Shell effects in a paired nucleus for finite excitation energies

Jensen, A. S.; Damgaard, J.

doi:10.1016/0375-9474(73)90365-5

Cited by 159 publications

(52 citation statements)

References 21 publications

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“…The latter corresponds to a sizable nuclear deformation, where the level density increases faster than at vanishing deformation. This reduces U with increasing excitation energy, enhancing the fission probability relative to neutron emission [9,18]. This is consistent with the fact that the fission barrier in heavy nuclei is strongly influenced by shell effects [19,17], and these are washed out with increasing excitation energy.…”

supporting

confidence: 69%

Neutrino-Induced Fission of Neutron-Rich Nuclei

Kolbe

Langanke²,

Fuller³

2004

Phys. Rev. Lett.

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We calculate neutrino-induced fission cross sections for selected nuclei with Z = 84 − 92. We show that these reactions populate the daughter nucleus at excitation energies where shell effects are significantly washed out, effectively reducing the fission barrier. If the r-process occurs in the presence of a strong neutrino fluence, and electron neutrino average energies are sufficiently high, perhaps as a result of matter-enhanced neutrino flavor transformation, then neutrino-induced fission could lead to significant alteration in the r-process flow in slow outflow scenarios.In this letter we calculate neutrino capture-induced fission cross sections for heavy nuclei associated with the rprocess. Matter-enhanced neutrino flavor transformation could enhance this process in the supernova/compact object environments commonly invoked as r-process sites. Recent observations of r-process abundances in lowmetallicity, old galactical halo stars [1] show patterns which agree with the solar r-process distribution for nuclides with mass numbers A > 130, but do not reproduce the solar r-process pattern for the lighter r-process elements. In particular, these observed abundances show a peak around mass number A ∼ 195, which follows the solar r-process distribution, and enhanced structures at around A ∼ 90 and ∼ 132 which do not follow the solar pattern.It was recognized some time ago [2] that ν e capture on heavy nuclei in the post-collapse supernova environment would leave the daughter nuclei at the high excitation energies characteristic of Gamow-Teller resonances. This leaves these nuclei vulnerable to fission. Recently, Qian has demonstrated [3] that fission, induced by charged-current neutrino reactions within this neutrinodriven wind scenario [4], can account for the observed abundance patterns. In this model it is proposed that neutrino-induced fission occurs after the r-process freezes out (i.e. all initial neutrons are exhausted) and the progenitor nuclei decay to stability. It is further proposed [3] that no fission cycling occurs during the r-process, i.e. neutrino-induced reactions are unimportant during the r-process.Neutrino capture-induced fission cross sections have not been calculated before. Two aspects of nuclear physics conspire to make this process potentially important in dense environments with large neutrino fluxes: (1) the weak strength distribution in the charged current (neutrino capture) channel shows that the post-capture daughter nucleus will be left in a highly excited state; and (2) fission barriers are lower at higher excitation energy.It is expected that charged-current reactions on rprocess nuclides will have larger partial fission cross sections than neutral-current reactions, despite the fact that the latter can be induced by ν µ,τ neutrinos and their antiparticles, which, in a core bounce supernova explosion, might have larger average energies ( E ν ∼ 20 − 25 MeV) than the ν e neutrinos have ( E ν ∼ 10 MeV). For the neutron-rich nuclei along the r-process path neutrino capture cross sect...

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supporting

confidence: 69%

Neutrino-Induced Fission of Neutron-Rich Nuclei

Kolbe

Langanke²,

Fuller³

2004

Phys. Rev. Lett.

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“…[37,46,47]. It should also be considered that the sharp phase transition at the critical energy, e.g.…”

Section: Nuclear Temperaturementioning

confidence: 99%

Inconsistencies in the description of pairing effects in nuclear level densities

Schmidt

Jurado

2012

Phys. Rev. C

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Pairing correlations have a strong influence on nuclear level densities. Empirical descriptions and theoretical models have been developed to take these effects into account. The present article discusses cases, where descriptions of nuclear level densities are inconsistent or in conflict with the present understanding of nuclear properties. Phenomenological approaches consider a back-shift parameter. However, the absolute magnitude of the back-shift, which actually corresponds to the pairing condensation energy, is generally not compatible with the observation that stable pairing correlations are present in essentially all nuclei. It is also shown that in the BCS model pairing condensation energies and critical pairing energies are inconsistent for light nuclei. A modification to the composite Gilbert-Cameron level-density description is proposed, and the use of more realistic pairing theories is suggested.

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“…It is one of the main purposes of this paper to pursue the studies initiated in refs. 25,26) and to give a fully self-consistent HFB formulation of the Strutinsky method.…”

Section: Introductionmentioning

confidence: 99%

The Strutinsky method and its foundation from the Hartree-Fock-Bogoliubov approximation at finite temperature

1981

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Strutinsky's shell-correction method is investigated in the framework of the microscopical Hartree-Fock-Bogoliubov method at finite temperature (HFBT). Applying the Strutinsky energy averaging consistently to the normal and abnormal density matrices and to the entropy, we define a self-consistently averaged HFBT system as the solution of a variational problem. From the latter we derive the generalized Strutinsky energy theorem and the explicit expressions for the shell correction of a statistically excited system of BCS quasiparticles. Using numerical results of HF calculations, we demonstrate the convergence of the Strutinsky expansion and estimate the validity of the practical shell-correction approach. We also discuss the close connections of the Strutinsky energy averaging with semiclassical expansions and their usefulness for solving the average nuclear self-consistency problem. In particular we argue that the Hohenberg-Kohn theorem should hold for the averaged HFBT system and we thus provide a justification of the use of semiclassical density functionals.

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Shell effects in a paired nucleus for finite excitation energies

Cited by 159 publications

References 21 publications

Neutrino-Induced Fission of Neutron-Rich Nuclei

Neutrino-Induced Fission of Neutron-Rich Nuclei

Inconsistencies in the description of pairing effects in nuclear level densities

The Strutinsky method and its foundation from the Hartree-Fock-Bogoliubov approximation at finite temperature

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