4,823 research outputs found

### Gamow-Teller GT+ distributions in nuclei with mass A=90-97

We investigate the Gamow-Teller strength distributions in the
electron-capture direction in nuclei having mass A=90-97, assuming a 88Sr core
and using a realistic interaction that reasonably reproduces nuclear
spectroscopy for a wide range of nuclei in the region as well as experimental
data on Gamow-Teller strength distributions. We discuss the systematics of the
distributions and their centroids. We also predict the strength distributions
for several nuclei involving stable isotopes that should be experimentally
accessible for one-particle exchange reactions in the near future.Comment: 9 pages, 10 figures (from 17 eps files), to be submitted to
Phys.Rev.C; corrected typos, minor language change

### The Cranked Nilsson-Strutinsky versus the Spherical Shell Model: A Comparative Study of pf-Shell Nuclei

A comparative study is performed of a deformed mean field theory, represented
by the cranked Nilsson-Strutinsky (CNS) model, and the spherical shell model.
Energy spectra, occupation numbers, B(E2)-values, and spectroscopic quadrupole
moments in the light pf shell nuclei are calculated in the two models and
compared. The result is also compared to available experimental data which are
generally well described by the shell model. Although the Nilsson-Strutinsky
calculation does not include pairing, both the subshell occupation numbers and
quadrupole properties are found to be rather similar in the two models. It is
also shown that ``unpaired'' shell model calculations produce very similar
energies as the CNS at all spins. The role of the pairing energy in the
description of backbending and signature splitting in odd-mass nuclei is also
discussed.Comment: 14 pages, 20 figures, submitted to Phys.Rev.

### Improved estimate of electron capture rates on nuclei during stellar core collapse

Electron captures on nuclei play an important role in the dynamics of the
collapsing core of a massive star that leads to a supernova explosion. Recent
calculations of these capture rates were based on microscopic models which
account for relevant degrees of freedom. Due to computational restrictions such
calculations were limited to a modest number of nuclei, mainly in the mass
range A=45-110. Recent supernova simulations show that this pool of nuclei,
however, omits the very neutron-rich and heavy nuclei which dominate the
nuclear composition during the last phase of the collapse before neutrino
trapping. Assuming that the composition is given by Nuclear Statistical
Equilibrium we present here electron capture rates for collapse conditions
derived from individual rates for roughly 2700 individual nuclei. For those
nuclei which dominate in the early stage of the collapse, the individual rates
are derived within the framework of microscopic models, while for the nuclei
which dominate at high densities we have derived the rates based on the Random
Phase Approximation with a global parametrization of the single particle
occupation numbers. In addition, we have improved previous rate evaluations by
properly including screening corrections to the reaction rates into account.Comment: 32 pages, 13 figures, 1 table; elsart; to appear in Nuclear Physics

### Shape transition and oblate-prolate coexistence in N=Z fpg-shell nuclei

Nuclear shape transition and oblate-prolate coexistence in $N=Z$ nuclei are
investigated within the configuration space ($2p_{3/2}$, $1f_{5/2}$,
$2p_{1/2}$, and $1g_{9/2}$). We perform shell model calculations for $^{60}$Zn,
$^{64}$Ge, and $^{68}$Se and constrained Hartree-Fock (CHF) calculations for
$^{60}$Zn, $^{64}$Ge, $^{68}$Se, and $^{72}$Kr, employing an effective pairing
plus quadrupole residual interaction with monopole interactions. The shell
model calculations reproduce well the experimental energy levels of these
nuclei. From the analysis of potential energy surface in the CHF calculations,
we found shape transition from prolate to oblate deformation in these $N=Z$
nuclei and oblate-prolate coexistence at $^{68}$Se. The ground state of
$^{68}$Se has oblate shape, while the shape of $^{60}$Zn and $^{64}$Ge are
prolate. It is shown that the isovector matrix elements between $f_{5/2}$ and
$p_{1/2}$ orbits cause the oblate deformation for $^{68}$Se, and four-particle
four-hole ($4p-4h$) excitations are important for the oblate configuration.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.

### Effects of Inelastic Neutrino-Nucleus Scattering on Supernova Dynamics and Radiated Neutrino Spectra

Based on the shell model for Gamow-Teller and the Random Phase Approximation
for forbidden transitions, we have calculated reaction rates for inelastic
neutrino-nucleus scattering (INNS) under supernova (SN) conditions, assuming a
matter composition given by Nuclear Statistical Equilibrium. The rates have
been incorporated into state-of-the-art stellar core-collapse simulations with
detailed energy-dependent neutrino transport. While no significant effect on
the SN dynamics is observed, INNS increases the neutrino opacities noticeably
and strongly reduces the high-energy tail of the neutrino spectrum emitted in
the neutrino burst at shock breakout. Relatedly the expected event rates for
the observation of such neutrinos by earthbound detectors are reduced by up to
about 60%.Comment: 4 pages, 2 figures, 1 tabl

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