1,127 research outputs found
Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission
A theoretical model of one-body nuclear friction which was developed earlier,
namely the chaos-weighted wall formula, is applied to a dynamical description
of compound nuclear decay in the framework of the Langevin equation coupled
with statistical evaporation of light particles and photons. We have used both
the usual wall formula friction and its chaos-weighted version in the Langevin
equation to calculate the fission probability and prescission neutron
multiplicity for the compound nuclei W, Pt, Pb,
Fr, Th, and Es. We have also obtained the contributions
of the presaddle and postsaddle neutrons to the total prescission multiplicity.
A detailed analysis of our results leads us to conclude that the chaos-weighted
wall formula friction can adequately describe the fission dynamics in the
presaddle region. This friction, however, turns out to be too weak to describe
the postsaddle dynamics properly. This points to the need for a suitable
explanation for the enhanced neutron emission in the postsaddle stage of
nuclear fission.Comment: RevTex, 14 pages including 5 Postscript figures, results improved by
using a different potential, conclusions remain unchanged, to appear in Phys.
Rev.
Evidence of microscopic effects in fragment mass distribution in heavy ion induced fusion-fission reactions
Our measurements of variances () in mass distributions of
fission fragments from fusion-fission reactions of light projectiles (C, O and
F) on deformed thorium targets exhibit a sharp anomalous increase with energy
near the Coulomb barrier, in contrast to the smooth variation of
for the spherical bismuth target. This departure from expectation based on a
statistical description is explained in terms of microscopic effects arising
from the orientational dependence in the case of deformed thorium targets.Comment: Replaced with revised version, to appear in Phys. Lett.
Complete Fusion Enhancement and Suppression of Weakly Bound Nuclei at Near Barrier Energies
We consider the influence of breakup channels on the complete fusion of
weakly bound systems in terms of dynamic polarization potentials. It is argued
that the enhancement of the cross section at sub-barrier energies may be
consistent with recent experimental observations that nucleon transfer, often
leading to breakup, is dominant compared to direct breakup. The main trends of
the experimental complete fusion cross section for Li + Bi are
analyzed in the framework of the DPP approach.Comment: 12 pages, 2 figure
lcc: an R package to estimate the concordance correlation, Pearson correlation and accuracy over time
Background and Objective: Observational studies and experiments in medicine,
pharmacology and agronomy are often concerned with assessing whether different
methods/raters produce similar values over the time when measuring a quantitative
variable. This article aims to describe the statistical package lcc, for are, that can
be used to estimate the extent of agreement between two (or more) methods over
the time, and illustrate the developed methodology using three real examples.
Methods: The longitudinal concordance correlation, longitudinal Pearson
correlation, and longitudinal accuracy functions can be estimated based on fixed
effects and variance components of the mixed-effects regression model. Inference is
made through bootstrap confidence intervals and diagnostic can be done via plots,
and statistical tests.
Results: The main features of the package are estimation and inference about the
extent of agreement using numerical and graphical summaries. Moreover, our
approach accommodates both balanced and unbalanced experimental designs or
observational studies, and allows for different within-group error structures, while
allowing for the inclusion of covariates in the linear predictor to control systematic
variations in the response. All examples show that our methodology is flexible and
can be applied to many different data types.
