Experimental Electron-Transfer Cross Sections for Fluorine Ions in Argon at Energies from 8 to 54 MeV

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Abstract
Electron-capture and -loss cross sections have been measured for fluorine ions passing through argon gas in the energy range from 8 to 54 MeV. Cross sections for single- and multiple-electron capture and loss in a single collision were obtained using a computer analysis in real time for fitting the data with an iterative procedure. A detailed description of the computer analysis is given. The capture of as many as four electrons in a single collision has been observed in several cases. The velocity dependence of the single-capture cross section is described by a power of velocity with the power generally increasing for lower-incident-charge states. For multiple-capture processes the cross section decreases more rapidly than a power of velocity. The capture cross section for the fully stripped fluorine nucleus amounts to less than 50% of the theoretical predictions of Nikolaev scaled from a Brinkman-Kramers calculation for protons in argon. The ratio of double- to single-electron-capture cross sections has been discussed in terms of a geometry-independent component of the capture process. The maxima observed in this ratio were rather sharp and close to the same energy for all incident-charge states, making it impossible to identify from the excitation functions the specific shells involved in the capture process. Electron-loss cross sections generally exhibit a broad maximum at velocities approximately twice the orbital velocity of the electron that is lost in the collision. The velocity dependence of multiple-loss cross sections is generally not similar to those for single loss.