570 research outputs found

### Generalization of the $N_pN_n$ Scheme and the Structure of the Valence Space

The $N_pN_n$ scheme, which has been extensively applied to even-even nuclei,
is found to be a very good benchmark for odd-even, even-odd, and doubly-odd
nuclei as well. There are no apparent shifts in the correlations for these four
classes of nuclei. The compact correlations highlight the deviant behavior of
the Z=78 nuclei, are used to deduce effective valence proton numbers near Z=64,
and to study the evolution of the Z=64 subshell gap.Comment: 10 pages, 4 figure

### SU(3) quasidynamical symmetry underlying the Alhassid--Whelan arc of regularity

The first example of an empirically manifested quasi dynamical symmetry
trajectory in the interior of the symmetry triangle of the Interacting Boson
Approximation model is identified for large boson numbers. Along this curve,
extending from SU(3) to near the critical line of the first order phase
transition, spectra exhibit nearly the same degeneracies that characterize the
low energy levels of SU(3). This trajectory also lies close to the
Alhassid-Whelan arc of regularity, the unique interior region of regular
behavior connecting the SU(3) and U(5) vertices, thus offering a possible
symmetry-based interpretation of that narrow zone of regularity amidst regions
of more chaotic spectra.Comment: 4 pages, LaTeX, 5 eps figure

### Quadrupole collectivity in random two-body ensembles

We conduct a systematic investigation of the nuclear collective dynamics that
emerges in systems with random two-body interactions. We explore the
development of the mean field and study its geometry. We investigate multipole
collectivities in the many-body spectra and their dependence on the underlying
two-body interaction Hamiltonian. The quadrupole-quadrupole interaction
component appears to be dynamically dominating in two-body random ensembles.
This quadrupole coherence leads to rotational spectral features and thus
suggests the formation of the deformed mean-field of a specific geometry

### Evolution of the N=50 gap from Z=30 to Z=38 and extrapolation towards 78Ni

The evolution of the N=50 gap is analyzed as a function of the occupation of
the proton f5/2 and p3/2 orbits. It is based on experimental atomic masses,
using three different methods of one or two-neutron separation energies of
ground or isomeric states. We show that the effect of correlations, which is
maximized at Z=32 could be misleading with respect to the determination of the
size of the shell gap, especially when using the method with two-neutron
separation energies. From the methods that are the least perturbed by
correlations, we estimate the N=50 spherical shell gap in 78Ni. Whether 78Ni
would be a rigid spherical or deformed nucleus is discussed in comparison with
other nuclei in which similar nucleon-nucleon forces are at play.Comment: 7 pages, 8 figures, accepted for publication PRC (22 december 2011

### IBM-1 calculations towards the neutron-rich nucleus $^{106}$Zr

The neutron-rich N=66 isotonic and A=106 isobaric chains, covering regions
with varying types of collectivity, are interpreted in the framework of the
interacting boson model. Level energies and electric quadrupole transition
probabilities are compared with available experimental information. The
calculations for the known nuclei in the two chains are extrapolated towards
the neutron-rich nucleus $^{106}$Zr.Comment: 5 pages, 2 figures, 6 tables, to be published in Phys. Rev.

### New magic number for neutron rich Sn isotopes

The variation of E(2+_1) of (134-140)Sn calculated with empirical SMPN
interaction has striking similarity with that of experimental E(2+_1) of
even-even (18-22)O and (42-48)Ca, showing clearly that N=84-88 spectra exhibit
the effect of gradual filling up of \nu(2f_{7/2}) orbital which finally
culminates in a new shell closure at N=90. Realistic two-body interaction CWG
does not show this feature. Spin-tensor decomposition of SMPN and CWG
interactions and variation of their components with valence neutron number
reveals that the origin of the shell closure at 140Sn lies in the three body
effects. Calculations with CWG3, which is obtained by including a simple
three-body monopole term in the CWG interaction, predict decreasing E(2+_1) for
(134-138)Sn and a shell closure at 140Sn.Comment: 4 pages, 5 figure

- â€¦