Radiative electron capture for F/sup 8 +/ and F/sup 9 +/ ions in collisions with a He gas target
The x rays from the radiative electron capture (REC) to the projectile K-shell were investigated for F/sup 8 +/ and F/sup 9 +/ ions incident on the He target atoms in the projectile energy range from 15 to 40 MeV. The peak energies of the K-REC x-ray spectra were found to decrease linearly with a decrease of the projectile energies as expected and extrapolated to the correct ls binding energies at zero velocity. According to theory the distribution width of the REC energies should be independent of the binding energy of electrons in the projectile ions. However, it is found that this width for F/sup 8 +/ ions is systematically smaller by 20% than that for F/sup 9 +/ ions. The measured REC cross sections for F/sup 9 +/ ions are slightly larger than twice those for F/sup 8 +/ ions and the total REC cross sections for F/sup 8 +/ and F/sup 9 +/ ions were found to be more than three orders of magnitude smaller than the total electron capture cross sections and the capture cross sections into excited states.