oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Comment on "Fission Mass Widths in $^{19}$F + $^{232}$Th, $^{16}$O + $^{235,238}$ U reactions at near barrier energies  [PDF]
T. K. Ghosh,P. Bhattacharya
Physics , 2005,
Abstract: A critical re-analysis of the experimental data to reject transfer fission component did not change the fragment mass widths and hence the conclusion regarding abrupt rise in mass widths with decreasing energy around Coulomb barrier remains unchanged
Collective spectra along the fission barrier  [cached]
Shneidman T. M.,Andreev A. V.,Pigni M. T.,Massimi C.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20123807001
Abstract: Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states) and in the intermediate wells (superdeformed and hyperdeformed states) play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster configurations in a dynamical way, permitting exchange of upper–shell nucleons between clusters. The impact of theoretical spectra on neutron–induced fission cross sections and, in combination with an improved version of the scission–point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.
Microscopic Description of Nuclear Fission: Fission Barrier Heights of Even-Even Actinides  [PDF]
J. McDonnell,N. Schunck,W. Nazarewicz
Physics , 2013,
Abstract: We evaluate the performance of modern nuclear energy density functionals for predicting inner and outer fission barrier heights and energies of fission isomers of even-even actinides. For isomer energies and outer barrier heights, we find that the self-consistent theory at the HFB level is capable of providing quantitative agreement with empirical data.
Memory effects on descent from nuclear fission barrier  [PDF]
V. M. Kolomietz,S. V. Radionov,S. Shlomo
Physics , 2001, DOI: 10.1103/PhysRevC.64.054302
Abstract: Non-Markovian transport equations for nuclear large amplitude motion are derived from the collisional kinetic equation. The memory effects are caused by the Fermi surface distortions and depend on the relaxation time. It is shown that the nuclear collective motion and the nuclear fission are influenced strongly by the memory effects at the relaxation time $\tau \geq 5\cdot 10^{-23}{\rm s}$. In particular, the descent of the nucleus from the fission barrier is accompanied by characteristic shape oscillations. The eigenfrequency and the damping of the shape oscillations depend on the contribution of the memory integral in the equations of motion. The shape oscillations disappear at the short relaxation time regime at $\tau \to 0$, which corresponds to the usual Markovian motion in the presence of friction forces. We show that the elastic forces produced by the memory integral lead to a significant delay for the descent of the nucleus from the barrier. Numerical calculations for the nucleus $^{236}$U shows that due to the memory effect the saddle-to-scission time grows by a factor of about 3 with respect to the corresponding saddle-to-scission time obtained in liquid drop model calculations with friction forces.
Thermal effects on the Fission Barrier of neutron-rich nuclei  [PDF]
Futoshi Minato,Kouichi Hagino
Physics , 2008, DOI: 10.1063/1.3039847
Abstract: We discuss the fission barrier height of neutron-rich nuclei in a r-process site at highly excited state, which is resulted from the beta-decay or the neutron-capture processes. We particularly investigate the sensitivity of the fission barrier height to the temperature, including the effect of pairing phase transition from superfluid to normal fluid phases. To this end, we use the finite-temperature Skyrme-Hartree-Fock-Bogolubov method with a zero-range pairing interaction. We also discuss the temperature dependence of the fission decay rate.
Fission barrier, damping of shell correction and neutron emission in the fission of A$\sim$200  [PDF]
K. Mahata,S. Kailas,S. S. Kapoor
Physics , 2015, DOI: 10.1103/PhysRevC.92.034602
Abstract: Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced fusion reactions has been analyzed simultaneously using a consistent prescription for fission barrier and nuclear level density incorporating shell correction and its damping with excitation energy. Good description of all the excitation functions have been achieved with a fission barrier of 21.9 $\pm$ 0.2 MeV. For this barrier height, the predicted statistical pre-fission neutrons in heavy-ion fusion-fission are much smaller than the experimental values, implying the presence of dynamical neutrons due to dissipation even at these low excitation energies ($\sim$ 50~MeV) in the mass region A $\sim$ 200. When only heavy-ion induced fission excitation functions and the pre-fission neutron multiplicities are included in the fits, the deduced best fit fission barrier depends on the assumed fission delay time during which dynamical neutrons can be emitted. A fission delay of (0.8 $\pm$ 0.1 )$\times 10^{-19}$ s has been estimated corresponding to the above fission barrier height assuming that the entire excess neutrons over and above the statistical model predictions are due to the dynamics. The present observation has implication on the study of fission time scale/ nuclear viscosity using neutron emission as a probe.
A desktop-computer simulation for exploring the fission barrier  [PDF]
B. Cameron Reed
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.34042
Abstract: A model of a fissioning nucleus that splits symmetrically both axially and equatorially is used to show how one can predict the presence of a fission barrier of several tens of MeV for nuclides of mass number A ~ 90 and of ~ 10 MeV for elements such as uranium. While the present model sacrifices some physical realism for the sake of analytic and programming simplicity, it does reproduce the general behavior of the run of fission barrier energy as a function of mass number as revealed by much more sophisticated models. Its intuitive appeal and tractability make it appropriate for presentation in a student-level “Modern Physics” class.
Free Energy Barrier for Electric Field Driven Polymer Entry into Nanoscale Channels  [PDF]
Narges Nikoofard,Hossein Fazli
Physics , 2011, DOI: 10.1103/PhysRevE.83.050801
Abstract: Free energy barrier for entry of a charged polymer into a nanoscale channel by a driving electric field is studied theoretically and using molecular dynamics simulations. Dependence of the barrier height on the polymer length, the driving field strength, and the channel entrance geometry is investigated. Squeezing effect of the electric field on the polymer before its entry to the channel is taken into account. It is shown that lateral confinement of the polymer prior to its entry changes the polymer length dependence of the barrier height noticeably. Our theory and simulation results are in good agreement and reasonably describe related experimental data.
Sub-barrier resonance fission and its effects on fission fragment properties, exemplified on 234,238U(n,f)  [cached]
Tudora A.,Hambsch F.-J.,Oberstedt S.
EPJ Web of Conferences , 2013, DOI: 10.1051/epjconf/20134206001
Abstract: The correlation between the sub-barrier resonant behaviour of fission crosssection of non-fissile actinides (pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage) around the incident energies of sub-barrier resonances is outlined and supported by quantitative results for two fissioning systems 234,238U(n,f). These quantitative results refer to both stages of the fission process: a) The pre-scission stage including the calculation of neutron induced cross-sections with focus on fission. Calculations are done in the frame of the refined statistical model for fission with sub-barrier effects also extended to take into account the multi-modal fission. b) The post-scission stage including the prompt neutron emission treated in the frame of the Point-by-Point model. Total quantities characterizing the fission fragments and the prompt neutrons obtained by averaging the Point-by-Point results as a function of fragment over the fission fragment distributions reveal variations around the energies of sub-barrier resonances in the fission crosssection.
Prediction of fission barrier height for induced fission reactions with 16O at several energies  [cached]
S Soheyli,F Alizadeh
Iranian Journal of Physics Research , 2009,
Abstract: We have calculated the fission barrier height for 16O+208Pb, 16O+209Bi, 16O+232Th, 16O+238U and 16O+248Cm systems in energy range between 90 MeV to 215 MeV. This method is based on the experimental data for angular anisotropies of fission fragments. In present work, we have used the transition state model (STM) for two different cases: the first case is without neutron emission correction and the second case is with neutron emission correction. In this paper, we have predicted the fission barrier for the two super heavy nuclei that were not reported previously with experimental methods.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.