Ionization of relativistic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>K</mml:mi></mml:math>-shell electrons by proton bombardment

Abstract

$K$-shell ionization cross sections for Ho, Au, and U by proton impact have been measured over the incident energy range 1-4 MeV. The measured cross sections are larger than those predicted from the plane-wave Born, semiclassical, and binary-encounter approximations including Coulomb-deflection and binding-energy effects by factors from 2 to 20. However, it is shown that these large disagreements can be well explained by the semiclassical theory using relativistic wave functions for the $K$-shell electrons. The validity of various approximate estimations of electronic relativistic effects is discussed. Some results on $^{3}\mathrm{He}$-ion impact are also discussed. Ratios of x-ray production cross sections for $K{\ensuremath{\alpha}}_{2}$, $K{\ensuremath{\beta}}_{1}$, and $K{\ensuremath{\beta}}_{2}$ lines to that of $K{\ensuremath{\alpha}}_{1}$ line are shown as a function of proton energy and the results indicate little simultaneous ionization probability in the $L$, $M$, and $N$ shells of heavy atoms.