Radiative Electron Capture for F8+ and F9+ 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 F8+ and F9+ 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, ΓREC, of the REC energies should be independent of the binding energy of electrons in the projectile ions. However, it is found that ΓREC for F8+ ions is systematically smaller by 20% than that for F9+ ions. The measured REC cross sections for F9+ ions are slightly larger than twice those for F8+ ions and the total REC cross sections for F8+ and F9+ 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.