349 research outputs found
Effect of deformation on two-neutrino double beta decay matrix elements
We study the effect of deformation on the two-neutrino double beta decay for
ground state to ground state transitions in all the nuclei whose half-lives
have been measured. Our theoretical framework is a deformed QRPA based in
Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same
time the main characteristics of the two single beta branches, as well as the
double beta matrix elements. We find a suppression of the double beta matrix
element with respect to the spherical case when the parent and daughter nuclei
have different deformations
Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes
We study Gamow-Teller strength distributions in the neutron-deficient even
isotopes (184-194)Pb in a search for signatures of deformation. The microscopic
formalism used is based on a deformed quasiparticle random phase approximation
(QRPA) approach, which involves a self-consistent quasiparticle deformed Skyrme
Hartree-Fock (HF) basis and residual spin-isospin forces in both the
particle-hole and particle-particle channels. By analyzing the sensitivity of
the Gamow-Teller strength distributions to the various ingredients in the
formalism, we conclude that the beta-decay of these isotopes could be a useful
tool to look for fingerprints of nuclear deformation.Comment: 20 pages, 11 figures. To be published in Physical Review
Gamow-Teller strength distributions in Xe isotopes
The energy distributions of the Gamow-Teller strength are studied for
even-even Xe isotopes with mass numbers from 124 to 142. A self-consistent
microscopic formalism is used to generate the single particle basis, using a
deformed Skyrme Hartree-Fock mean field with pairing correlations in BCS
approximation. The Gamow-Teller transitions are obtained within a quasiparticle
random phase approximation (QRPA) approach using a residual spin-isospin
interaction in the particle-hole and particle-particle channels. We then
discuss the pairing BCS treatment and the determination of the ph and pp
residual interaction coupling constants. We study the GT+ and GT- strength
distributions for the equilibrium nuclear shapes, which are an essential
information for studies of charge-exchange reactions and double-beta processes
involving these isotopes.Comment: 15 pages, 5 figures. To appear in Phys Rev
beta-decay in neutron-deficient Hg, Pb, and Po isotopes
The effect of nuclear deformation on the energy distributions of the
Gamow-Teller strength is studied in neutron-deficient Hg, Pb, and Po even
isotopes. The theoretical framework is based on a self-consistent deformed
Skyrme Hartree-Fock mean field with pairing correlations between like nucleons
in BCS approximation and residual spin-isospin interactions treated in the
proton-neutron quasiparticle random phase approximation. After a systematic
study of the Gamow-Teller strength distributions in the low excitation energy
region, relevant for beta-decay, we have identified the best candidates to look
for deformation signatures in their beta-decay patterns. beta+ half-lives and
total Gamow-Teller strengths B(GT+) and B(GT-) are analyzed as well.Comment: 18 pages, 7 figures, to appear in Phys. Rev.
Half-lives of rp-process waiting point nuclei
We give results of microscopic calculations for the half-lives of various proton-rich nuclei in the mass region A=60-90, which are involved in the astrophysical rp-process, and which are needed as input parameters of numerical simulations in Nuclear Astrophysics. The microscopic formalism consists of a deformed QRPA approach that involves a selfconsistent quasiparticle deformed Skyrme Hartree-Fock basis and residual spin-isospin separable forces in both the particle-hole and particleparticle channels. The strength of the particle-hole residual interaction is chosen to be consistent with the Skyrme effective force and mean field basis, while that of the particle-particle is globally fixed to κ = 0.07 MeV after a judicious choice from comparison to experimental half-lives. We study and discuss the sensitivity of the half-lives to deformation and residual interactions
A deformed QRPA formalism for single and two-neutrino double beta decay
We use a deformed QRPA formalism to describe simultaneously the energy
distributions of the single beta Gamow-Teller strength and the two-neutrino
double beta decay matrix elements. Calculations are performed in a series of
double beta decay partners with A = 48, 76, 82, 96, 100, 116, 128, 130, 136 and
150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock
mean fields. The formalism includes a quasiparticle deformed basis and residual
spin-isospin forces in the particle-hole and particle-particle channels. We
discuss the sensitivity of the parent and daughter Gamow-Teller strength
distributions in single beta decay, as well as the sensitivity of the double
beta decay matrix elements to the deformed mean field and to the residual
interactions. Nuclear deformation is found to be a mechanism of suppression of
the two-neutrino double beta decay. The double beta decay matrix elements are
found to have maximum values for about equal deformations of parent and
daughter nuclei. They decrease rapidly when differences in deformations
increase. We remark the importance of a proper simultaneous description of both
double beta decay and single Gamow-Teller strength distributions. Finally, we
conclude that for further progress in the field it would be useful to improve
and complete the experimental information on the studied Gamow-Teller strengths
and nuclear deformations.Comment: 33 pages, 19 figures. To be published in Phys. Rev.
