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Resonant inelastic x-ray scattering (RIXS) using an incident energy tuned to the uraniumN4,5absorption edges is reported from epitaxial films of α -U 3 O 8 and UN. Theory shows that for U 3 O 8 the multiplets associated with a 5 f 1 configuration with a ground state of2F5/2and the excited state of2F7/2are observed. However, the strong transition predicted at a transfer energy of 1.67 eV is not observed. We assume this is a consequence of the intermediate state lifetime broadening due to interaction with continuum states when the transferred energy exceeds the onset of the continuum in the presence of the core hole. This hypothesis is supported by the results obtained for the 5 f -itinerant system UN, where no sharp transitions have been observed, although the broad scattering response centred at ∼1 eV is considered a signature of a predominantly 5 f 3 configuration in this band-like semi-metallic system. These experiments and theory add important information on these materials, both of which have been investigated since the 1960s, as well as whether RIXS at the uranium N edge can become a valuable tool for actinide research., (© 2023 IOP Publishing Ltd.)

Resonant inelastic x-ray spectroscopy at the uranium N 4 absorption edge at 778 eV has been used to reveal the excitations in UO 2 up to 1 eV. The earlier (1989) studies by neutron inelastic scattering of the crystal-field states within the 3 H 4 multiplet are confirmed. In addition, the first excited state of the 3 F 2 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 UO 2 that has been discussed for 50 years. The technique is described and important caveats are drawn about possible future applications.

X-ray diffraction, specific heat, magnetic susceptibility and inelastic x-ray scattering measurements on the transurarium oxypnictides NpFeAsO and NpFeAsO0.85F0.15 are presented. No superconductivity down to 2 K was observed upon fluorine doping, contrary to the structurally analogous rare-earth pnictides. No modification of the phonon density of states was observed upon doping with fluorine. We discuss our results in light of the latest experimental and theoretical studies on the role of phonons in the superconducting pnictide compounds.