101 research outputs found
Neutrino-Nucleus Reactions and Muon Capture in 12C
The neutrino-nucleus cross section and the muon capture rate are discussed
within a simple formalism which facilitates the nuclear structure calculations.
The corresponding formulae only depend on four types of nuclear matrix
elements, which are currently used in the nuclear beta decay. We have also
considered the non-locality effects arising from the velocity-dependent terms
in the hadronic current. We show that for both observables in 12C the higher
order relativistic corrections are of the order of ~5 only, and therefore do
not play a significant role. As nuclear model framework we use the projected
QRPA (PQRPA) and show that the number projection plays a crucial role in
removing the degeneracy between the proton-neutron two quasiparticle states at
the level of the mean field. Comparison is done with both the experimental data
and the previous shell model calculations. Possible consequences of the present
study on the determination of the neutrino oscillation
probability are briefly addressed.Comment: 29 pages, 6 figures, Revtex4. Several changes were made to the
previous manuscript, the results and final conclusions remain unalterable. It
has been accepted for publication as a Regular Article in Physical Review
Time Reversal Invariance Violating and Parity Conserving effects in Neutron Deuteron Scattering
Time reversal invariance violating parity conserving effects for low energy
elastic neutron deuteron scattering are calculated for meson exchange and
EFT-type of potentials in a Distorted Wave Born Approximation, using realistic
hadronic wave functions, obtained by solving three-body Faddeev equations in
configuration space.Comment: There was a technical mistake in calculations due to singular
behavior of Yukawa functions at short range. We corrected the integration
algorithm. There were some typos which are corrected. arXiv admin note: text
overlap with arXiv:1104.305
Isoscalar g Factors of Even-Even and Odd-Odd Nuclei
We consider T=0 states in even-even and odd-odd N=Z nuclei. The g factors
that emerge are isoscalar. We find that the single j shell model gives simple
expressions for these g factors which for even-even nuclei are suprisingly
close to the collective values for K=0 bands. The g factors of many 2+ in
even-even nuclei and 1+ and 3+ states in odd-odd nuclei have g factors close to
0.5
A new online database of nuclear electromagnetic moments
Nuclear electromagnetic (EM) moments, i.e., the magnetic dipole and the electric quadrupole moments, provide important information of nuclear structure. As in other types of experimental data available to the community, measurements of nuclear EM moments have been organized systematically in compilations since the dawn of nuclear science. However, the wealth of recent moments measurements with radioactive beams, as well as earlier existing measurements, lack an online, easy-to-access, systematically organized presence to disseminate information to researchers. In addition, available printed compilations suffer a rather long life cycle, being left behind experimental measurements published in journals or elsewhere. A new, online database (http://magneticmoments.info) focusing on nuclear EM moments has been recently developed to disseminate experimental data to the community. The database includes non–evaluated experimental data of nuclear EM moments, giving strong emphasis on frequent updates (life cycle is 3 months) and direct connection to the sources via DOI and NSR hyperlinks. It has been recently integrated in IAEA LiveChart [1], but can also be found as a standalone webapp [2]. A detailed review of the database features, as well as plans for further development and expansion in the near future is discussed
Isospin-mixing corrections for fp-shell Fermi transitions
Isospin-mixing corrections for superallowed Fermi transitions in {\it
fp}-shell nuclei are computed within the framework of the shell model. The
study includes three nuclei that are part of the set of nine accurately
measured transitions as well as five cases that are expected to be measured in
the future at radioactive-beam facilities. We also include some new
calculations for C. With the isospin-mixing corrections applied to the
nine accurately measured values, the conserved-vector-current hypothesis
and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are
tested.Comment: 13 pages plus five tables. revtex macro
Magnetic moments of Mg in time-odd relativistic mean field approach
The configuration-fixed deformation constrained relativistic mean field
approach with time-odd component has been applied to investigate the
ground-state properties of Mg with effective interaction PK1. The ground
state of Mg has been found to be prolate deformed, , with
the odd neutron in orbital and the energy -251.85 MeV which is close
to the data -252.06 MeV. The magnetic moment is
obtained with the effective electromagnetic current which well reproduces the
data self-consistently without introducing any
parameter. The energy splittings of time reversal conjugate states, the neutron
current, the energy contribution from the nuclear magnetic potential, and the
effect of core polarization are discussed in detail.Comment: 13 pages, 4 figure
Large-basis shell-model calculation of 10C->10B Fermi matrix element
We use a shell-model calculation with a two-body effective
interaction derived microscopically from the Reid93 potential to calculate the
isospin-mixing correction for the 10C->10B superallowed Fermi transition. The
effective interaction takes into account the Coulomb potential as well as the
charge dependence of T=1 partial waves. Our results suggest the isospin- mixing
correction , which is compatible with previous
calculations. The correction obtained in those calculations, performed in a
space, was dominated by deviation from unity of the radial
overlap between the converted proton and the corresponding neutron. In the
present calculation this effect is accommodated by the large model space. The
obtained correction is about a factor of four too small to obtain
unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental
data.Comment: 14 pages. REVTEX. 3 PostScript figure
Parity nonconservation effects in the photodesintegration of polarized deuterons
P-odd correlations in the deuteron photodesintegration are considered. The
-meson exchange is not operative in the case of unpolarized deuterons. For
polarized deuterons a P-odd correlation due to the -meson exchange is
about . Short-distance P-odd contributions exceed essentially
than the contribution of the -meson exchange.Comment: 12 pages, Latex, 3 figure
Partially conserved axial current constraints on pion production/absorption within nonrelativistic dynamics
We show the necessity of two-nucleon axial currents and associated pion
emission/ absorption operators for the partial conservation of the axial
current (PCAC) nuclear matrix elements with arbitrary nuclear dynamics
described by a nonrelativistic Schroedinger equation. As examples we construct
such nonrelativistic axial two-body currents in the linear- and heterotic (g_A
= 1.26) sigma models, with an optional isoscalar vector (omega) meson exchange.
The nuclear matrix elements obey PCAC only if the nuclear wave functions used
in the calculation are solutions to the Schroedinger equation with the static
one-meson-exchange potential constructed in the respective (sigma) model. The
same holds true for the nucler pion production amplitude, since it is
proportional to the divergence of the axial current matrix element, by virtue
of PCAC. Thus we found a new consistency condition between the pion
creation/absorption operator and the nuclear Hamiltonian. We present examples
drawn from our models and discuss implications for one-pion-two-nucleon
processes.Comment: 19 pages, 7 figures, submitted to Phys. Rev.
Towards a Statistical Theory of Finite Systems and Compound States: Random Two-Body Interaction Approach
The model of Fermi particles with random two-body interaction is
investigated. This model allows to study the origin and accuracy of statistical
laws in few-body systems, the role of interaction and chaos in thermalization,
Fermi-Dirac distribution for quasi-particles with spreading widths, matrix
elements of external field and enhancement of weak perturbation in chaotic
compound states.Comment: 4 pages in RevTex and 2 Postscript figures; to appear in Phys.Rev.
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