Xe isotopic fractionation in a cathodeless glow discharge

Abstract

We report results on the isotopic composition of Xe processed in cathodeless glow discharges in rarefied air at pressures of 20–40 microns Hg, in the presence of activated charcoal and in empty pyrex containers. Residual gas phase Xe and trapped Xe were found to be fractionated. The trapped Xe compositions were fractionated up to 1% per amu. We present a model for the fractionation process in which Xe ions are simultaneously implanted and sputtered from substrate material, with a mass dependence favoring retention of the heavy isotopes in the substrate. Comparison of the model predicted fractionations with the experimental data indicates an m1 mass dependence for the overall fractionation process. The data also seem to favor an m1 dependence for the implantation and no mass dependence for the sputtering process, although this conclusion is less secure. The results show that plasma synthesis of carbonaceous material is unnecessary for producing Xe fractionations, and that the fractionations observed in previous synthesis experiments are likely due to implantation of ions into the synthesized material.