Relativistic description of 3He(e,e'p)2H
The Relativistic Distorted-Wave Impulse Approximation is used to describe the
He()H process. We describe the He nucleus within the
adiabatic hyperspherical expansion method with realistic nucleon-nucleon
interactions. The overlap between the He and the deuteron wave functions
can be accurately computed from a three-body calculation. The nucleons are
described by solutions of the Dirac equation with scalar and vector (S-V)
potentials. The wave function of the outgoing proton is obtained by solving the
Dirac equation with a S-V optical potential fitted to elastic proton scattering
data on the residual nucleus. Within this theoretical framework, we compute the
cross section of the reaction and other observables like the
transverse-longitudinal asymmetry, and compare them with the available
experimental data measured at JLab.Comment: 4 pages, 3 figures. Proceedings of the 21st European Few Body
Conference held in Salamanca (Spain) in August-September 201
Half-lives of rp-process waiting point nuclei
We give results of microscopic calculations for the half-lives of various
proton-rich nuclei in the mass region A=60-90, which are involved in the
astrophysical rp-process, and which are needed as input parameters of numerical
simulations in Nuclear Astrophysics. The microscopic formalism consists of a
deformed QRPA approach that involves a selfconsistent quasiparticle deformed
Skyrme Hartree-Fock basis and residual spin-isospin separable forces in both
the particle-hole and particle-particle channels. The strength of the
particle-hole residual interaction is chosen to be consistent with the Skyrme
effective force and mean field basis, while that of the particle-particle is
globally fixed to 0.07 MeV after a judicious choice from comparison to
experimental half-lives. We study and discuss the sensitivity of the half-lives
to deformation and residual interactions.Comment: 8 pages, 4 figures, to be published in Eur. Phys. J.
Nuclear isospin mixing and elastic parity-violating electron scattering
The influence of nuclear isospin mixing on parity-violating elastic electron
scattering is studied for the even-even, N=Z nuclei 12C, 24Mg, 28Si, and 32S.
Their ground-state wave functions have been obtained using a self-consistent
axially-symmetric mean-field approximation with density-dependent effective
two-body Skyrme interactions. Some differences from previous shell-model
calculations appear for the isovector Coulomb form factors which play a role in
determining the parity-violating asymmetry. To gain an understanding of how
these differences arise, the results have been expanded in a spherical harmonic
oscillator basis. Results are obtained not only within the plane-wave Born
approximation, but also using the distorted-wave Born approximation for
comparison with potential future experimental studies of parity-violating
electron scattering. To this end, for each nucleus the focus is placed on
kinematic ranges where the signal (isospin-mixing effects on the
parity-violating asymmetry) and the experimental figure-of-merit are maximized.
Strangeness contributions to the asymmetry are also briefly discussed, since
they and the isospin mixing contributions may play comparable roles for the
nuclei being studied at the low momentum transfers of interest in the present
work.Comment: 25 pages, 9 figure
Single and low-lying states dominance in two-neutrino double-beta decay
A theoretical analysis of the single-state dominance hypothesis for the
two-neutrino double-beta decay rates is performed on the examples of the
double-beta decays of 100Mo, 116Cd, and 128Te. We also test the validity of an
extended low-lying-state dominance that takes into account the contributions of
the low-lying excited states in the intermediate nucleus to the double-beta
decay rates. This study has been accomplished for all the double-beta emitters
for which we have experimental information on their half-lives. The theoretical
framework is a proton-neutron quasiparticle random-phase approximation based on
a deformed Skyrme Hartree-Fock mean field with pairing correlations. Our
calculations indicate that there are not clear evidences for single- or
low-lying-state dominance in the two-neutrino double-beta decay. Finally, we
investigate the single electron energy distributions of the outgoing electrons
in the double-beta decay processes with an exact treatment of the energy
denominators, which could help to a more comprehensive analysis of NEMO-3 data.Comment: 19 pages, 6 figure
- …