XUV emission from uranium plasmas; the identification of U XIII and U XV

The XUV spectra of uranium in different regimes of conical thickness and in different ion stages have been observed in a laser-produced plasma. The spectra are dominated by 5d-5f transitions which produce an intense compact transition array in the 100 AA region. The profile and extent of this array is strongly sensitive to the density of uranium ions present in the plasma. A number of lines arising from 5d 10 to 5d 9 nl transitions in U VIII and U XV are identified with the aid of Hartree-Fock and Dirac-Fock calculations. The similarities between the spectrum of uranium and those of the lanthanides observed under similar conditions are stressed.