Production and Loss of Fast Metastable Helium Atoms in Collisions with Xe,H2, Ar, and He

Abstract

Cross sections for production and destruction of fast ${\mathrm{He}}^0$ atoms in triplet states have been measured for 10- to 30-keV ${\mathrm{He}}^{+}$ ions incident on gas targets of Xe, ${\mathrm{H}}_2$, Ar, and He. In a Cs vapor the production of positive and negative ions of He is sensitive to the fraction of metastable triplet atoms in the incident ${\mathrm{He}}^0$ beam so that it is possible to use a thin Cs vapor target to analyze the fraction of triplet metastable atoms among the fast ${\mathrm{He}}^0$ atoms emerging from the gas target of Xe, ${\mathrm{H}}_2$, Ar, or He. The fraction of neutral ${\mathrm{He}}^0$ atoms in the triplet metastable state emerging from thin targets of Xe, ${\mathrm{H}}_2$, Ar, and He are 0.19±0.07, 0.08±0.04, 0.05±0.02, and ${\mathrm{He}}^{+}$ energies of 25 keV.