Measurements on Charge-Changing Collisions Involving Negative Hydrogen, Helium, and Oxygen Ions

Abstract

The determination of charge-changing collision cross sections for negative ions involves making measurements on other beam components as well. Beams of ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{+}$, and ${\mathrm{O}}^{+}$ were sent through a gas cell where charge exchange took place. Ratios of various charge components were obtained for thick targets. Negativeion beams were sent through thin targets in a magnetic field and attenuation ratios were determined. Measurements were in the energy range from 10 to 400 keV. The observations on equilibrium ratios for hydrogen ions in various gases were in excellent agreement with previous work. Some new values of ${\sigma }_{0\overline{1}}$ and ${\sigma }_{\overline{1}0}+{\sigma }_{\overline{1}1}$ for a hydrogen-gas target are presented. (${\sigma }_{0\overline{1}}=\mathrm{cross}\mathrm{section}\mathrm{a}\mathrm{change}\mathrm{from}\mathrm{charge}0\mathrm{t}\mathrm{o}-1,\mathrm{e}\mathrm{t}\mathrm{c}.\mathrm{}$) The observations on the helium beam were limited to the beam-fraction ratio $\frac{F_{\overline{1}}}{F_1}$. This ratio did not approach an equilibrium value, except in the case of the helium target, but rather reached a maximum and continued to decrease for thicker targets. The maximum values of $\frac{F_{\overline{1}}}{F_1}$ are presented for gas targets of hydrogen, helium, nitrogen, oxygen, and argon. The values of ${\sigma }_{\overline{1}0}+{\sigma }_{\overline{1}1}$ are given for a hydrogen target and values of ${\sigma }_{0\overline{1}}$ determined with the aid of previously published data are presented. The observations on the oxygen beam allowed the determinations of beam fractions $F_{\overline{1}\infty }$, $F_{0\infty }$, $F_{1\infty }$, $F_{2\infty }$, $F_{3\infty }$ for hydrogen, helium, and oxygen targets. Using these quantities it was possible to determine certain individual charge-changing cross sections after making simplifying assumptions concerning the negligible magnitude of some of the cross sections. These cross sections and the beam fractions are presented for the three gases.