Conclusions: The lcc package, available on the CRAN repository, proved to be a
useful tool to describe the agreement between two or more methods over time,
allowing the detection of changes in the extent of agreement. The inclusion of
different structures for the variance-covariance matrices of random effects and
residuals makes the package flexible for working with different types of databases
Exploring Zeptosecond Quantum Equilibration Dynamics: From Deep-Inelastic to Fusion-Fission Outcomes in Ni+Ni Reactions
Energy dissipative processes play a key role in how quantum many-body systems
dynamically evolve towards equilibrium. In closed quantum systems, such
processes are attributed to the transfer of energy from collective motion to
single-particle degrees of freedom; however, the quantum many-body dynamics of
this evolutionary process are poorly understood. To explore energy dissipative
phenomena and equilibration dynamics in one such system, an experimental
investigation of deep-inelastic and fusion-fission outcomes in the
Ni+Ni reaction has been carried out. Experimental outcomes have
been compared to theoretical predictions using Time Dependent Hartree Fock and
Time Dependent Random Phase Approximation approaches, which respectively
incorporate one-body energy dissipation and fluctuations. Excellent
quantitative agreement has been found between experiment and calculations,
indicating that microscopic models incorporating one-body dissipation and
fluctuations provide a potential tool for exploring dissipation in low-energy
heavy ion collisions.Comment: 11 pages, 9 figures, 1 table, including Supplemental Material -
Version accepted for publication in Physical Review Letter
An evaporation-based model of thermal neutron induced ternary fission of plutonium
Ternary fission probabilities for thermal neutron induced fission of
plutonium are analyzed within the framework of an evaporation-based model where
the complexity of time-varying potentials, associated with the neck collapse,
are included in a simplistic fashion. If the nuclear temperature at scission
and the fission-neck-collapse time are assumed to be ~1.2 MeV and ~10^-22 s,
respectively, then calculated relative probabilities of ternary-fission
light-charged-particle emission follow the trends seen in the experimental
data. The ability of this model to reproduce ternary fission probabilities
spanning seven orders of magnitude for a wide range of light-particle charges
and masses implies that ternary fission is caused by the coupling of an
evaporation-like process with the rapid re-arrangement of the nuclear fluid
following scission.Comment: 25 pages, 12 figures, accepted for publication in IJMP
Combining work and child care: The experiences of mothers in Accra, Ghana
Work-family research has focused predominantly on Western women. Yet the forms of economic labour in which women are typically involved and the meaning of motherhood are context-specific. This paper aims to explore the experience of combining economic activity and child care of mothers with young children using urban Ghana as a case study. Semi-structured interviews (n=24) were conducted in three locations in the Accra Metropolitan Area. Transcripts were analysed using the general inductive approach. The results found womenâs experience of role conflict to be bi-directional. With regard to role enhancement, economic activity allowed women to provide materially for their children. The combination of work and child care had negative consequences for womenâs wellbeing. This research questions policy makersâ strategy of frequently targeting women in their roles either as generators of income, or as the primary care-takers of children by highlighting the reality of womenâs simultaneous performance of these roles
Fusion of light exotic nuclei at near-barrier energies : effect of inelastic excitation
The effect of inelastic excitation of exotic light projectiles (proton- as
well as neutron-rich) F and Be on fusion with heavy target has
been studied at near-barrier energies. The calculations have been performed in
the coupled channels approach where, in addition to the normal coupling of the
ground state of the projectile to the continuum, inelastic excitation of the
projectile to the bound excited state and its coupling to the continuum have
also been taken into consideration. The inclusion of these additional couplings
has been found to have significant effect on the fusion excitation function of
neutron-rich Be on Pb whereas the effect has been observed to be
nominal for the case of proton-rich F on the same target. The pronounced
effect of the channel coupling on the fusion process in case of Be is
attributed to its well-developed halo structure.Comment: 9 pages, 3 figures, Revtex.st
Reduced quasifission competition in fusion reactions forming neutron-rich heavy elements
Measurements of mass-angle distributions (MADs) for Cr + W reactions,
providing a wide range in the neutron-to-proton ratio of the compound system,
(N/Z)CN, have allowed for the dependence of quasifission on the (N/Z)CN to be
determined in a model-independent way. Previous experimental and theoretical
studies had produced conflicting conclusions. The experimental MADs reveal an
increase in contact time and mass evolution of the quasifission fragments with
increasing (N/Z)CN, which is indicative of an increase in the fusion
probability. The experimental results are in agreement with microscopic
time-dependent Hartree-Fock calculations of the quasifission process. The
experimental and theoretical results favor the use of the most neutron-rich
projectiles and targets for the production of heavy and superheavy nuclei.Comment: Accepted to PRC as a Rapid Communicatio
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