Abstract
Elemental and isotopic mass fractionation in both binary and multicomponent media are investigated within the framework of the familiar collision-cascade model for sputtering. Some of the most salient features of the phenomenon are explicable on this basis. It is found that the partitioning of beam-deposited energy among the various target components can account for differentiations in the secondary recoil fluxes only on the order of one part per thousand, indicating the importance of the surface potentials when large enrichment effects occur. A mechanism governing the translation of internal recoil fluxes into external sputtered fluxes is proposed in order to account for isotopic fractionation, for which the surface binding effects are assumed to be negligible. The predicted initial fractionations are δf(40Ca : 44Ca) =33 parts per thousand in the calcium-containing mineral plagioclase and δf(40Ca : 44Ca) =24 parts per thousand in CaF2, in reasonable agreement with recent data on isotopic fractionation.
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