Test of nuclear level density inputs for Hauser-Feshbach model calculations

Voinov, A.; Grimes, S. M.; Brune, C. R.; Hornish, M. J.; Massey, T. N.; Salas, A. Salvador

doi:10.1103/physrevc.76.044602

Cited by 51 publications

(64 citation statements)

References 23 publications

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“…Then the task is to predict the level density of the system at higher excitation energy, in the region beyond direct measurements resolving individual quantum states. Practically, the relevant factual milestones, apart from the low-lying spectroscopy, are the regions of isolated neutron resonances near neutron separation energy and the results of the Oslo method and related experimental approaches [1][2][3][4]. Of course, any practical shell-model Hamiltonian loses its validity outside of the truncated orbital space where this Hamiltonian was expected to work.…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%

Nuclear level density: Shell-model approach

Sen'kov

Zelevinsky

2016

Phys. Rev. C

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“…When either background subtraction procedure is applied to the 208 Pb(p, p ) data, level densities of 1 − states in the energy region of the IVGDR can indeed be extracted and compared to a variety of phenomenological and microscopic models. This experimental method to determine level densities is complementary to approaches based on compound nucleus γ-decay [22] and particle emission [23], or thermal neutron capture [24].…”

Section: Introductionmentioning

confidence: 99%

Fine structure of the isovector giant dipole resonance inPb208: Characteristic scales and level densities

et al. 2014

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Background: The electric isovector giant dipole resonance (IVGDR) in208 Pb has been measured with high energy resolution with the (p, p ) reaction under extreme forward angles [A. Tamii et al., Phys. Rev. Lett. 107, 062502 (2011)] and shows considerable fine structure.Purpose: The aim of the present work is to extract scales characterizing the observed fine structure and to relate them to dominant decay mechanisms of giant resonances. Furthermore, the level density of J π = 1 − states is determined in the energy region of the IVGDR.Methods: Characteristic scales are extracted from the spectra with a wavelet analysis based on continuous wavelet transforms.Comparison with corresponding analyses of B(E1) strength distributions from microscopic model calculations in the framework of the quasiparticle phonon model and the relativistic random phase approximation allow to identify giant resonance decay mechanisms responsible for the fine structure. The level density of 1 − states is related to local fluctuations of the cross sections in the energy region of the IVGDR, where contributions from states with other spin-parities can be neglected. The magnitude of the fluctuations is determined by the autocorrelation function.Results: Scales in the fine structure of the IVGDR in 208 Pb are found at 80, 130, 220, 430, 640, 960 keV, and at 1.75 MeV. The values of the most prominent scales can be reasonably well reproduced by the microscopic calculations although they generally yield a smaller number of scales.. The inclusion of complex configurations in the calculations changes the E1 strength distributions but the impact on the wavelet power spectra and characteristic scales is limited. The level density of 1 − states is extracted in the excitation energy range 9 − 12.5 MeV and compared to a variety of phenomenological and microscopic models. Conclusions:In both models the major scales are already present at the one-particle one-hole level indicating Landau damping as a dominant mechanism responsible for the fine structure of the IVGDR in contrast to the isoscalar giant quadrupole resonance, where fine structure arises from the coupling to low-lying surface vibrations. The back-shifted Fermi gas model parameterization of Rauscher et al., Phys. Rev. C 56, 1613 describes the level-density data well, while other phenomeological and microscopic approaches fail to reproduce absolute values or the energy dependence or both.

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“…The latter was measured with a 10 MeV 3 He beam, also at the Edwards Accelerator Laboratory [3]. In Fig.…”

Section: Analysis Of Experimental Spectramentioning

confidence: 99%

“…Because of the stopping power of the ∆E detector, only protons with energies above about 7 MeV were registered. The low energy portion of the proton spectrum, with proton energies up to about 10 MeV, was measured with the charged-particle spectrometer [3], in which the energy and the particle type were determined by the energy deposited in 1500 µm Si detectors and the flight time for the 2 m flight paths between the target and the detector. The measurement was carried out at 157.5…”

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confidence: 99%

Equilibrium and pre-equilibrium processes in theMn55(Li6
Voinov
¹
,
Grimes
²
,
Brune
³

et al. 2011
Phys. Rev. C
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Test of nuclear level density inputs for Hauser-Feshbach model calculations

Cited by 51 publications

References 23 publications

Nuclear level density: Shell-model approach

Nuclear level density: Shell-model approach

Fine structure of the isovector giant dipole resonance inPb208: Characteristic scales and level densities

Equilibrium and pre-equilibrium processes in theMn55(Li6
Voinov
¹
,
Grimes
²
,
Brune
³

et al. 2011
Phys. Rev. C
Self Cite
2
0
0
0
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Test of nuclear level density inputs for Hauser-Feshbach model calculations

Cited by 51 publications

References 23 publications

Nuclear level density: Shell-model approach

Nuclear level density: Shell-model approach

Fine structure of the isovector giant dipole resonance inPb208: Characteristic scales and level densities

Equilibrium and pre-equilibrium processes in theMn55(Li6Voinov1, Grimes2, Brune3 et al. 2011Phys. Rev. CSelf Cite2000View full textAdd to dashboardCite

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Equilibrium and pre-equilibrium processes in theMn55(Li6
Voinov
¹
,
Grimes
²
,
Brune
³

et al. 2011
Phys. Rev. C
Self Cite
2
0
0
0
View full text Add to dashboard Cite