Charge-changing collisions involving fast helium beams - the effect of a metastable atom component

Abstract

Cross sections ?10 and ?01 for one-electron capture and loss have been determined in the energy range 60-400 kev by studying, respectively, the charge neutralization and stripping of helium ion and atom beams during passage through `thin' targets of hydrogen and helium In the studies of electron loss, measurements made with helium atom beams prepared by charge-transfer neutralization of He+ ions during passage through various `thick' gaseous targets were found to yield apparent cross sections ?01 which were dependent on the particular neutralizer gas. For example, in the energy range investigated, values of ?01 for helium atoms in hydrogen were found to increase by between 18% and 40% when hydrogen was substituted for helium as the neutralizer gas, an effect believed to be due to the formation of an increased fraction of metastable helium atoms in the fast beam. The apparently strong influence of a helium metastable atom component in this case suggests that a satisfactory description of the charge equilibriation of fast helium beams during passage through thick gaseous targets cannot always be given in terms of a simple three-component system Previous data on electron capture and loss obtained by the use of such a treatment must therefore be interpreted with extreme care