Search for the fade out of a collective enhancement of the nuclear level density

Komarov, Sergey; Charity, R. J.; Chiara, C. J.; Reviol, W.; Sarantites, D. G.; Sobotka, L. G.; Caraley, A. L.; Carpenter, M. P.; Seweryniak, D.

doi:10.1103/physrevc.75.064611

Cited by 27 publications

(17 citation statements)

References 27 publications

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“…Collective excitations that can be expressed as a coherent superposition of single-particle excitations are expected to disappear at higher excitation energies, if the nuclear temperature becomes comparable with the energies of single-particle excitations [15]. However, the energy range, where this happens, is still under debate, since the available experimental indications are rather indirect and contradictory [16,17].…”

Section: Salient Features Of Nuclear Level Densitiesmentioning

confidence: 99%

“…The back-shift parameter of the Fermi-gas part is then given by the usual matching conditions. The fade out of the collective enhancement remains an open problem, but experimental results [16] and theoretical arguments [17] suggest that this feature is rather inconspicuous. MeV, and the level density in the Fermi-gas regime is enhanced by about a factor of 50 with respect to the conventional composite Gilbert-Cameron level density.…”

Section: Composite Gilbert-cameron Level Densitymentioning

confidence: 99%

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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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Section: Salient Features Of Nuclear Level Densitiesmentioning

confidence: 99%

Section: Composite Gilbert-cameron Level Densitymentioning

confidence: 99%

Inconsistencies in the description of pairing effects in nuclear level densities

Schmidt

Jurado

2012

Phys. Rev. C

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“…Other authors have suggested that collective effects are not necessary to reproduce EvR cross sections away from the N = 126 shell because the effects are weak [15] or because the fission barriers are much smaller than predicted by theory [16]. Additionally, α-particle spectra were poorly reproduced when CELD was considered [17]. It is clear that further investigation into the CELD phenomenon is warranted.…”

Section: Introductionmentioning

confidence: 99%

Hot fusion-evaporation cross sections ofCa44-induced reactions with lanthanide targets

et al. 2015

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Background: Previously reported cross sections of 45 Sc-induced reactions with lanthanide targets are much smaller than 48 Ca-induced reactions on the same targets. 44 Ca is one proton removed from 45 Sc and could be used to produce nuclei with a relative neutron content between those produced in the 45 Sc-and 48 Ca-induced reactions.Purpose: As part of a systematic investigation of fusion-evaporation reactions, cross sections of 44 Cainduced reactions on lanthanide targets were measured. These results are compared to available data for 48 Sc-induced fusion-evaporation cross sections on the same lanthanide targets. Collectively, these data provide insight into the importance of the survival against fission of excited compound nuclei produced near spherical shell closures. Gd once differences in capture cross sections and compound nucleus formation probabilities are corrected for. Methods Conclusions: Excitation functions were measured in44 Ca-induced reactions on lanthanide targets. Evaporation residue cross sections were two orders of magnitude larger than 45 Sc-induced reactions on the same targets due to an increase in the survival probability of the compound nucleus. However, little evidence of cross section enhancement due to shell stabilization of the compound nucleus was observed.

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“…With smoothing shell gaps, it is harder to distinguish between rotational and intrinsic motion. Recent experiments in nuclei, where low-lying collective excitations are well known, did not find clear phenomena of collective enhancement and its fade-out [48].…”

Section: Shell-model Predictions and Mean-field Combinatoricsmentioning

confidence: 99%

Nuclear level density: Shell-model approach

Sen'kov

Zelevinsky

2016

Phys. Rev. C

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The knowledge of the nuclear level density is necessary for understanding various reactions including those in the stellar environment. Usually the combinatorics of Fermi-gas plus pairing is used for finding the level density. Recently a practical algorithm avoiding diagonalization of huge matrices was developed for calculating the density of many-body nuclear energy levels with certain quantum numbers for a full shell-model Hamiltonian. The underlying physics is that of quantum chaos and intrinsic thermalization in a closed system of interacting particles. We briefly explain this algorithm and, when possible, demonstrate the agreement of the results with those derived from exact diagonalization. The resulting level density is much smoother than that coming from the conventional mean-field combinatorics. We study the role of various components of residual interactions in the process of thermalization, stressing the influence of incoherent collision-like processes. The shell-model results for the traditionally used parameters are also compared with standard phenomenological approaches.

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Search for the fade out of a collective enhancement of the nuclear level density

Cited by 27 publications

References 27 publications

Inconsistencies in the description of pairing effects in nuclear level densities

Inconsistencies in the description of pairing effects in nuclear level densities

Hot fusion-evaporation cross sections ofCa44-induced reactions with lanthanide targets

Nuclear level density: Shell-model approach

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