340 research outputs found
T=0 effective interaction in 14N and 10B
We have calculated the 1+ and 3+, T=0 states in 14N and 10B. In a
neutron-proton RPA model these two nuclei are described by the same set of
equations. We first show that a bare Minnesota interaction leads to too weak
binding in bothnuclei. Furthermore it does not produce a 3+ ground state in 10B
as it should. Including medium effects as an exchange of phonons between the
neutron-proton pair cures the desagreement in 14N but still gives a 1+ ground
state in 10B with the 3+ as an excited state. The same study with a Gogny
effective interaction reproduces nicely the properties of both nuclei: same
agreement in 14N as previously when medium effeccts were introduced but now the
3+ in 10B becomes the ground state. This success suggests that through its
density dependent term the Gogny interaction takes account of the presence of a
three-body force which, in a shell model calculation, has been shown to be
essential to give a 3+ ground state in 10B
Deformation or spherical symmetry in 10Be and the inversion of 1/2- - 1/2+ states in 11Be
For a core plus one neutron system like 11Be we have calculated the energies
of the 1/2- and 1/2+ states assuming a deformation of the core deduced from the
low energy 2+ state properties or taking into account the coupling of the
neutron with this 2+ state interpreted as a spherical one-phonon state. We have
shown that the two derivations yield identical results if the phonon energy is
neglected in the second derivation and close results in the general case
Response Function of Hot Nuclear Matter
We investigate the response function of hot nuclear matter to a small
isovector external field using a simplified Skyrme interaction reproducing the
value of the symmetry energy coefficient.
We consider values of the momentum transfer corresponding to the dipole
oscillation in heavy nuclei. We find that while at zero temperature the
particle hole interaction is almost repulsive enough to have a sharp (zero
sound type) collective oscillation, such is no longer the case at temperatures
of a few MeV. As a result a broadening of the dipole resonance occurs, leading
to its quasi disappearence by the time the temperature reaches 5 MeV. The
sensivity of the temperature evolution of the width when modifying the residual
interaction strength is also examined.Comment: 9 pages, IPNO/TH 94-15, DPT-IPN Orsay. Two figures available under
reques
Radiative proton-antiproton annihilation and isospin mixing in protonium
A detailed analysis of the radiative annihilation is made in the
framework of a two-step formalism, the annihilates into meson
channels containing a vector meson with a subsequent conversion into a photon
via the vector dominance model (VDM). Both steps are derived from the
underlying quark model. First, branching ratios for radiative protonium
annihilation are calculated and compared with data. Then, details of the
isospin interference are studied for different models of the initial protonium
state and also for different kinematical form factors. The isospin interference
is shown to be uniquely connected to the mixing in the
protonium state. Values of the interference terms directly deduced from data
are consistent with theoretical expectations, indicating a dominant
component for the and a sizable component for the
protonium state. The analysis is extended to the
transition, where the large observed branching ratio remains unexplained in the
VDM approach.Comment: 34 pages, RevTeX, 2 figures, to appear in Phys. Rev. C; typos
correcte
Li spectrum from Li fragmentation
A recently developed time dependent model for the excitation of a nucleon
from a bound state to a continuum resonant state in the system n+core is
applied to the study of the population of the low energy continuum of the
unbound Li system obtained from Li fragmentation. Comparison of
the model results to new data from the GSI laboratory suggests that the
reaction mechanism is dominated by final state effects rather than by the
sudden process, but for the population of the l=0 virtual state, in which case
the two mechanisms give almost identical results. There is also, for the first
time, a clear evidence for the population of a d resonance in
Li.Comment: 15 pages, 4 figures, 3 tables. Accepted for publication in
Nucl.Phys.
Particle-particle random phase approximation applied to Beryllium isotopes
This work is dedicated to the study of even-even 8-14 Be isotopes using the
particle-particle Random Phase Approximation that accounts for two-body
correlations in the core nucleus. A better description of energies and
two-particle amplitudes is obtained in comparison with models assuming a
neutron closed-shell (or subshell) core. A Wood-Saxon potential corrected by a
phenomenological particle-vibration coupling term has been used for the
neutron-core interaction and the D1S Gogny force for the neutron-neutron
interaction. Calculated ground state properties as well as excited state ones
are discussed and compared to experimental data. In particular, results suggest
the same 2s_1/2-1p_1/2 shell inversion in 13Be as in 11Be.Comment: to appear in Phys. Rev.
Response function beyond mean field of neutron-rich nuclei
The damping of single-particle and collective motion in exotic isotopes is a
new topic and its study may shed light on basic problems of nuclear dynamics.
For instance, it is known that nuclear structure calculations are not able, as
a rule, to account completely for the empirical single-particle damping. In
this contribution, we present calculations of the single-particle self-energy
in the case of the neutron-rich light nucleus O, by taking proper care
of the continuum, and we show that there are important differences with the
case of nuclei along the valley of stability.Comment: 9 pages, 4 figures. To appear in: Proceedings of the Topical
Conference on Giant Resonances, Varenna, May 11-16, 1997 (Nucl. Phys. A, to
be published
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