166 research outputs found
Descritpion of Exotic Nuclei Using Continuum Shell Model
In weakly bound exotic nuclei, number of excited bound states or narrow
resonances is small and, moreover, they couple strongly to the particle
continuum. Hence, these systems should be described in the quantum open system
formalism which does not artificially separate the subspaces of (quasi-) bound
and scattering states. The Shell Model Embedded in the Continuum provides a
novel approach which solves this problem. Examples of application in sd-shell
nuclei will be presented.Comment: Presented at the NATO Advanced Research Workshop Brijuni, Pula,
Croatia, June 2-5, 200
Role of the cooling rate in the stability of the superconducting phase of (TMTSF)_2ClO_4
The noncentrosymmetric ClO anions of the organic superconductor
(TMTSF)ClO order below 24K. The size of domains where the anions are
ordered is substantially dependent on the cooling rate which is a key parameter
for the stability of the low temperature electronic ground states. We study the
effect of the cooling rate on the SC phase within a self consistent approach in
the framework of the time dependent Ginzburg-Landau theory taking into account
the superconducting fluctuations. We derive the superconducting transition
temperature which is found to decrease with increasing cooling rate in
agreement with recent experimental data.Comment: 5 pages including one figure. Published online in Europhysics Letter
Gamow Shell Model Description of Neutron-Rich Nuclei
This work presents the first continuum shell-model study of weakly bound
neutron-rich nuclei involving multiconfiguration mixing. For the
single-particle basis, the complex-energy Berggren ensemble representing the
bound single-particle states, narrow resonances, and the non-resonant continuum
background is taken. Our shell-model Hamiltonian consists of a one-body finite
potential and a zero-range residual two-body interaction. The systems with two
valence neutrons are considered. The Gamow shell model, which is a
straightforward extension of the traditional shell model, is shown to be an
excellent tool for the microscopic description of weakly bound systems. It is
demonstrated that the residual interaction coupling to the particle continuum
is important; in some cases, it can give rise to the binding of a nucleus.Comment: 4 pages, More realistic s.p. energies used than in the precedent
versio
Dynamics of open quantum systems
The coupling between the states of a system and the continuum into which it
is embedded, induces correlations that are especially large in the short time
scale. These correlations cannot be calculated by using a statistical or
perturbational approach. They are, however, involved in an approach describing
structure and reaction aspects in a unified manner. Such a model is the SMEC
(shell model embedded in the continuum). Some characteristic results obtained
from SMEC as well as some aspects of the correlations induced by the coupling
to the continuum are discussed.Comment: 16 pages, 5 figure
Structure effects on the Coulomb dissociation of 8B at relativistic energies
We investigate the Coulomb dissociation of 8B on 208Pb target at the beam
energy of 250 MeV/nucleon, employing the cross sections for the radiative
capture reaction 7Be(p,gamma)8B calculated within the Shell Model Embedded in
the Continuum (SMEC) approach. In contrast to the situation at lower beam
energies, the Coulomb breakup cross sections are found to be sensitive to the
M1 transitions. Comparisons of SMEC and single-particle potential model
predictions show that the Coulomb breakup cross sections at these high energies
are sensitive to the structure model of 8B. Analysis of the preliminary data
taken recently at GSI reveal that E2 multipolarity contributes up to 25 % to
the cross sections even for the relative energies of p - 7Be below 0.25 MeV.Comment: 22 pages, 7 figure
Restoration of broken symmetries in Self-Consistent RPA
It is shown that the Self-Consistent RPA (SCRPA) approach allows in a very natural way to restore symmetries, spontaneously broken on the mean field level. This is achieved via the introduction of a second Lagrange multiplier which constrains the variance of the symmetry operator to zero. This important feature of SCRPA, here pointed out for the first time, is illustrated employing a simplified model of the nuclear superfluidity
A study of nuclei of astrophysical interest in the continuum shell model
We present here the first application of realistic shell model (SM) including
coupling between many-particle (quasi-)bound states and the continuum of
one-particle scattering states to the spectroscopy of 8B and to the calculation
of astrophysical factors in the reaction 7Be(p,gamma)8B.Comment: 9 pages incl. 3 figures, LaTeX with iopart class and epsf. Invited
talk at the Int. Workshop on Physics with Radioactive Nuclear Beams, Jan.
12-17, 1998, Puri, India. Shortened version will be published in proceedings
to apear as a separate J. Phys. G volum
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