Charge-Exchange Collisions Between Hydrogen Ions and Cesium Vapor in the Energy Range 0.5-20 keV

Charge-exchange collisions have been studied when ${\mathrm{H}}^{+}$ ions and ground state ${\mathrm{H}}^0$ atoms 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 thickness at several energies between 0.5 and 20 keV. All three beam components were found to approach charge equilibrium monotonically. The maximum ${\mathrm{H}}^{-}$ equilibrium yield is (21 ± 4)%, which occurs at an ${\mathrm{H}}^{+}$ energy of 0.75 keV. The ${\mathrm{H}}^{-}$ yield decreases with increasing energy, and is 0.4% at 20 keV. At energies below 4 keV the ${\mathrm{H}}^{+}$ equilibrium yield is very small compared with the yield of ${\mathrm{H}}^0$ and ${\mathrm{H}}^{-}$. For energies greater than 10 kev the ${\mathrm{H}}^{-}$ equilibrium yield is very small compared with the yield of ${\mathrm{H}}^0$ and ${\mathrm{H}}^{+}$. The cross sections ${\sigma }_{+0\mathrm{}}$, ${\sigma }_{+-}$, ${\sigma }_{0+}$, and ${\sigma }_{0-}$ were measured. The subscripts + and - refer to the ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^{-}$ ions, 0 as an initial subscript refers to a ground-state ${\mathrm{H}}^0$ atom, and 0 as a final subscript refers to an ${\mathrm{H}}^0$ atom in the particular states produced. The cross section ${\sigma }_{+0\mathrm{}}$ decreases with increasing energy, and ranges from (9.4 ± 2.0) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 1 keV to (7.5 ± 1.1) × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 15 keV. The cross section ${\sigma }_{+-}$ decreases with increasing energy in the range 2-15 keV, and has the value (2.1 ± 0.6) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ at 5 keV. The cross section ${\sigma }_{0+}$ increases with increasing energy, having the value (1.2 ± 0.2) ×