Ground-state properties of even-even N=Z nuclei within the Hartree-Fock-BCS and Higher Tamm-Dancoff approaches

We calculate the ground-state properties of well deformed, even-even N=Z nuclei in the region between Ni-56 and Sn-100 within two different approaches, focusing on the binding energy and deformation and pairing properties. First, we employ the Hartree-Fock-BCS (HFBCS) approximation with the Skyrme effective nucleon-nucleon interaction and discuss how the results depend on the parameterization of the interaction and on the pairing force parameters adjusted in various schemes to reproduce the experimental odd-even mass differences. Then, within the Higher Tamm-Dancoff Approximation (HTDA), which explicitly conserves the particle number, we calculate the same properties starting from the HFBCS solutions. The HTDA treatment of the ground-state correlations is converged within a n-particle-n-hole expansion using up to n=4 particle-hole excitations of the pair type (in the sense of Cooper pairs). We compare the ground-state properties calculated in these two descriptions of pairing correlations and deduce the importance of the particle-number conservation in weak pairing regimes. Finally, we extend the HTDA calculations so as to include the proton-neutron residual interaction and investigate the role of proton-neutron pairing on the above ground-state properties.Comment: 12 pages, 3 figures, 11 tables, submitted to Physical Review

Nuclear shell evolution and in-medium NN interaction

We report on a quantitative study of the evolution of the nuclear shell structure, in particular, effective single-particle energies (ESPEs), based on the spin-tensor decomposition of an effective two-body shell-model interaction. While the global trend of the ESPEs is mainly due to the central term of the effective interaction, variations of shell gaps invoke various components of the in-medium NN force. From a detailed analysis of a well-fitted realistic interaction in the sdpf shell-model space, two most important contributions for the evolution of the N = 20 and N = 28 shell gaps are confirmed to be the central term and the tensor term. The role of the latter is dominant to explain the energy shift of spin-orbit partners. Spin-tensor analysis of microscopic effective interactions in sd, pf, and gds shell-model spaces, contrasted with that of the phenomenologically adjusted ones, shows no evidence of amplification of the tensor component contribution; however, it points toward the neglect of three-body forces in the present microscopic interactions

The Nuclear Shell Model Toward the Drip Lines

We describe the "islands of inversion" that occur when approaching the neutron drip line around the magic numbers N=20, N=28 and N=40 in the framework of the Interacting Shell Model in very large valence spaces. We explain these configuration inversions (and the associated shape transitions) as the result of the competition between the spherical mean field (monopole) which favors magicity and the correlations (multipole) which favor deformed intruder states. We also show that the N=20 and N=28 islands are in reallity a single one, which for the Magnesium isotopes is limited by N=18 and N=32.Comment: Proceedings of the Nordic Conference in Nuclear Physics 2011, Stockholm, to appear in Physica Script

Large scale shell model calculations along Z=28 and N=50 closures: towards the doubly-magic 78Ni

We present the state-of-the art shell model calculations in a large model space (pf for protons, fpgd for neutrons), which allow to study simultaneously excitations across the Z=28 and N=50 shell gaps. We explore the region in the vicinity of 78Ni, being a subject of intense experimental investigations. Our calculations account correctly for the known low lying excited states in this region, including those which may correspond to cross-shell excitations. We observe the minimum of the N=50 mass gap at Z=32 consistent with experimental data and its further increase towards Z=28, indicating a robustness of the N=50 gap in 78Ni. The evolution of N=50 gap along the nickel chain is shown to bear similarities with what is know in oxygen and calcium chains, providing a new opportunity for the studies of 3-body monopole effects in medium mass nuclei.Comment: 5 pages, 5 fugure

Shell-model half-lives for r-process waiting point nuclei including first-forbidden contributions

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilities of the r-process waiting point nuclei at the magic neutron numbers N=50, 82, and 126. The calculations include contributions from allowed Gamow-Teller and first-forbidden transitions. We find good agreement with the measured half-lives for the N=50 nuclei with charge numbers Z=28-32 and for the N=82 nuclei 129Ag and 130Cd. The contribution of forbidden transitions reduce the half-lives of the N=126 waiting point nuclei significantly, while they have only a small effect on the half-lives of the N=50 and 82 r-process nuclei.Comment: 14 pages, 17 figures, submitted to Phys. Rev.

State dependent δ\delta-pairing and spontaneous fission

We examine the fission barriers, mass parameters and spontaneous fission half lives of fermium isotopes within the framework of macroscopic-microscopic model with a $\delta$-pairing interaction. Four different macroscopic models are applied and studied. The results are compared to experimental data and to the corresponding monopole pairing ones. The half lives obtained in the $\delta$-pairing model are comparable with experimental data. The state-dependence of pairing has an important effect on the calculated fission half-lives.Comment: Proceedings of 10th Nuclear Physics Workshop, Kazimierz Dolny, Poland, September 24-28, 2003; Latex2e; 4 figure

Influence of plastic deformation on the change of electrical and mechanical properties oxygen-free (OF) copper and copper alloy wires

This article is devoted to the comparison of changes in mechanical and electrical properties due to the applied deformation of copper and copper alloy rods. Bars from four different production technologies were deformed in the drawing process, including oxygen-free (OF) copper, electrolytic copper ETP, copper from cable granulate and silver copper with a high silver content up to 15 wt. % obtained in laboratory technology. The article presents the chemical purity, physical and electrical properties of rods before deformation. The summary of the research on the selected materials are changes in mechanical properties and electrical conductivity as a function of deformation up to 3,5 on a logarithmic scale and the coefficient of electromechanical efficiency WEM