Charge-Exchange Collisions Between Helium Ions and Cesium Vapor in the Energy Range 1.5-25 keV

Abstract

Charge-exchange collisions have been studied when ${\mathrm{He}}^{+}$ ions with an energy in the range 1.5-25 keV are incident on Cs vapor. Measurements of the positive, neutral, and negative beam components after passage through the target were made as a function of the Cs target density at twelve energies. Over the entire energy range studied, the negative fraction was found to reach a maximum and then decrease with increasing target density. The maximum yield of ${\mathrm{He}}^{-}$ ions was measured to be (1.4 ± 0.1)%. The maximum occurred at a ${\mathrm{He}}^{+}$ energy of 6 keV and a Cs target thickness of 5 × ${10}^{14}$ atoms/${\mathrm{cm}}^2$. Various cross sections relevant to the charge-exchange process were determined. At 10 keV the cross section for the production of a fast ${\mathrm{He}}^0$ atom from a ${\mathrm{He}}^{+}$ ion incident on Cs is (6.3 ± 0.6) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$, the value of the cross section for the production of a ${\mathrm{He}}^0$ atom when a ${\mathrm{He}}^{-}$ ion is incident on Cs is (1.0 ± 0.3) × ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$, and the value for the production of a ${\mathrm{He}}^{-}$ ion when a fast ${\mathrm{He}}^0$ atom in the (1s) (2s) ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ state is incident on Cs is (1.4 ± 0.4) × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$.