5,969 research outputs found
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
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.
Age determination of the HR8799 planetary system using asteroseismology
Discovery of the first planetary system by direct imaging around HR8799 has
made the age determination of the host star a very important task. This
determination is the key to derive accurate masses of the planets and to study
the dynamical stability of the system. The age of this star has been estimated
using different procedures. In this work we show that some of these procedures
have problems and large uncertainties, and the real age of this star is still
unknown, needing more observational constraints. Therefore, we have developed a
comprehensive modeling of HR8799, and taking advantage of its gamma
Doradus-type pulsations, we have estimated the age of the star using
asteroseismology. The accuracy in the age determination depends on the rotation
velocity of the star, and therefore an accurate value of the inclination angle
is required to solve the problem. Nevertheless, we find that the age estimate
for this star previously published in the literature ([30,160] Myr) is
unlikely, and a more accurate value might be closer to the Gyr. This
determination has deep implications on the value of the mass of the objects
orbiting HR8799. An age around 1 Gyr implies that these objects are
brown dwarfs.Comment: 5 pages, 3 figures, accepted in MNRAS Letter
Effects of husbandry and low-dose lipopolysaccharide challenge on the acute phase response of young pigs
End of project reportIn recent years, concern has grown for the welfare of domesticated animals in different production systems (Appleby and Hughes, 1997). Poor welfare can result in poor performance and productivity. However, the consumers are also requesting more welfare-friendly systems, as reflected by the importance that ‘organic’ and ‘free-range’ products have gained in our markets. Furthermore, there are ethical reasons for safeguarding the welfare of animals in our care. Thus, it is scientists’ task to be able to develop methods and techniques that can help to assess the welfare objectively. Traditionally, welfare assessment relied on the study of behaviour and the measurement of endocrine parameters. Acute phase response mediators and products, such as pro-inflammatory cytokines and acute phase proteins, emerged recently as potential indicators of infection and herd health status (Eckersall, 2000; Petersen et al., 2004). Thus, investigating the effects of husbandry and low-dose lipopolysaccharide (LPS) challenge on the acute phase response of young pigs can give valuable information on the use of these immune parameters as health and welfare indicators in pigs.Teagasc acknowledges the support of National Development Programme Funds (NDP) in the financing of this research projec
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
Nuclear Pairing in the T=0 channel revisited
Recent published data on the isoscalar gap in symmetric nuclear matter using
the Paris force and the corresponding BHF single particle dispersion are
corrected leading to an extremely high proton-neutron gap of
MeV at . Arguments whether this value can be reduced due
to screening effects are discussed. A density dependent delta interaction with
cut off is adjusted so as to approximately reproduce the nuclear matter values
with the Paris force.Comment: 4 pages, 4 figure
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