Theory of macroscopic fission dynamics

Адеев, Г. Д.; Pashkevich, V. V.

doi:10.1016/0375-9474(89)90679-9

Cited by 56 publications

(33 citation statements)

References 36 publications

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“…Dynamical calculations revealed that, depending on the nature of the collective degree of freedom considered, dynamical effects induce a kind of memory on the fission trajectory due to the influence of dissipative and inertial forces [28]. The corresponding characteristic memory time determines, after which time a specific coordinate value is forgotten and how long it takes for this coordinate to adjust to modified conditions.…”

Section: Characteristic Times Of Stochastic Processesmentioning

confidence: 99%

“…However, it is well known [85] that the statistical model, applied to the scission-point configuration, is unable of explaining the variances of the mass and energy distributions and their dependence on the compound-nucleus fissility parameter. Studies of Adeev and Pashkevich [28] suggest that dynamical effects due to the influence of inertia and dissipation can be approximated by considering the properties of the system at an earlier time. That means that the statistical model may give reasonable results if it is applied to a configuration that depends on the typical time constant of the collective coordinate considered.…”

Section: E Quantum Oscillators Of Normal Modesmentioning

confidence: 99%

“…[28,[86][87][88]. It was found that the width of the mass distribution varies with energy E according to the relation σ 2 q = √ E/a C that corresponds to the classical limit with the temperature defined by the Fermi-gas nuclear level density.…”

Section: E Quantum Oscillators Of Normal Modesmentioning

confidence: 99%

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General Description of Fission Observables: GEF Model Code

Schmidt

Jurado

Amouroux

et al. 2016

Nuclear Data Sheets

430

421

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The GEF ("GEneral description of Fission observables") model code is documented. It describes the observables for spontaneous fission, neutron-induced fission and, more generally, for fission of a compound nucleus from any other entrance channel, with given excitation energy and angular momentum. The GEF model is applicable for a wide range of isotopes from Z = 80 to Z = 112 and beyond, up to excitation energies of about 100 MeV. The results of the GEF model are compared with fission barriers, fission probabilities, fission-fragment mass-and nuclide distributions, isomeric ratios, total kinetic energies, and prompt-neutron and prompt-gamma yields and energy spectra from neutron-induced and spontaneous fission. Derived properties of delayed neutrons and decay heat are also considered.The GEF model is based on a general approach to nuclear fission that explains a great part of the complex appearance of fission observables on the basis of fundamental laws of physics and general properties of microscopic systems and mathematical objects. The topographic theorem is used to estimate the fission-barrier heights from theoretical macroscopic saddle-point and ground-state masses and experimental ground-state masses. Motivated by the theoretically predicted early localisation of nucleonic wave functions in a necked-in shape, the properties of the relevant fragment shells are extracted. These are used to determine the depths and the widths of the fission valleys corresponding to the different fission channels and to describe the fission-fragment distributions and deformations at scission by a statistical approach. A modified composite nuclear-level-density formula is proposed. It respects some features in the superfluid regime that are in accordance with new experimental findings and with theoretical expectations. These are a constant-temperature behaviour that is consistent with a considerably increased heat capacity and an increased pairing condensation energy that is consistent with the collective enhancement of the level density. The exchange of excitation energy and nucleons between the nascent fragments on the way from saddle to scission is estimated according to statistical mechanics. As a result, excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment in the superfluid regime. This description reproduces some rather peculiar observed features of the prompt-neutron multiplicities and of the even-odd effect in fission-fragment Z distributions. For completeness, some conventional descriptions are used for calculating pre-equilibrium emission, fission probabilities and statistical emission of neutrons and gamma radiation from the excited fragments. Preference is given to simple models that can also be applied to exotic nuclei compared to more sophisticated models that need precise empirical input of nuclear properties, e.g. spectroscopic information.The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission obs...

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Section: Characteristic Times Of Stochastic Processesmentioning

confidence: 99%

Section: E Quantum Oscillators Of Normal Modesmentioning

confidence: 99%

See 1 more Smart Citation

General Description of Fission Observables: GEF Model Code

Schmidt

Jurado

Amouroux

et al. 2016

Nuclear Data Sheets

430

421

View full text Add to dashboard Cite

show abstract

“…However, it is well known [6] that the statistical model, applied to the scission-point configuration, is unable of explaining the variances of the mass and energy distributions and their dependence on the compound-nucleus fissility parameter. The solution of the problem has been given by Adeev and Pashkevich [7] by considering the influence of inertia and dissipation. Their calculations suggest that the width of the distribution of a specific normal mode is approximately given by the fluctuation of the corresponding oscillator with an effective stiffness that is equal to the stiffness of the potential somewhere between saddle and scission.…”

Section: Dynamical Effectsmentioning

confidence: 99%

Modelling the widths of fission observables in GEF

Jurado

Schmidt

2013

EPJ Web of Conferences

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Abstract. The widths of the mass distributions of the different fission channels are traced back to the probability distributions of the corresponding quantum oscillators that are coupled to the heat bath, which is formed by the intrinsic degrees of freedom of the fissioning system under the influence of pairing correlations and shell effects. Following conclusion from stochastic calculations of Adeev and Pashkevich, an early freezing due to dynamical effects is assumed. It is shown that the mass width of the fission channels in low-energy fission is strongly influenced by the zero-point motion of the corresponding quantum oscillator. The observed variation of the mass widths of the asymmetric fission channels with excitation energy is attributed to the energy-dependent properties of the heat bath and not to the population of excited states of the corresponding quantum oscillator.

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“…Nuclear fission is a very complicated process, which can be considered as a large amplitude collective motion described by the Fokke~Planck equation (FPE) [1][2][3] or the Langevin equation (LE) [zk6]. Theoretically, a reasonable study of nuclear fission requires to consider multidimensional effects, a coordinate-dependent inertia and friction, a realistic potential, a complete dynamical process and so on.…”

Section: Introductionmentioning

confidence: 99%

Systematic studies of fission fragment kinetic energy distributions by Langevin simulations

Bao

Zhuo

1995

Z. Physik A - Hadrons and Nuclei

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Abstract. Fission fluctuation-dissipation dynamics of heavy nuclei has been studied using Langevin Monte Carlo simulations. The covariant form of the fission transport equation and the coefficients related to it are investigated. To learn about the influence of the dynamics from the ground state to the saddle point on the kinetic energy distributions we have studied various systems and compared the calculations both starting from the ground state and from the saddle point. Both the mean total kinetic energy of the fission fragments and its variances can fit with the experimental values in terms of a finite neck radius as scission condition.

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Theory of macroscopic fission dynamics

Cited by 56 publications

References 36 publications

General Description of Fission Observables: GEF Model Code

General Description of Fission Observables: GEF Model Code

Modelling the widths of fission observables in GEF

Systematic studies of fission fragment kinetic energy distributions by Langevin simulations

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