Helium Solubility, Mobility, and Implantation Effects in Potassium Bromide

Abstract

The solubility and mobility of He in single-crystal KBr has been determined using three methods: (a) permeation, (b) He release after soaking, and (c) ion implantation. Permeation experiments give values for the activation energies of diffusion and permeation of 0.34-0.39 and 0.63 eV, respectively, and a heat of solution of 0.29 eV. Measurements of gas release from crystals implanted with ${10}^{16}$ ${\mathrm{He}}^{+}$ ions/${\mathrm{cm}}^2$ at 300 keV yield an activation energy for gas release of ∼0.6 eV. The diffusion in the undamaged crystal is interpreted as due to interstitial motion of the He atom. A very low solubility, on the order of ${10}^{14}$ He atoms ${\mathrm{cm}}^{-3\mathrm{}}$ ${\mathrm{atm}}^{-1\mathrm{}}$, was determined in the range of 100-200 °C, which is believed to be the first measured solubility of a rare gas in an alkali halide. Finally, it is shown that diffusion measurements such as those reported here for an undamaged crystal are insensitive to traps if typical concentrations and reasonable trap depths are used.