Scattering of neutrons and synchrotron x-rays as probes of 5f electron behavior

The behavior of 5f electrons varies from localized (almost non-bonding) in UO2 to strongly itinerant (and bonding) in the elements up to Am and in many intermetallic compounds. This paper will discuss the contribution of the scattering of neutrons and photons to the understanding of the nature of the 5f states. An important example was the discovery of the charge-density wave in α-uranium, and the ongoing theoretical and experimental development. Probing magnetism, both static magnetization distributions as well as the dynamic behavior, is a forte of neutrons. Central to progress has been the theory treating the orbital moment within the LDA method leading to the predictions of orbital and spin cancellation (e.g. as seen with neutrons in Pu compounds and UFe2), and efforts to understand the roles of the spin-orbit interaction and hybridization in the dynamic magnetic response. Synchrotrons offer a new perspective, especially since they use minute amounts of material. Some of our recent advances in both structural studies under pressure and exploiting resonant effects will be reviewed. (author)