nuclear physics in poland 1996 – 2006

HIGH SPIN STATES OF STRONGLY DEFORMED CONFIGURATIONSIN MEDIUM-MASS NUCLEIJ. Dobaczewski 1 , W. Nazarewicz 1,2,3 , W. Satuła 1 , T.R. Werner 11 Institute of Theoretical Physics, Warsaw University, Warszawa2 Oak Ridge National Laboratory, Oak Ridge, USA3 Department of Physics, University of Tennessee, Knoxville, USAMagic and doubly magic nuclei and their nearbyneighbors play a special role in our quest forunderstanding nuclear structure. Informationobtained for these nuclei, both experimental andtheoretical, is intensively used for determinationof single-particle energies needed, e.g., for largescalecalculations within the shell model; it alsoprovides estimates of two-body matrix elementsof the residual interactions which enter this kindof calculations. Properties of these nuclei havealways been used in procedures of fittingparameters in various theoretical models, like,e.g., simple independent particle models ofNilsson or Woods-Saxon type or more involvedmean-field approaches like those based onHartree-Fock (HF) or Hartree-Fock-Bogoliubov(HFB) equations, Relativistic Mean Field (RMF)methods, Monte Carlo shell models, etc. [1,2].The region around doubly magic 56 Ni nucleus isof particular interest. Nuclei in this region (Fe, Co,Ni, Cu, Zn) have intermediate masses which arelarge enough to induce pronounced collectivephenomena, but still sufficiently small to makethese nuclei amenable to “low-level” microscopictheoretical treatment. Since proton and neutronnumbers are similar (Z ≈ N), valence nucleons canoccupy the same subshells and, as the mass is stillnot too large, their spatial distributions can alsobe very close: this can lead to manifestations ofT=0 channel of pairing interactions. In addition,neutron and proton shell effects can actcoherently, what results in particularly reachpattern of shape coexistence and shape transitions— these shapes range from spherical to triaxialand superdeformed (with deformation up to β 2 ≈0.5) and can be alternatively described by varioustheoretical models: particle-hole excitationswithin shell model, minima in the total Routhiansurfaces in Strutinsky-Woods-Saxon cranking calculations,special configurations of alpha clusters,etc. Peculiarities of this region of nuclei makes itparticularly well suited for analyzing theinterplay between T=0 and T=1 channels of thepairing interactions; while the T=1 component isquickly quenched by high frequency rotation, theT=0 component should survive longer [5,8].In our studies we used mainly the Skyrme-Hartree-Fock (and/or HFB) cranking approach, aswell as independent particle model of Woods-Saxon type (with cranking and shell and pairingcorrections taken into account) [2-8]. In thesemodels (as well as in the shell model), high spinstates of low-isospin nuclei in the A ≈ 60 regioncan be described as multi-particle-multi-holeconfigurations involving f 7/2 hole and g 9/2 particleorbitals (i.e., excitations across N = Z = 28 shellgap). Dynamic moments of inertia, alignments,branching ratios and other observable quantitiesare highly sensitive to assumed physical scenariosand details of models used for interpreting theexperimental findings; this gives us a possibilityto “fine tune” our models and to understandbetter the physics behind phenomena observed inexperiments.J (2) --(h 2 /MeV)Relative alignment252015106420EXP[4 3 4 2 ][4 2 4 2 ]HF+SLy40 0.5 1 1.5 2EXP[4 3 4 2 ][4 2 4 2 ]CZ1327777Z1227A77(a)(b)61Zn61Zn – 58 Cu0.6 0.8 1 1.2 1.4Rotational frequency (MeV)Fig. Dynamic moments of inertia, J (2) , of the super-deformed band in61Zn (a) and its relative alignment with respect to SD bands in 58 Cu(b). Two different configurations are compared with experimentalresults. From Ref. [5].83