Resonant inelastic x-ray spectroscopy on UO₂ as a test case for actinide materials

Abstract

Resonant inelastic x-ray spectroscopy at the uranium N₄ absorption edge at 778 eV has been used to reveal the excitations in UO₂ up to 1 eV. The earlier (1989) studies by neutron inelastic scattering of the crystal-field states within the ³H₄ multiplet are confirmed. In addition, the first excited state of the ³F₂ multiplet at ∼520 meV has been established, and there is a weak signal corresponding to the next excited state at ∼920 meV. This represents a successful application of soft x-ray spectroscopy to an actinide sample, and resolves an open question in UO₂ that has been discussed for 50 years. The technique is described and important caveats are drawn about possible future applications.