463 research outputs found
Ground--state energies and widths of He and Li
We extract energies and widths of the ground states of He and Li from
recent single--level R--matrix fits to the spectra of the H)He and the He)Li reactions. The widths
obtained differ significantly from the formal R--matrix values but they are
close to those measured as full widths at half maxima of the spectra in various
experiments. The energies are somewhat lower than those given by usual
estimates of the peak positions. The extracted values are close to the
S--matrix poles calculated previously from the multi--term analyses of the
N-He elastic scattering data.Comment: 3 pages, no figures, uses revtex.sty, accepted for publication in
PRC, uuencoded postscript and tex-files available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/fwidth.u
E2 properties of nuclei far from stability and the proton-halo problem of 8B
E2 properties of A=6--10 nuclei, including those of nuclei far from
stability, are studied by a shell-model calculation which
includes E2 core-polarization effects explicitly. The quadrupole moments and
the E2 transition strengths in A=6--10 nuclei are described quite well by the
present calculation. This result indicates that the relatively large value of
the quadrupole moment of B can be understood without introducing the
proton-halo in B. An interesting effect of the
core-polarization is found for effective charges used in the
shell model; although isoscalar effective-charges are almost constant as a
function of nucleus, appreciable variations are needed for isovector
effective-charges which play important roles in nuclei with high
isospin-values.Comment: (LaTeX, 23 pages
Properties of Be and C deduced from the folding--potential model
The -- differential cross sections are analyzed in the
optical model using a double--folded potential. With the knowledge of this
potential bound and resonance--state properties of --cluster states in
Be and C as well as astrophysical S--factors of
He(,)Be and Be(,)C are
calculated. --widths and B(E2)--values are deduced.Comment: 2 pages LaTeX, 2 figures can be obtained from the author
Isospin Effects in Nuclear Multifragmentation
We develop an improved Statistical Multifragmentation Model that provides the
capability to calculate calorimetric and isotopic observables with precision.
With this new model we examine the influence of nuclear isospin on the fragment
elemental and isotopic distributions. We show that the proposed improvements on
the model are essential for studying isospin effects in nuclear
multifragmentation. In particular, these calculations show that accurate
comparisons to experimental data require that the nuclear masses, free energies
and secondary decay must be handled with higher precision than many current
models accord.Comment: 46 pages, 16 figure
Nuclear halo and its scaling laws
We have proposed a procedure to extract the probability for valence particle
being out of the binding potential from the measured nuclear asymptotic
normalization coefficients. With this procedure, available data regarding the
nuclear halo candidates are systematically analyzed and a number of halo nuclei
are confirmed. Based on these results we have got a much relaxed condition for
nuclear halo occurrence. Furthermore, we have presented the scaling laws for
the dimensionless quantity of nuclear halo in terms of the
analytical expressions of the expectation value for the operator in a
finite square-well potential.Comment: 14 pages, 3 figure
An Attempt to Study T=2 States in 16-N
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Alpha-particle condensation in 16O via a full four-body OCM calculation
In order to explore the 4 \alpha-particle condensate state in 16O, we solve a
full four-body equation of motion based on the 4 \alpha OCM (Orthogonality
Condition Model) in a large 4 \alpha model space spanned by Gaussian basis
functions. A full spectrum up to the 0_6^+ state is reproduced consistently
with the lowest six 0^+ states of the experimental spectrum. The 0^+_6 state is
obtained at about 2 MeV above the 4 \alpha breakup threshold and has a dilute
density structure, with a radius of about 5 fm. The state has an appreciably
large \alpha condensate fraction of 61 %, and a large component of
\alpha+12C(0_2^+) configuration, both features being reliable evidence for this
state to be of 4 \alpha condensate nature.Comment: 4 pages, 3 figures and 1 tabl
Astrophysical Reaction Rates for B(p,)Be and B(p,)Be From a Direct Model
The reactions B(p,)Be and B(p,)Be
are studied at thermonuclear energies using DWBA calculations. For both
reactions, transitions to the ground states and first excited states are
investigated. In the case of B(p,)Be, a resonance at
keV can be consistently described in the potential model, thereby
allowing the extension of the astrophysical -factor data to very low
energies. Strong interference with a resonance at about keV
require a Breit-Wigner description of that resonance and the introduction of an
interference term for the reaction B(p,)Be. Two
isospin resonances (at keV and keV)
observed in the B+p reactions necessitate Breit-Wigner resonance and
interference terms to fit the data of the B(p,)Be
reaction. -factors and thermonuclear reaction rates are given for each
reaction. The present calculation is the first consistent parametrization for
the transition to the ground states and first excited states at low energies.Comment: 27 pages, 5 Postscript figures, uses RevTex and aps.sty; preprint
also available at http://quasar.physik.unibas.ch/ Phys. Rev. C, in pres
Alpha cluster condensation in 12C and 16O
A new -cluster wave function is proposed which is of the
-particle condensate type. Applications to C and O show
that states of low density close to the 3 resp. 4 -particle threshold
in both nuclei are possibly of this kind. It is conjectured that all
self-conjugate 4 nuclei may show similar features.Comment: 4 pages, 2 tables, 2 figure
Reaction rates for Neutron Capture Reactions to C-, N- and O-isotopes to the neutron rich side of stability
The reaction rates of neutron capture reactions on light nuclei are important
for reliably simulating nucleosynthesis in a variety of stellar scenarios.
Neutron capture reaction rates on neutron-rich C-, N-, and O-isotopes are
calculated in the framework of a hybrid compound and direct capture model. The
results are tabulated and compared with the results of previous calculations as
well as with experimental results.Comment: 33 pages (uses revtex) and 9 postscript figures, accepted for
publication in Phys. Rev.
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