versus depth up to 50 μm. Preliminary results indicate that homogeneous Li layers can be obtained and protected against air, even though it diffuses into the encapsulated layers. © 2008.