Energy Shifts Observed in NiKX Rays Produced by Fission-Fragment Collisions

The $K\alpha$ and $K\beta$ x rays of Ni produced by the passage of light fission fragments from the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ through a thin Ni foil were found to be shifted up in energy by 69 ± 11 and 210 ± 16 eV, respectively, relative to the x rays produced by 6-MeV $\alpha$ particles and by photons from the decay of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$. These shifts are similar in character to those observed previously in 15- MeV oxygen-ion bombardments, but require extremely high ionic charge states to be explainable in terms of multiple inner-shell plus outer-shell ionization.