Formation of metastable hydrogen atoms by charge exchange of fast protons in magnesium and barium vapors
- 1 June 1979
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review A
- Vol. 19 (6), 2185-2191
- https://doi.org/10.1103/physreva.19.2185
Abstract
The cross sections for the formation of metastable atoms in collisions with Mg and Ba alkaline-earth-metal vapors have been measured over the energy range 1.5-90 keV. The absolute value of the cross sections has been obtained by normalizing the present results to the cross section for formation in Ar gas at 30 keV. In Ba, the cross section reaches a maximum value of 5.6 × at 3 keV. In Mg, the maximum value is 3.2 × and occurs at 7 keV. The measured cross sections exhibit structure at high energies which is attributed to inner-shell capture. A comparison of the present results with previous electron-capture data in Mg indicates that the capture law is not obeyed. An analysis based on data available for 16 different collisions between ions and and targets shows that the scaling law for the velocity at which the single-electron-capture cross section is a maximum is not consistent with the Massey adiabatic criterion. Instead, the data are consistent with the relation where is the energy defect of the collision. The fraction of the neutral beam in the state formed by collisions of ions with thin targets of Mg and Ba is also reported. In Ba, the fraction is equal to 0.25 ± 0.05 at 2.0 keV and is rising at low energies. In Mg, the maximum value of the fraction is 0.13 ± 0.03 and occurs at ∼ 7 keV.
Keywords
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