1,135 research outputs found
The isovector effective charge and the staggering of the 2+ to 0+ transition probabilities in the Titanium isotopes
In an effort to understand the magical status of N=32 and N=34 at the very
neutron rich edge, experiments have been carried out in the Titanium isotopes
up to A=56. The measured staggering of the B(E2)'s is not reproduced by the
shell model calculations using the best effective interactions. We argue that
this may be related to the choice of the isovector effective charge and to the
value of the N=34 neutron gap.Comment: 2 pages, 2 figure
Shape Coexistence in 78 Ni and the new Island of Inversion
Large Scale Shell Model calculations (SM-CI) predict that the region of
deformation which comprises the heaviest Chromium and Iron isotopes at and
beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the
N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence
space including the full pf-shell for the protons and the full sdg shell for
the neutrons; which represents a comeback of the the harmonic oscillator shells
in the very neutron rich regime. The onset of deformation is understood in the
framework of the algebraic SU3-like structures linked to quadrupole dominance.
Our calculations preserve the doubly magic nature of the ground state of 78 Ni,
which, however, exhibits a well deformed prolate band at low excitation energy,
providing a striking example of shape coexistence far from stability
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
A Shell Model Description of the Decay Out of the Super-Deformed Band of 36Ar
Large scale shell model calculations in two major oscillator shells (sd and
pf) describe simultaneously the super-deformed excited band of 36Ar and its
low-lying states of dominant sd character. In addition, several two particle
two hole states and a side band of negative parity are also well reproduced. We
explain the appearance of the super-deformed band at such low excitation energy
as a consequence of the very large correlation energy of the configurations
with many particles and many holes (np-nh) relative to the normal filling of
the spherical mean field orbits (0p-0h). We study the mechanism of mixing
between these different configurations, to understand why the super-deformed
band survives and how it finally decays into the low-lying sd-dominated states
via the indirect mixing of the 0p-0h and 4p-4h configurations.Comment: 4 pages 5 figures, revtex4, revised version, minor change
Coexistence of spherical states with deformed and superdeformed bands in doubly magic 40-Ca; A shell model challenge
Large scale shell model calculations, with dimensions reaching 10**9, are
carried out to describe the recently observed deformed (ND) and superdeformed
(SD) bands based on the first and second excited 0+ states of 40-Ca at 3.35-MeV
and 5.21-MeV respectively. A valence space comprising two major oscillator
shells, sd and pf, can accommodate most of the relevant degrees of freedom of
this problem. The ND band is dominated by configurations with four particles
promoted to the pf-shell (4p-4h in short). The SD band by 8p-8h configurations.
The ground state of 40-Ca is strongly correlated, but the closed shell still
amounts to 65%. The energies of the bands are very well reproduced by the
calculations. The out-band transitions connecting the SD band with other states
are very small and depend on the details of the mixing among the different
np-nh configurations, in spite of that, the calculation describes them
reasonably. For the in-band transition probabilities along the SD band, we
predict a fairly constant transition quadrupole moment Q_0(t)~170 e fm**2 up to
J=10, that decreases toward the higher spins. We submit also that the J=8
states of the deformed and superdeformed band are maximally mixed.Comment: 12 pages, 9 figure
Shell model studies of neutron rich nuclei
We discuss the present status of the description of the structure of the very neutron rich nuclei, in the framework of modern large scale shell model calculations. Particular attention is paid to the interaction related issues, as well as to the problems of the shell model approach at the neutron drip line. We present detailed results for nuclei around N=20 and, more briefly, we discuss some salient features of the regions close to N=8, 28 and 40. We show that most experimental features can be understood in a shell model context
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
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