Direct ionization and electron capture inM-shell x-ray production by fluorine ions

Abstract

Measurements of $M$-shell x-ray production cross sections are reported for thin solid targets of $_{79}\mathrm{Au}$, $_{83}\mathrm{Bi}$, and $_{92}\mathrm{U}$. Fluorine ions of energies 25, 27, and 35 MeV and charge states of 4, 5, 6, 8, and 9 were used. The microscopic cross sections were determined from measurements made with targets ranging in thickness from \ensuremath{\sim}1 to \ensuremath{\sim}300 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$. An enhancement in the target $M$-shell x-ray production cross section was observed for fluorine ions with one or two $K$-shell vacancies over those without a $K$-shell vacancy. The sums of cross sections for direct ionization to the target continuum and electron capture to the projectile's $L,M,N,\dots{}$ shells are inferred from charge state $q=4,5,6$ data. The first Born calculations overpredict the cross-section data at all energies. Cross sections for electron capture from the target $M$ shell to the projectile $K$ shell for one ($q=8$) and two ($q=9$) $K$-shell vacancies in the projectile are also overpredicted by the first Born approximation for electron capture, i.e., the Oppenheimer-Brinkman-Kramers approximation of Nikolaev. The data are in good agreement with the ECPSSR theory of Brandt and Lapicki, which accounts for the energy-loss, Coulomb-deflection, and relativistic effects in the perturbed-stationary-state theory.