202 research outputs found
SU(3) symmetry breaking in lower fp-shell nuclei
Results of shell-model calculations for lower fp-shell nuclei show that SU(3)
symmetry breaking in this region is driven by the single-particle spin-orbit
splitting. However, even though states of the yrast band exhibit SU(3) symmetry
breaking, the results also show that the yrast band B(E2) values are
insensitive to this fragmentation of the SU(3) symmetry; specifically, the
quadrupole collectivity as measured by B(E2) transition strengths between low
lying members of the yrast band remain high even though SU(3) appears to be
broken. Results for and using the Kuo-Brown-3
two-body interaction are given to illustrate these observations.Comment: Updated to the published versio
QED Calculation of E1M1 and E1E2 Transition Probabilities in One-Electron Ions with Arbitrary Nuclear Charge
The quantum electrodynamical theory of the two-photon transitions in
hydrogenlike ions is presented. The emission probability for 2s1/2 -> 2E1+1s1/2
transitions is calculated and compared to the results of the previous
calculations. The emission probabilities 2p12 -> E1E2+1s1/2 and 2p1/2 ->
E1M1+1s1/2 are also calculated for the nuclear charge Z values 1-100. This is
the first calculation of the two latter probabilities. The results are given in
two different gauges.Comment: 14 pages, 4 tables, 1 figur
Majoron emitting neutrinoless double beta decay in the electroweak chiral gauge extensions
Fundamental mechanisms for Majoron emitting neutrinoless double beta decay in
SU(3)_C x G_W x U(1) models, for electroweak flavor chiral extensions, G_W =
SU(3)_L and SU(4)_L are pointed out. Both kinds of known Majoron emitting
processes, charged Majoron emitting where the massless Nambu-Goldstone boson
itself carries lepton charge, , and the ordinary Majoron emitting where
the boson has a small mass are found possible. PACS numbers: 11.15.Ex,
12.60.Fr, 14.80.CpComment: 18 pages, Revtex, 3 Postscript figures. To be published in
Phys.Rev.D(1 May 1998
Double Beta Decay: Historical Review of 75 Years of Research
Main achievements during 75 years of research on double beta decay have been
reviewed. The existing experimental data have been presented and the
capabilities of the next-generation detectors have been demonstrated.Comment: 25 pages, typos adde
Constraints on Lorentz violation from clock-comparison experiments
Constraints from clock-comparison experiments on violations of Lorentz and
CPT symmetry are investigated in the context of a general Lorentz-violating
extension of the standard model. The experimental signals are shown to depend
on the atomic and ionic species used as clocks. Certain experiments usually
regarded as establishing comparable bounds are in this context sensitive to
different types of Lorentz violation. Some considerations relevant to possible
future measurements are presented. All these experiments are potentially
sensitive to Lorentz-violating physics at the Planck scale.Comment: accepted for publication in Physical Review D; scheduled for issue of
December 1, 199
Recent advances in neutrinoless double beta decay search
Even after the discovery of neutrino flavour oscillations, based on data from
atmospheric, solar, reactor, and accelerator experiments, many characteristics
of the neutrino remain unknown. Only the neutrino square-mass differences and
the mixing angle values have been estimated, while the value of each mass
eigenstate still hasn't. Its nature (massive Majorana or Dirac particle) is
still escaping. Neutrinoless double beta decay (-DBD) experimental
discovery could be the ultimate answer to some delicate questions of elementary
particle and nuclear physics. The Majorana description of neutrinos allows the
-DBD process, and consequently either a mass value could be measured or
the existence of physics beyond the standard should be confirmed without any
doubt. As expected, the -DBD measurement is a very difficult field of
application for experimentalists. In this paper, after a short summary of the
latest results in neutrino physics, the experimental status, the R&D projects,
and perspectives in -DBD sector are reviewed.Comment: 36 pages, 7 figures, To be publish in Czech Journal of Physic
Shell structure of superheavy nuclei in self-consistent mean-field models
We study the extrapolation of nuclear shell structure to the region of
superheavy nuclei in self-consistent mean-field models -- the
Skyrme-Hartree-Fock approach and the relativistic mean-field model -- using a
large number of parameterizations. Results obtained with the Folded-Yukawa
potential are shown for comparison. We focus on differences in the isospin
dependence of the spin-orbit interaction and the effective mass between the
models and their influence on single-particle spectra. While all relativistic
models give a reasonable description of spin-orbit splittings, all
non-relativistic models show a wrong trend with mass number. The spin-orbit
splitting of heavy nuclei might be overestimated by 40%-80%. Spherical
doubly-magic superheavy nuclei are found at (Z=114,N=184), (Z=120,N=172) or
(Z=126,N=184) depending on the parameterization. The Z=114 proton shell
closure, which is related to a large spin-orbit splitting of proton 2f states,
is predicted only by forces which by far overestimate the proton spin-orbit
splitting in Pb208. The Z=120 and N=172 shell closures predicted by the
relativistic models and some Skyrme interactions are found to be related to a
central depression of the nuclear density distribution. This effect cannot
appear in macroscopic-microscopic models which have a limited freedom for the
density distribution only. In summary, our findings give a strong argument for
(Z=120,N=172) to be the next spherical doubly-magic superheavy nucleus.Comment: 22 pages REVTeX, 16 eps figures, accepted for publication in Phys.
Rev.
Evidence for a spin-aligned neutron-proton paired phase from the level structure of Pd
The general phenomenon of shell structure in atomic nuclei has been
understood since the pioneering work of Goeppert-Mayer, Haxel, Jensen and
Suess.They realized that the experimental evidence for nuclear magic numbers
could be explained by introducing a strong spin-orbit interaction in the
nuclear shell model potential. However, our detailed knowledge of nuclear
forces and the mechanisms governing the structure of nuclei, in particular far
from stability, is still incomplete. In nuclei with equal neutron and proton
numbers (), the unique nature of the atomic nucleus as an object
composed of two distinct types of fermions can be expressed as enhanced
correlations arising between neutrons and protons occupying orbitals with the
same quantum numbers. Such correlations have been predicted to favor a new type
of nuclear superfluidity; isoscalar neutron-proton pairing, in addition to
normal isovector pairing (see Fig. 1). Despite many experimental efforts these
predictions have not been confirmed. Here, we report on the first observation
of excited states in nucleus Pd. Gamma rays emitted
following the Ni(Ar,2)Pd fusion-evaporation reaction
were identified using a combination of state-of-the-art high-resolution
{\gamma}-ray, charged-particle and neutron detector systems. Our results reveal
evidence for a spin-aligned, isoscalar neutron-proton coupling scheme,
different from the previous prediction. We suggest that this coupling scheme
replaces normal superfluidity (characterized by seniority coupling) in the
ground and low-lying excited states of the heaviest N = Z nuclei. The strong
isoscalar neutron- proton correlations in these nuclei are predicted to
have a considerable impact on their level structures, and to influence the
dynamics of the stellar rapid proton capture nucleosynthesis process.Comment: 13 pages, 3 figure
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