Direct collection of some metal ions in an electromagnetic isotope separator and related surface effects

Abstract

The direct collection of Fe, Co, Ni, Cu, Zn, and Sn ions has been investigated in the energy range from about 10 eV to 110 keV in an electromagnetic isotope separator. At low energies the ions build up a layer on the surface of the graphite block used as a backing, while at high energies only a certain saturation value can be collected. For these ions the highest energies at which the building-up of a layer was observed were 1.5 keV, 1.0 keV, 0.8 keV, 0.3 keV, 0.3 keV, and 0.45 keV, respectively. In the building-up region the efficiency of the collection process and the sticking probability of ions as a function of energy have been measured. From these the self-sputtering ratios have been calculated. In the saturation region the amounts of material collected have been measured and the ranges of ions in graphite backings saturated with metal atoms have been calculated theoretically. This calculation gives an estimate of the metal atom concentrations in the graphite, which in turn determines the sputtering ratio of carbon.