The characteristic $K\beta$ x rays produced by 15.0-MeV oxygen (${\mathrm{O}}^{4+}$) ions on Ni are found to shift in the spectrum by 112±15 eV relative to the energies produced by x-ray and proton excitation in Ni. Similarly, in Cu an energy shift of 97 ± 15 eV is observed. The observed shift is possibly due to the larger $K\beta$ energies of the multiply ionized Ni or Cu produced in ${\mathrm{O}}^{4+}$ bombardments as opposed to the singly ionized Cu or Ni $K\beta$ x rays.

• Received 5 September 1969

DOI:https://doi.org/10.1103/PhysRevLett.23.1009