Single-particle spectra, pairing correlations and spectroscopic properties of actinide and heavier nuclei

We discuss the relevance of the single-particle (sp) properties of the well studied Skyrme SIII interaction to describe some spectroscopic properties of heavy nuclei within self-consistent Hartree-Fock plus BCS calculations (with blocking when needed), using a simple seniority pairing residual interaction (V_res). To fit V_res we took stock of the excellent consistency found in the rare-earth region between its adjustment to both moments of inertia (MoI) of well-deformed nuclei and oddeven mass differences. For simplicity reasons we thus made a fit on MoI. Our sample of nuclei was defined by all even-even isotopes of actinide and heavier elements, with two criteria: i) be well and rigidly deformed in their ground states, as assessed by a ratio E(4⁺₁ )/E(2⁺₁ ) > 3:2, ii) present some isomeric activity with suggested isomeric energy (EIS) and spin/parity characterization. We have thus considered 14 actinide isotopes (from Uranium to Nobelium) plus ²⁵⁶Rf. With a simple law of variation of the pairing matrix elements according to N or Z, we get a fair reproduction of MoI except around the neutron number N = 152 where SIII exaggerates its well documented magicity (for normally deformed solutions). Such a study of MoI assesses thus also the sp spectra, of which a further evaluation of the quality is provided by the comparison of the corresponding experimental and theoretical E_IS. Our calculations were limited to quasi-particle (uncoupled) configuration of the seniority 2 type. Preliminary results on some isomeric states of the considered isotopes will be discussed particularly by comparing them with those obtained in a particle number conserving approach. Key Words: Actinide nuclei, single-particle spectra, pairing correlations. (author)