Experiments on Charge-Changing Collisions of Lithium Ionic and Atomic Beams

Abstract

Beams of ${\mathrm{Li}}^{+}$ ions accelerated to kinetic energies in the range 10-475 kev were brought into charge equilibrium in the gases ${\mathrm{H}}_{2}$, He, and ${\mathrm{N}}_{2}$ and the fractional amounts of ${\mathrm{Li}}^{\ensuremath{-}}$, ${\mathrm{Li}}^{0}$, ${\mathrm{Li}}^{+}$, ${\mathrm{Li}}^{++}$, ${\mathrm{Li}}^{+++}$ measured. Because of the relatively large amount of ${\mathrm{Li}}^{\ensuremath{-}}$ in an equilibrated beam below 40 kev in energy in propane and nitrous oxide, limited investigations were carried out in these gases. The anomalously large ${\mathrm{Li}}^{++}$ yield in helium at ${\mathrm{Li}}^{7}$ energies below 100 kev was noted.By holding each separated charged constituent successively in an orbit in a magnetic field, admitting gas, and observing the beam attenuation, the total cross section for all charge-changing collisions was observed. Through application of the differential equations for growth or decay of a charged component, certain individual charge-changing cross sections can be deduced from these observed sums. Values are given for (${\ensuremath{\sigma}}_{\overline{1}0}+{\ensuremath{\sigma}}_{\overline{1}1}$), ${\ensuremath{\sigma}}_{01}$, ${\ensuremath{\sigma}}_{10}$, ${\ensuremath{\sigma}}_{12}$, ${\ensuremath{\sigma}}_{21}$, and (${\ensuremath{\sigma}}_{32}+{\ensuremath{\sigma}}_{31}$) in ${\mathrm{H}}_{2}$, He, and ${\mathrm{N}}_{2}$ target gases throughout the energy range. Upper limits can be assigned to ${\ensuremath{\sigma}}_{0\overline{1}}$, ${\ensuremath{\sigma}}_{1\overline{1}}$, ${\ensuremath{\sigma}}_{13}$, and ${\ensuremath{\sigma}}_{23}$. Use of data on ${\ensuremath{\sigma}}_{1\overline{1}}$ in ${\mathrm{H}}_{2}$ from other sources provides values of ${\ensuremath{\sigma}}_{0\overline{1}}$ in that gas. Values for ${\ensuremath{\sigma}}_{21}$ for ${\mathrm{Li}}^{++}$ in helium gas, compared, at common velocities, with ${\ensuremath{\sigma}}_{10}$ for ${\mathrm{He}}^{+}$ in helium, and ${\ensuremath{\sigma}}_{0\overline{1}}$ for ${\mathrm{H}}^{0}$ in helium, show the exchange nature of the ${\mathrm{He}}^{+}$He interaction compared to that of the other isoelectronic structures.