139 research outputs found
Large-scale deformed quasiparticle random-phase approximation calculations of the -ray strength function using the Gogny force
Valuable theoretical predictions of nuclear dipole excitations in the whole
chart are of great interest for different nuclear applications, including in
particular nuclear astrophysics. Here we present large-scale calculations of
the -ray strength function obtained in the framework of the
axially-symmetric deformed QRPA based on the finite-range Gogny force. This
approach is applied to even-even nuclei, the strength function for odd nuclei
being derived by interpolation. The convergence with respect to the adopted
number of harmonic oscillator shells and the cut-off energy introduced in the
2-quasiparticle (2-) excitation space is analyzed. The calculations
performed with two different Gogny interactions, namely D1S and D1M, are
compared. A systematic energy shift of the strength is found for D1M
relative to D1S, leading to a lower energy centroid and a smaller
energy-weighted sum rule for D1M. When comparing with experimental
photoabsorption data, the Gogny-QRPA predictions are found to overestimate the
giant dipole energy by typically 2 MeV. Despite the microscopic nature of
our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some
phenomenological corrections need to be included to take into account the
effects beyond the standard 2- QRPA excitations and the coupling between
the single-particle and low-lying collective phonon degrees of freedom. For
this purpose, three prescriptions of folding procedure are considered and
adjusted to reproduce experimental photoabsorption data at best. All of them
are shown to lead to rather similar predictions of the strength, both at
low energies and for exotic neutron-rich nuclei. Predictions of -ray
strength functions and Maxwellian-averaged neutron capture rates for the whole
Sn isotopic chain are also discussed and compared with previous theoretical
calculations
Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields
Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the
spherical Hartree-Fock calculations with the semi-realistic interactions.
Specific ingredients of the effective interaction, particularly the tensor
force, often play a key role in the dependence of the neutron shell
structure. Such examples are found in N=32 and N=40; N=32 becomes magic or
submagic in Ca while its magicity is broken in Ni, and N=40 is
submagic (though not magic) in Ni but not in Ca. Comments are
given on the doubly magic nature of Ni. We point out that the loose
binding can lead to a submagic number N=58 in Ni, assisted by the weak
pair coupling.Comment: 14 pages including 5 figures, to appear in Physical Review C (Rapid
Communication
Giant resonances in exotic spherical nuclei within the RPA approach with the Gogny force
Theoretical results for giant resonances in the three doubly magic exotic
nuclei Ni, Sn and Sn are obtained from Hartree-Fock (HF)
plus Random Phase Approximation (RPA) calculations using the D1S
parametrization of the Gogny two-body effective interaction. Special attention
is paid to full consistency between the HF field and the RPA particle-hole
residual interaction. The results for the exotic nuclei, on average, appear
similar to those of stable ones, especially for quadrupole and octupole states.
More exotic systems have to be studied in order to confirm such a trend. The
low energy of the monopole resonance in Ni suggests that the compression
modulus in this neutron rich nucleus is lower than the one of stable ones.Comment: 16 pages, 10 figure
Role of deformation on giant resonances within the QRPA approach and the Gogny force
Fully consistent axially-symmetric-deformed Quasi-particle Random Phase
Approximation (QRPA) calculations have been performed, in which the same Gogny
D1S effective force has been used for both the Hartree-Fock-Bogolyubov mean
field and the QRPA approaches. Giant resonances calculated in deformed
Si and Mg nuclei as well as in the spherical Si and
Mg isotopes are presented. Theoretical results for isovector-dipole and
isoscalar monopole, quadrupole, and octupole responses are presented and the
impact of the intrinsic nuclear deformation is discussed.Comment: 12 pages, 6 figures and 4 tables, accepted in PR
Quadrupole moment of the 6− isomeric state in 66Cu: Interplay between different nuclear deformation driving forces
AbstractWe have measured the spectroscopic quadrupole moment of the 6− isomeric state in 66Cu to be |Qs|=18.6(12) efm2. This state results from a weak coupling of the πp3/2 and the νg9/2 orbitals, which lead to sizable deformation at oblate and prolate shapes, correspondingly, in the 68Ni region. The interplay between these two different deformation-driving orbitals is observed at N=37 for the 6− state resulting in a most probable oblate shape
Unexpected high-energy γ emission from decaying exotic nuclei
Abstract The N = 52 Ga 83 β decay was studied at ALTO. The radioactive 83Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ-ray emission following β decay. While β-delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ-ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β-decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei
Photoneutron cross sections for samarium isotopes: Toward a unified understanding of (
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