Mass yields and kinetic energy of fragments from fission of highly-excited nuclei with A≲220

Denisov, V. Yu.; Margitych, T.O.; Sedykh, I. Yu.

doi:10.1016/j.nuclphysa.2016.11.007

Cited by 39 publications

(7 citation statements)

References 77 publications

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“…In this case, they do not depend on the fragments shell structure since it is washed out at high energies, so that the fissioning nucleus tends to behave as a liquid drop [8]. Denisov et al [9] found that the height of the so-called two-body saddle point is larger than the height of the one-body saddle point (i.e., the fission barrier) for nuclei with A 220. For heavier nuclei, it is the opposite, so that the yields are expected to be sensitive to the trajectories descending from the one-body saddle point to the scission point.…”

Section: Introductionmentioning

confidence: 99%

Fully microscopic scission-point model to predict fission fragment observables

et al. 2019

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We present an upgraded version of the SPY model, called SPY2 for version 2 of the scission point yield, to estimate mainly the yields and the kinetic energy distributions of fission fragments: The theoretical framework is similar to our previous version, i.e., a statistical scission point model, but this version is based on fully microscopic nuclear ingredients describing the fragments properties at the scission point. These include the static properties of some 7000 nuclei at 120 axial quadrupole deformations, such as binding energies, proton densities, single-particle level schemes, and states densities, coherently calculated within the constrained Hartree-Fock-Bogoliubov model on the basis of the Skyrme BSk27 interaction. The use of microscopic ingredients has been extended to the proton density distribution and the nuclear states densities. Considering realistic proton densities of fragments allows us to improve the definition of the scission point as well as the prediction of the kinetic energy distribution and to link the kinetic energy to the diffuseness of the fragments' proton density. New microscopic nuclear states densities improve the general coherence of the model, in particular regarding the inclusion of the odd-even pairing effect. In this updated SPY2 version, the calculation of the fission yields and kinetic energy distributions is significantly improved and found to be in relatively good agreement with experiments, at least qualitatively. A detailed study is performed for three well known fissioning systems, namely, thermal neutron induced fission of 235 U and 239 Pu and spontaneous fission of 252 Cf. A systematic analysis of the fission mode as well as mean fragments deformation and total kinetic energies has been performed for some 2000 fissioning nuclei with 78 Z 110 lying between the proton and neutron drip lines.

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Section: Introductionmentioning

confidence: 99%

Fully microscopic scission-point model to predict fission fragment observables

et al. 2019

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“…In this regime, stochastic transport theories have been successfully applied to describe the energy transfer between the collective and intrinsic degrees of freedom of the fissioning nucleus [21,34,35]. Among such theories, dynamical approaches based on the Langevin equation and its derivatives have been successful in reproducing fission dynamics [22,[36][37][38][39][40].…”

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Dynamical model calculation to reconcile the nuclear fission lifetime from different measurement techniques

Kannan¹,

Sadhukhan²,

Agrawal³

et al. 2018

Phys. Rev. C

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The pre-scission particle multiplicities suggest a lifetime of ∼ 10 −20 s for the nuclear fission to occur which is in contrast to the fission lifetime ∼ 10 −18 s as predicted by atomic probe. This long standing ambiguity, arising due to the orders of magnitude differences among the fission lifetime measured from the nuclear and atomic probes, has been addressed within a dynamical model which includes the contributions from the nuclear shell effects. We show that, at lower excitation energies, these two probes decouples as the fissioning system survives for a long time without any particle evaporation. We also consider a wide range of reactions to study the impact of the excitation energy of compound nucleus on the fission dynamics in general. Our model predicts the average fission life time of superheavy nucleus 302 120, to be more than 10 −18 s which is in reasonable agreement with the recent experiments.

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“…In this regime, stochastic transport theories have been successfully applied to describe the energy transfer between the collective and intrinsic degrees of freedom of the fissioning nucleus [18,19]. Among such theories, dynamical approaches based on the Langevin equation and its derivatives have been successful in reproducing fission dynamics, including fission yields [19][20][21][22][23].…”

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confidence: 99%

Formation and distribution of fragments in the spontaneous fission of 240Pu

et al. 2017

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Background: Fission is a fundamental decay mode of heavy atomic nuclei. The prevalent theoretical approach is based on mean-field theory and its extensions, where fission is modeled as a large amplitude motion of a nucleus in a multi-dimensional collective space. One of the important observables characterizing fission is the charge and mass distribution of fission fragments.Purpose: The goal of this paper is to better understand the structure of fission fragment distributions by investigating the competition between the static structure of the collective manifold and stochastic dynamics. In particular, we study the characteristics of the tails of yield distributions, which correspond to very asymmetric fission into a very heavy and a very light fragment. Methods:We use the stochastic Langevin framework to simulate the nuclear evolution after the system tunnels through the multi-dimensional potential barrier. For a representative sample of different initial configurations along the outer turning-point line, we define effective fission paths by computing a large number of Langevin trajectories. We extract the relative contribution of each such path to the fragment distribution. We then use nucleon localization functions along effective fission pathways to analyze the characteristics of prefragments at pre-scission configurations.Results: We find that non-Newtonian Langevin trajectories, strongly impacted by the random force, produce the tails of the fission fragment distribution of 240 Pu. The prefragments deduced from nucleon localizations are formed early and change little as the nucleus evolves towards scission. On the other hand, the system contains many nucleons that are not localized in the prefragments, even near the scission point. Such nucleons are rapidly distributed at scission to form the final fragments. Fission prefragments extracted from direct integration of the density and from the localization functions typically differ by more than 30 nucleons, even near scission.Conclusions: Our study shows that only theoretical models of fission that account for some form of dissipative/stochastic dynamics can give an accurate description of the structure of fragment distributions. In particular, it should be nearly impossible to predict the tails of these distributions within the standard formulation of timedependent density functional theory. At the same time, the large number of non-localized nucleons during fission suggests that adiabatic approaches, where the interplay between intrinsic excitations and collective dynamics is neglected, are ill-suited to describe fission fragment properties, in particular their excitation energy.Introduction -A better understanding of nuclear fission is essential for different branches of basic sciences and applications. Fission governs the existence and stability of heavy and superheavy elements [1][2][3]. In nuclear astrophysics, fission rates and the related fission fragment distributions are key inputs to investigate the origin of elements heavier than iron [4][5][6]. ...

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Mass yields and kinetic energy of fragments from fission of highly-excited nuclei with A≲220

Cited by 39 publications

References 77 publications

Fully microscopic scission-point model to predict fission fragment observables

Fully microscopic scission-point model to predict fission fragment observables

Dynamical model calculation to reconcile the nuclear fission lifetime from different measurement techniques

Formation and distribution of fragments in the spontaneous fission of 240Pu

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