Role of pairing degrees of freedom and higher multipolarity deformations in spontaneous fission process

Łojewski, Z.; Staszczak, A.

doi:10.1016/s0375-9474(99)00328-0

Cited by 28 publications

(31 citation statements)

References 30 publications

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“…While the reduction of the collective action by pairing fluctuations has been pointed out in earlier works [10,13,[15][16][17] and also very recently in a self-consistent approach [38], our work shows that pairing dynamics can profoundly impact penetration probability, that is, effective fission barriers, by restoring symmetries spontaneously broken in a static approach.…”

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confidence: 58%

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Pairing-induced speedup of nuclear spontaneous fission

et al. 2014

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Background: Collective inertia is strongly influenced at the level crossing at which quantum system changes diabatically its microscopic configuration. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of those configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes.Purpose: To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264 Fm and 240 Pu using the state-of-the-art self-consistent framework. Methods:We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM * and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates.Results: Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264 Fm, where the effect of triaxiality on the fission barrier is large, the geometry of fission pathway in the space of shape degrees of freedom is weakly impacted by pairing. This is not the case for 240 Pu where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. Conclusions:The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.PACS numbers: 24.75.+i, 25.85.Ca, 21.60.Jz, 21.30.Fe, 27.90.+b Introduction -Nuclear fission is a fundamental phenomenon that is a splendid example of a large-amplitude collective motion of a system in presence of many-body tunneling. The corresponding equations involve potential, dissipative, and inertial terms [1]. The individualparticle motion gives rise to shell effects that influence the fission barriers and shapes on the way to fission, and also strongly impact the inertia tensor through the crossings of single-particle levels and resulting configuration changes [2][3][4]. The residual interaction between crossing configurations is strongly affected by nucleonic pairing: the larger pairing gap ∆ the more adiabatic is the collective motion [5][6][7][8][9].

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confidence: 58%

“…This means that in searching for the least action trajectory the gap parameter should be treated as a dynamical variable. Indeed, macroscopicmicroscopic studies [15][16][17][18] demonstrated that pairing fluctuations can significantly reduce the collective action; hence, affect predicted spontaneous fission lifetimes.…”

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Pairing-induced speedup of nuclear spontaneous fission

et al. 2014

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“…When the gap parameter is treated as a dynamical variable, an en-hancement of pairing correlations reduces the effective inertia and thus minimizes the action integral S along the fission path [11]. A number of studies of SF have shown that the coupling of pairing fluctuations with the fission mode can significantly reduce the estimated fission lifetimes [12][13][14][15][16][17][18][19].…”

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confidence: 99%

Multidimensionally-constrained relativistic mean-field study of spontaneous fission: Coupling between shape and pairing degrees of freedom

et al. 2016

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Background: Studies of fission dynamics, based on nuclear energy density functionals, have shown that the coupling between shape and pairing degrees of freedom has a pronounced effect on the nonperturbative collective inertia and, therefore, on dynamic (least-action) spontaneous fission paths and half-lives.Purpose: To analyze effects of particle-number fluctuation degree of freedom on symmetric and asymmetric spontaneous fission (SF) dynamics, and compare with results of recent studies based on the self-consistent HartreeFock-Bogoliubov (HFB) method.Methods: Collective potentials and nonperturbative cranking collective inertia tensors are calculated using the multidimensionally-constrained relativistic mean-field (MDC-RMF) model. Pairing correlations are treated in the BCS approximation using a separable pairing force of finite range. Pairing fluctuations are included as a collective variable using a constraint on particle-number dispersion. Fission paths are determined with the dynamic programming method by minimizing the action in multidimensional collective spaces. Results: The dynamics of spontaneous fission of264 Fm and 250 Fm are explored. Fission paths, action integrals and corresponding half-lives computed in the three-dimensional collective space of shape and pairing coordinates, using the relativistic functional DD-PC1 and a separable pairing force of finite range, are compared with results obtained without pairing fluctuations. Results for 264 Fm are also discussed in relation with those recently obtained using the HFB model. Conclusions:The inclusion of pairing correlations in the space of collective coordinates favors axially symmetric shapes along the dynamic path of the fissioning system, amplifies pairing as the path traverses the fission barriers, significantly reduces the action integral and shortens the corresponding SF half-life.

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“…In a second step, a constraint is introduced in the self-consistent calculation in order to impose identical spatial distributions to neutrons and protons. The resulting effect on the shape and height of fission barriers can be viewed as an estimate of the influence of the assumption usually made in macroscopic-microscopic Strutinsky-type models (see, e.g., [16][17][18]), that the neutron and proton potentials have the same multipole deformations.…”

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Effect of Differences in Proton and Neutron Density Distributions on Fission Barriers

Berger

Pomorski²

2000

Phys. Rev. Lett.

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The neutron and proton density distributions obtained in constrained Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission paths of 232Th, 236U, 238U, and 240Pu are analyzed. Significant differences in the multipole deformations of neutron and proton densities are found. The effect on potential energy surfaces and on barrier heights is studied under an additional constraint by imposing similar spatial distributions to neutrons and protons, as assumed in macroscopic-microscopic models.

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Role of pairing degrees of freedom and higher multipolarity deformations in spontaneous fission process

Cited by 28 publications

References 30 publications

Pairing-induced speedup of nuclear spontaneous fission

Pairing-induced speedup of nuclear spontaneous fission

Multidimensionally-constrained relativistic mean-field study of spontaneous fission: Coupling between shape and pairing degrees of freedom

Effect of Differences in Proton and Neutron Density Distributions on Fission Barriers

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