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

Beams of Li⁺ ions accelerated to kinetic energies in the range 10-475 kev were brought into charge equilibrium in the gases H₂, He, and N₂ and the fractional amounts of Li^-, Li⁰, Li⁺, Li⁺⁺, Li⁺⁺⁺ measured. Because of the relatively large amount of Li^- 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 Li⁺⁺ yield in helium at Li⁷ 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 (σ1̄0+σ1̄1), σ₀₁, σ₁₀, σ₁₂, σ₂₁, and (σ₃₂+σ₃₁) in H₂, He, and N₂ target gases throughout the energy range. Upper limits can be assigned to σ01̄, σ11̄, σ₁₃, and σ₂₃. Use of data on σ11̄ in H₂ from other sources provides values of σ01̄ in that gas. Values for σ₂₁ for Li⁺⁺ in helium gas, compared, at common velocities, with σ₁₀ for He⁺ in helium, and σ01̄ for H⁰ in helium, show the exchange nature of the He⁺He interaction compared to that of the other isoelectronic structures.