Fission fragment mass yield deduced from density distribution in the pre-scission configuration

Warda, M.; Zdeb, A.

doi:10.1088/0031-8949/90/11/114003

Cited by 11 publications

(17 citation statements)

References 38 publications

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“…For all EFPs, q N gradually decreases prior to scission, at which it rapidly vanishes (see also Ref. [29] for a similar analysis). The above findings reinforce lingering questions about the process of fragmentation in an adiabatic theory of fission.…”

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confidence: 61%

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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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confidence: 61%

“…It is worth noting that a fairly similar technique, based on density comparison, has been successfully applied in Refs. [28,29] to identify prefragments. Results -For the 11 initial configurations on the outer turning line shown in Fig.…”

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confidence: 99%

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

et al. 2017

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“…These effects may be included e.g. by the gaussian smoothing [22] or by applying the random neck rupture (rnr) mechanism [33][34][35][36]. In the latter method, for each pre-scission shape corresponding to the scission configuration (Q sc 20 , Q sc 30 ) the probability of splitting of a nucleus at the certain position on the symmetry axis OZ along the neck is evaluated.…”

Section: Methodsmentioning

confidence: 99%

“…This is a standard parametrization of the rnr model without any fitting procedures. However a possible modification of the γ/T ratio affects the broadness of the mass yields [33]. The final fragment mass distribution is obtained as a convolution of the density current probability distribution along the p-sl and the rnr mechanism.…”

Section: Methodsmentioning

confidence: 99%

Fission dynamics of Cf252

2017

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The time-dependent generator coordinate method with the gaussian overlap approximation (TDGCM+GOA) formalism is applied to describe the fission of 252 Cf. We perform analysis of fission from the initial states laying in the energetic range from the ground state to the state located 4 MeV above the fission barrier. The fission fragment mass distributions, obtained for different parity, energy of levels and types of mixed states, are calculated and compared with experimental data. The impact of the total time of wave packet propagation on the final results is studied as well. The weak dependence of obtained mass yields on the initial conditions is shown.

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“…These represent efficient and successful methods of describing the fission process, providing a lot of physical information such as fission barrier heights, half-lives, fragment mass asymmetry, etc. [4][5][6][7][8][9][10]. They are also the basis for more advanced studies of the dynamic of fission.…”

Section: Introductionmentioning

confidence: 99%

Scission configuration in the self-consistent calculations with neck constraint

Han,

Warda,

Zdeb

et al. 2021

Preprint

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The calculations of the potential energy surface are essential in the theoretical description of the fission process. In the constrained self-consistent approach, the smooth evolution of nuclear shape is described from the ground state until a very elongated one with a narrow neck. In all microscopic calculations, the rupture of the neck at scission is associated with a substantial change of nuclear matter density distribution and rapid energy decrease. In this paper, we show that there is no discontinuity of the potential energy surface at scission when multi-constrained calculations are applied with the neck constraint. An early rupture of the neck at lower quadrupole and octupole moments is discussed as competitive with the conventional fission path. We discuss the neck properties in the scission configuration. We find that the neck radius in the asymmetric fission mode cannot decrease below 2 fm, and the nuclear matter density cannot decrease below the saturation density. In the compact fission mode, nuclear density may go down to half of the saturation density before the rupture of the neck.

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Fission fragment mass yield deduced from density distribution in the pre-scission configuration

Cited by 11 publications

References 38 publications

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

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

Fission dynamics of Cf252

Scission configuration in the self-consistent calculations with neck constraint

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