Measurements of 3d-5f and 3d-6f transition energies in nickel-like ions for resonant photopumping by helium-like ions

The 3d-5f and 3d-6f transition energies of several Ni-like ions were measured to study their suitability for use in an X-ray laser scheme that uses He-like K-shell transitions for resonant photopumping. Specifically, 19 transitions in Ag19+, Sn22+, Pr31+, Gd36+, Yb42+, Ta45+, Ir49+, Th62+ and U64+ were measured and compared to 2p-1s transitions in F7+, Ne8+, Si12+, S14+, Cl15+, Ar16+, Ti20+ and V21+. The best resonance found was for the F He-like 21P1-11S0 transition pumping the Ag Ni-like 3d3/2-6f5/2 transition at 737.6 eV. The energy difference of 0.14 (24)eV corresponds to a 190-ppm resonance. An energy shift between the theoretical and measured energies of 3d5/2-6f7/2 transitions is confirmed by the present measurements; a similar effect is also observed in the 3d3/2-5f5/2, 3d5/2-5f7/2 and 3d3/2-6f5/2 transitions. (orig.)