207 research outputs found
Polarized Deformed Nuclei Studied via Coincidence Polarized Electron Scattering: The case of 21 Ne
Coincidence reactions of the type \svec{A}(\svec{e},e'N)B involving the
scattering of polarized electrons from deformed polarized targets are discussed
within the context of the plane--wave impulse approximation. A general
expression for the polarized spectral function for transitions leaving the
residual nucleus in discrete states is presented. General properties and
angular symmetries exhibited by the polarization observables are discussed in
detail. Results for unpolarized cross sections as well as for polarization
ratios (asymmetries) are obtained for typical quasi--free kinematics. The
dependences of the polarization observables on the bound neutron momentum,
target polarization orientation, nuclear deformation and value of the momentum
transfer are discussed in detail for various different kinematical
situations.Comment: 37 pages in Plain TeX, MIT-CTP-209
Shapes and beta decay in proton rich Ge, Se, Kr and Sr isotopes
We study ground states and beta decay properties of the proton rich isotope
chains Ge, Se, Kr, and Sr. We use a deformed selfconsistent HF+RPA approach
with density-dependent effective interactions of Skyrme type. We find that most
of the isotopes present two HF minima corresponding to two different shapes. In
addition to static quadrupole moments and other ground state band properties,
we present results for Gamow-Teller strength distributions, as well as for
half-lives and summed strengths. The role of deformation is particularly
emphasized.Comment: 29 pages Revtex, 19 PS figures, to appear in Nucl. Phys.
Nuclear structure calculations for two-neutrino double-beta decay
We study the two-neutrino double-beta decay in 76Ge, 116Cd, 128Te, 130Te, and
150Nd, as well as the two Gamow-Teller branches that connect the double-beta
decay partners with the states in the intermediate nuclei. We use a theoretical
microscopic approach based on a deformed selfconsistent mean field with Skyrme
interactions including pairing and spin-isospin residual forces, which are
treated in a proton-neutron quasiparticle random-phase approximation. We
compare our results for Gamow-Teller strength distributions with experimental
information obtained from charge-exchange reactions. We also compare our
results for the two-neutrino double-beta decay nuclear matrix elements with
those extracted from the measured half-lives. Both single-state and
low-lying-state dominance hypotheses are analyzed theoretically and
experimentally making use of recent data from charge-exchange reactions and
beta decay of the intermediate nuclei.Comment: 11 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1502.0588
Gamow-Teller strength distributions in Fe and Ni stable isotopes
We study Gamow-Teller strength distributions in some selected nuclei of
particular Astrophysical interest within the iron mass region. The theoretical
framework is based on a proton-neutron Quasiparticle Random Phase Approximation
built on a deformed selfconsistent mean field basis obtained from two-body
density-dependent Skyrme forces. We compare our results to available
experimental information obtained from (n,p) and (p,n) charge exchange
reactions.Comment: 11 pages, 3 figure
Warm dark matter sterile neutrinos in electron capture and beta decay spectra
We briefly review the motivation to search for sterile neutrinos in the keV
mass scale, as dark matter candidates, and the prospects to find them in beta
decay or electron capture spectra, with a global perspective. We describe the
fundamentals of the neutrino flavor-mass eigenstate mismatch that opens the
possibility of detecting sterile neutrinos in such ordinary nuclear processes.
Results are shown and discussed for the effect of heavy neutrino emission in
electron capture in Holmium 163 and in two isotopes of Lead, 202 and 205, as
well as in the beta decay of Tritium. We study the de-excitation spectrum in
the considered cases of electron capture and the charged lepton spectrum in the
case of Tritium beta decay. For each of these cases, we define ratios of
integrated transition rates over different regions of the spectrum under study,
and give new results that may guide and facilitate the analysis of possible
future measurements, paying particular attention to forbidden transitions in
Lead isotopes.Comment: 13 pages, 4 figures, 2 table
Isospin mixing and Fermi transitions: Selfconsistent deformed mean field calculations and beyond
We study Fermi transitions and isospin mixing in an isotopic chain 70-78 Kr
considering various approximations that use the same Skyrme-Hartree-Fock single
particle basis. We study Coulomb effects as well as the effect of BCS and
quasiparticle random phase approximation (QRPA) correlations. A measure of
isospin mixing in the approximate ground state is defined by means of the
expectation value of the isospin operator squared in N=Z nuclei (which is
generalized to N different from Z nuclei). Starting from strict Hartree-Fock
approach without Coulomb, it is shown that the isospin breaking is negligible,
on the order of a few per thousand for (N-Z)=6, increasing to a few percent
with Coulomb. Pairing correlations induce rather large isospin mixing and Fermi
transitions of the forbidden type (beta- for NZ). The
enhancement produced by BCS correlations is compensated to a large extent by
QRPA correlations induced by isospin conserving residual interactions that tend
to restore isospin symmetry.Comment: 14 pages, 5 figures, to be published in Phys. Rev.
The Spectral Function for Finite Nuclei in the Local Density Approximation
The spectral function for finite nuclei is computed within the framework of
the Local Density Approximation, starting from nuclear matter spectral
functions obtained with a realistic nucleon-nucleon interaction. The spectral
function is decomposed into a single-particle part and a ''correlated'' part;
the latter is treated in the local density approximation.
As an application momentum distributions, quasi-particle strengths and
overlap functions for valence hole states, and the light-cone momentum
distribution in finite nuclei are computed.Comment: 21 pages + 9 figures available upon request, RevTex, preprint
KVI-108
Theoretical mean field and experimental occupation probabilities in the double beta decay system 76Ge to 76Se
Usual Woods-Saxon single particle levels with BCS pairing are not able to
reproduce the experimental occupation probabilities of the proton and neutron
levels 1p_{3/2}, 1p_{1/2}, 0f_{5/2}, 0g_{9/2} in the double-beta decay system
76Ge to 76Se. Shifting down the 0g_{9/2} level by hand can explain the data but
it is not satisfactory. Here it is shown that a selfconsistent Hartree-Fock+BCS
approach with experimental deformations for 76Ge and 76Se may decisively
improve the agreement with the recent data on occupation probabilities by
Schiffer et al. and Kay et al. Best agreement with available data on 76Ge and
76Se, as well as on neighbor isotopes, is obtained when the spin-orbit strength
for neutrons is allowed to be larger than that for protons. The two-neutrino
double-beta decay matrix element is also shown to agree with data.Comment: 10 pages, 6 figure
Ground-state properties and symmetry energy of neutron-rich and neutron-deficient Mg isotopes
A comprehensive study of various ground-state properties of neutron-rich and
neutron-deficient Mg isotopes with =20-36 is performed in the framework of
the self-consistent deformed Skyrme-Hartree-Fock plus BCS method. The
correlation between the skin thickness and the characteristics related with the
density dependence of the nuclear symmetry energy is investigated for this
isotopic chain following the theoretical approach based on the coherent density
fluctuation model and using the Brueckner energy-density functional. The
results of the calculations show that the behavior of the nuclear charge radii
and the nuclear symmetry energy in the Mg isotopic chain is closely related to
the nuclear deformation. We also study, within our theoretical scheme, the
emergence of an "island of inversion" at neutron-rich Mg nucleus, that
was recently proposed from the analyses of spectroscopic measurements of
Mg low-lying energy spectrum and the charge rms radii of all magnesium
isotopes in the shell.Comment: 13 pages, 13 figures, to be published in Physical Review
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