161 research outputs found
The Quasi-Molecular Stage of Ternary Fission
We developed a three-center phenomenological model,able to explain
qualitatively the recently obtained experimental results concerning the
quasimolecular stage of a light-particle accompanied fission process. It was
derived from the liquid drop model under the assumption that the aligned
configuration, with the emitted particle between the light and heavy fragment,
is reached by increasing continuously the separation distance, while the radii
of the heavy fragment and of the light particle are kept constant. In such a
way,a new minimum of a short-lived molecular state appears in the deformation
energy at a separation distance very close to the touching point. This minimum
allows the existence of a short-lived quasi-molecular state, decaying into the
three final fragments.The influence of the shell effects is discussed. The
half-lives of some quasimolecular states which could be formed in the Be
and C accompanied fission of Cf are roughly estimated to be the
order of 1 ns, and 1 ms, respectively.Comment: 12 pages, 6 epsf, uses ws-p8-50x6-00.cl
Alpha decay half-lives of new superheavy elements
The lifetimes of decays of the recently produced isotopes of the
elements 112, 114, 116 and the element and of some decay products
have been calculated theoretically within the WKB approximation using
microscopic -nucleus interaction potentials. These nuclear potentials
have been obtained by folding the densities of the and the daughter
nuclei with the M3Y effective interaction, supplemented by a zero-range
pseudo-potential for exchange along with the density dependence. Spherical
charge distributions have been used for calculating the Coulomb interaction
potentials. These calculations provide reasonable estimates for the observed
decay lifetimes and thus provide reliable predictions for other
superheavies.Comment: 7 page
A new microscopic nucleon-nucleon interaction derived from relativistic mean field theory
A new microscopic nucleon-nucleon (NN) interaction has been derived for the
first time from the popular relativistic mean field theory (RMFT) Lagrangian.
The NN interaction so obtained remarkably relate to the inbuilt fundamental
parameters of RMFT. Furthermore, by folding it with the RMFT-densities of
cluster and daughter nuclei to obtain the optical potential, it's application
is also examined to study the exotic cluster radioactive decays, and results
obtained found comparable with the successfully used M3Y phenomenological
effective NN interactions. The presently derived NN-interaction can also be
used to calculate a number of other nuclear observables.Comment: 4 Pages 2 Figure
Abrupt changes in alpha decay systematics as a manifestation of collective nuclear modes
An abrupt change in decay systematics around the N=126 neutron shell
closure is discussed. It is explained as a sudden hindrance of the clustering
of the nucleons that eventually form the particle. This is because the
clustering induced by the pairing mode acting upon the four nucleons is
inhibited if the configuration space does not allow a proper manifestation of
the pairing collectivity.Comment: 6 pages, 3 figures, submitted to Phys. Rev. C, a few new references
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Topological defects in spinor condensates
We investigate the structure of topological defects in the ground states of
spinor Bose-Einstein condensates with spin F=1 or F=2. The type and number of
defects are determined by calculating the first and second homotopy groups of
the order-parameter space. The order-parameter space is identified with a set
of degenerate ground state spinors. Because the structure of the ground state
depends on whether or not there is an external magnetic field applied to the
system, defects are sensitive to the magnetic field. We study both cases and
find that the defects in zero and non-zero field are different.Comment: 10 pages, 1 figure. Published versio
Individual and collective properties of fermions in nuclear and atomic cluster systems
Alpha-nucleus potential for alpha-decay and sub-barrier fusion
The set of parameters for alpha-nucleus potential is derived by using the
data for both the alpha-decay half-lives and the fusion cross-sections around
the barrier for reactions alpha+40Ca, alpha+59Co, alpha+208Pb. The alpha-decay
half-lives are obtained in the framework of a cluster model using the WKB
approximation. The evaluated alpha-decay half-lives and the fusion
cross-sections agreed well with the data. Fusion reactions between
alpha-particle and heavy nuclei can be used for both the formation of very
heavy nuclei and spectroscopic studies of the formed compound nuclei.Comment: 10 pages, 5 figure
Microscopic description of cluster radioactivity in actinide nuclei
Cluster radioactivity is the emission of a fragment heavier than an α particle and lighter than mass 50. The range of clusters observed in experiments goes from 14C to 32Si while the heavy mass residue is always a nucleus in the neighborhood of the doubly-magic 208Pb nucleus. Cluster radioactivity is described in this paper as very asymmetric nuclear fission. A new fission valley leading to a decay with large fragment mass asymmetry matching the cluster radioactivity products is found. The mass octupole moment is found to be more convenient than the standard quadrupole moment as the parameter driving the system to fission. The mean-field Hartree-Fock-Bogoliubov theory with the phenomenological Gogny interaction has been used to compute the cluster emission properties of a wide range of even-even actinide nuclei from 222Ra to 242Cm, where emission of the clusters has been experimentally observed. Computed half-lives for cluster emission are compared with experimental results. The noticeable agreement obtained between the predicted properties of cluster emission (namely, cluster masses and emission half-lives) and the measured data confirms the validity of the proposed methodology in the analysis of the phenomenon of cluster radioactivity. A continuous fission path through the scission point has been described using the neck parameter constraintThe work of LMR was supported by Ministerio de Ciencia e Innovacion (Spain) Grants No. FPA2009-08958 and No. FIS2009-07277, as well as by Consolider-Ingenio 2010 Programs CPAN CSD2007-00042 and MULTIDARK CSD2009- 00064. The work of MW was supported by Ministerstwo Nauki i Szkolnictwa Wyzszego (Poland) under Grant No. N N202 23113
Congenital anomalies in low- and middle-income countries: the unborn child of global surgery.
Surgically correctable congenital anomalies cause a substantial burden of global morbidity and mortality. These anomalies disproportionately affect children in low- and middle-income countries (LMICs) due to sociocultural, economic, and structural factors that limit the accessibility and quality of pediatric surgery. While data from LMICs are sparse, available evidence suggests that the true human and financial cost of congenital anomalies is grossly underestimated and that pediatric surgery is a cost-effective intervention with the potential to avert significant premature mortality and lifelong disability
Quantum tunneling in ^{277}112 and its alpha-decay chain
The -decay half lives of nuclei in the decay from element
are calculated in a WKB framework using DDM3Y interaction and experimental
Q-values. Theoretical estimation of half lives in the same quantum tunneling
model, using Q-values from the mass formula of
Muntian-Hofmann-Patyk-Sobiczewski, are also presented. Calculated results
furnish corroborating evidence for the experimental findings at RIKEN and GSI.
Certain discrepancies indicate necessity of a better mass formula. Further
experimental data with higher statistics would also be useful.Comment: 10 page
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