1,804 research outputs found
Neutrinoless decay nuclear matrix elements in an isotopic chain
We analyze nuclear matrix elements (NME) of neutrinoless double beta decay
calculated for the Cadmium isotopes. Energy density functional methods
including beyond mean field effects such as symmetry restoration and shape
mixing are used. Strong shell effects are found associated to the underlying
nuclear structure of the initial and final nuclei. Furthermore, we show that
NME for two-neutrino double beta decay evaluated in the closure approximation,
, display a constant proportionality with respect to
the Gamow-Teller part of the neutrinoless NME, . This
opens the possibility of determining the matrix
elements from Gamow-Teller strength functions. Finally, the
interconnected role of deformation, pairing, configuration mixing and shell
effects in the NMEs is discussed
Calculation of nuclear matrix elements in neutrinoless double electron capture
We compute nuclear matrix elements for neutrinoless double electron capture
on Gd, Er and W nuclei. Recent precise mass
measurements for these nuclei have shown a large resonance enhancement factor
that makes them the most promising candidates for observing this decay mode. We
use an advanced energy density functional method which includes beyond
mean-field effects such as symmetry restoration and shape mixing. Our
calculations reproduce experimental charge radii and values predicting
a large deformation for all these nuclei. This fact reduces significantly the
values of the NMEs leading to half-lives larger than years for the
three candidates
Systematic study of infrared energy corrections in truncated oscillator spaces
We study the convergence properties of nuclear binding energies and
two-neutron separation energies obtained with self-consistent mean-field
calculations based on the Hartree-Fock-Bogolyubov (HFB) method with Gogny-type
effective interactions. Owing to lack of convergence in a truncated working
basis, we employ and benchmark one of the recently proposed infrared energy
correction techniques to extrapolate our results to the limit of an infinite
model space. We also discuss its applicability to global calculations of
nuclear masses.Comment: 12 pages, 12 figure
Improved estimate of electron capture rates on nuclei during stellar core collapse
Electron captures on nuclei play an important role in the dynamics of the
collapsing core of a massive star that leads to a supernova explosion. Recent
calculations of these capture rates were based on microscopic models which
account for relevant degrees of freedom. Due to computational restrictions such
calculations were limited to a modest number of nuclei, mainly in the mass
range A=45-110. Recent supernova simulations show that this pool of nuclei,
however, omits the very neutron-rich and heavy nuclei which dominate the
nuclear composition during the last phase of the collapse before neutrino
trapping. Assuming that the composition is given by Nuclear Statistical
Equilibrium we present here electron capture rates for collapse conditions
derived from individual rates for roughly 2700 individual nuclei. For those
nuclei which dominate in the early stage of the collapse, the individual rates
are derived within the framework of microscopic models, while for the nuclei
which dominate at high densities we have derived the rates based on the Random
Phase Approximation with a global parametrization of the single particle
occupation numbers. In addition, we have improved previous rate evaluations by
properly including screening corrections to the reaction rates into account.Comment: 32 pages, 13 figures, 1 table; elsart; to appear in Nuclear Physics
Gamma-Ray Bursts Black hole accretion disks as a site for the vp-process
We study proton rich nucleosynthesis in windlike outflows from gamma-ray
bursts accretion disks with the aim to determine if such outflows are a site of
the vp-process. The efficacy of this vp-process depends on thermodynamic and
hydrodynamic factors. We discuss the importance of the entropy of the material,
the outflow rate, the initial ejection point and accretion rate of the disk. In
some cases the vp-process pushes the nucleosynthesis out to A~100 and produces
light p-nuclei. However, even when these nuclei are not produced, neutrino
induced interactions can significantly alter the abundance pattern and cannot
be neglected.Comment: 9 pages, 16 figures, accepted for publication in Phys. Rev.
Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei
We calculate parity-dependent level densities for the even-even isotopes
58,62,66 Fe and 58 Ni and the odd-A nuclei 59 Ni and 65 Fe using the Shell
Model Monte Carlo method. We perform these calculations in the complete fp-gds
shell-model space using a pairing+quadrupole residual interaction. We find
that, due to pairing of identical nucleons, the low-energy spectrum is
dominated by positive parity states. Although these pairs break at around the
same excitation energy in all nuclei, the energy dependence of the ratio of
negative-to-positive parity level densities depends strongly on the particular
nucleus of interest. We find equilibration of both parities at noticeably lower
excitation energies for the odd-A nuclei 59 Ni and 65 Fe than for the
neighboring even-even nuclei 58 Ni and 66 Fe.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Métodos de fertilización para rendimiento comercial en tres cultivares de ajo (Allium sativum L.)
Garlic (Allium sativum L.) is an important crop for domestic consumption in Peru. However, there is insufficient information available on crop management, particularly on fertiliser application to local cultivars. In order to evaluate the response of three garlic cultivars to three fertilisation methods, an experiment was conducted at the Donoso Experimental Station in Huaral district, a province of Lima. Three garlic cultivars were used as experimental materials: ‘Cincomesino’, ‘Arequipeño 14’ and ‘Margosino’. Three methods of fertilisation were applied as treatments: broadcast application before furrowing (M1), fertilisation in a superficial groove or false furrow (M2), and fertilisation in the lateral furrows, or band application (M3). The experiments were installed in three parcels for each cultivar, with a randomised complete block design for each parcel and four replications. In general, localised fertilisation methods showed the best performance for the broadcast method. Regarding total yield, fertilisation at the sides of the furrow (M3) for ‘Cincomesino’ reached 13.08 t/ha. The highest yield for the ‘Arequipeño 14’ cultivar (12.25 t/ha) was achieved using fertilisation with a surface groove or false furrow (M2). For the ‘Margosino’ cultivar, fertilisation on the sides of the furrow was ideal, and the yield was 10.95 t/ha
Fission Cycling in a Supernova r-process
Recent halo star abundance observations exhibit an important feature of
consequence to the r-process: the presence of a main r-process between the
second and third peaks which is consistent among halo stars. We explore fission
cycling and steady-beta flow as the driving mechanisms behind this feature. The
presence of fission cycling during the r-process can account for
nucleosynthesis yields between the second and third peaks, whereas the presence
of steady-beta flow can account for consistent r-process patterns, robust under
small variations in astrophysical conditions. We employ the neutrino-driven
wind of the core-collapse supernova to examine fission cycling and steady-beta
flow in the r-process. As the traditional neutrino-driven wind model does not
produce the required very neutron-rich conditions for these mechanisms, we
examine changes to the neutrino physics necessary for fission cycling to occur
in the neutrino-driven wind environment, and we explore under what conditions
steady-beta flow is obtained.Comment: 9 pages, 8 figure
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