465 research outputs found
Nuclear uncertainties in the NeNa-MgAl cycles and production of 22Na and 26Al during nova outbursts
Classical novae eject significant amounts of nuclear processed material into
the interstellar medium. Among the isotopes synthesized during such explosions,
two radioactive nuclei deserve a particular attention: 22Na and 26Al. In this
paper, we investigate the nuclear paths leading to 22Na and 26Al production
during nova outbursts by means of an implicit, hydrodynamic code that follows
the course of the thermonuclear runaway from the onset of accretion up to the
ejection stage. New evolutionary sequences of ONe novae have been computed,
using updated nuclear reaction rates relevant to 22Na and 26Al production.
Special attention is focused on the role played by nuclear uncertainties within
the NeNa and MgAl cycles in the synthesis of such radioactive species. From the
series of hydrodynamic models, which assume upper, recommended or lower
estimates of the reaction rates, we derive limits on the production of both
22Na and 26Al. We outline a list of nuclear reactions which deserve new
experimental investigations in order to reduce the wide dispersion introduced
by nuclear uncertainties in the 22Na and 26Al yields.Comment: 46 pages, 4 figures. Accepted for publication in The Astrophysical
Journa
Thermonuclear Reaction Rate of 23Mg(p,gamma)24$Al
Updated stellar rates for the reaction 23Mg(p,gamma)24Al are calculated by
using all available experimental information on 24Al excitation energies.
Proton and gamma-ray partial widths for astrophysically important resonances
are derived from shell model calculations. Correspondences of experimentally
observed 24Al levels with shell model states are based on application of the
isobaric multiplet mass equation. Our new rates suggest that the
23Mg(p,gamma)24Al reaction influences the nucleosynthesis in the mass A>20
region during thermonuclear runaways on massive white dwarfs.Comment: 13 pages (uses Revtex) including 3 postscript figures (uses
epsfig.sty), accepted for publication in Phys. Rev.
Isobaric multiplet yrast energies and isospin non-conserving forces
The isovector and isotensor energy differences between yrast states of
isobaric multiplets in the lower half of the region are quantitatively
reproduced in a shell model context. The isospin non-conserving nuclear
interactions are found to be at least as important as the Coulomb potential.
Their isovector and isotensor channels are dominated by J=2 and J=0 pairing
terms, respectively. The results are sensitive to the radii of the states,
whose evolution along the yrast band can be accurately followed.Comment: 4 pages, 4 figures. Superseeds second part of nucl-th/010404
Three-body monopole corrections to the realistic interactions
It is shown that a very simple three-body monopole term can solve practically
all the spectroscopic problems--in the , and shells--that were
hitherto assumed to need drastic revisions of the realistic potentials.Comment: 4 pages, 5figure
Up-Down Quark Mass Difference Effect in Nuclear Many-Body Systems
A charge-symmetry-breaking nucleon-nucleon force due to the up-down quark
mass difference is evaluated in the quark cluster model. It is applied to the
shell-model calculation for the isovector mass shifts of isospin multiplets and
the isospin-mixing matrix elements in 1s0d-shell nuclei. We find that the
contribution of the quark mass difference effect is large and agrees with
experiment. This contribution may explain the Okamoto-Nolen-Schiffer anomaly,
alternatively to the meson-mixing contribution, which is recently predicted to
be reduced by the large off-shell correction
Direct neutron capture of 48Ca at kT = 52 keV
The neutron capture cross section of 48Ca was measured relative to the known
gold cross section at kT = 52 keV using the fast cyclic activation technique.
The experiment was performed at the Van-de-Graaff accelerator, Universitaet
Tuebingen. The new experimental result is in good agreement with a calculation
using the direct capture model. The 1/v behaviour of the capture cross section
at thermonuclear energies is confirmed, and the adopted reaction rate which is
based on several previous experimental investigations remains unchanged.Comment: 9 pages (uses Revtex), 2 postscript figures, accepted for publication
as Brief Report in Phys. Rev.
Thermonuclear reaction rate of 23 Mg ( p , Îł ) 24 Al
Updated stellar rates for the reaction 23Mg(p,g )24Al are calculated by using all available experimental information on 24Al excitation energies. Proton and g -ray partial widths for astrophysically important resonances are derived from shell-model calculations. Correspondences of experimentally observed 24Al levels with shell-model states are based on application of the isobaric multiplet mass equation. Our new rates suggest that the 23Mg(p,g )24Al reaction influences the nucleosynthesis in the mass A.20 region during thermonuclear runaways on massive white dwarfs
On the Strength of Spin-Isospin Transitions in A=28 Nuclei
The relations between the strengths of spin-isospin transition operators
extracted from direct nuclear reactions, magnetic scattering of electrons and
processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur
A Global Potential Analysis of the O+Si Reaction Using a New Type of Coupling Potential
A new approach has been used to explain the experimental data for the
O+Si system over a wide energy range in the laboratory system
from 29.0 to 142.5 MeV. A number of serious problems has continued to plague
the study of this system for a couple of decades. The explanation of anomalous
large angle scattering data; the reproduction of the oscillatory structure near
the Coulomb barrier; the out-of-phase problem between theoretical predictions
and experimental data; the consistent description of angular distributions
together with excitation functions data are just some of these problems. These
are long standing problems that have persisted over the years and do represent
a challenge calling for a consistent framework to resolve these difficulties
within a unified approach. Traditional frameworks have failed to describe these
phenomena within a single model and have so far only offered different
approaches where these difficulties are investigated separately from one
another. The present work offers a plausible framework where all these
difficulties are investigated and answered. Not only it improves the
simultaneous fits to the data of these diverse observables, achieving this
within a unified approach over a wide energy range, but it departs for its
coupling potential from the standard formulation. This new feature is shown to
improve consistently the agreement with the experimental data and has made
major improvement on all the previous coupled-channels calculations for this
system.Comment: 21 pages with 12 figure
Beta-decay properties of Si and P
The -decay properties of the neutron-deficient nuclei Si and
P have been investigated at the GANIL/LISE3 facility by means of
charged-particle and -ray spectroscopy. The decay schemes obtained and
the Gamow-Teller strength distributions are compared to shell-model
calculations based on the USD interaction. B(GT) values derived from the
absolute measurement of the -decay branching ratios give rise to a
quenching factor of the Gamow-Teller strength of 0.6. A precise half-life of
43.7 (6) ms was determined for P, the - (2)p decay mode of which
is described
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