Parity-Dependence in the Nuclear Level Density

Mocelj, D.; Rauscher, T.; Langanke, K.; Martı́nez-Pinedo, G.; Pacearescu, L.; Fäßler, A.; Thielemann, Friedrich‐Karl

doi:10.1016/j.nuclphysa.2005.05.032

Cited by 8 publications

(9 citation statements)

References 6 publications

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“…It is also seen from Fig. 8 that the equilibration is quite poor for very small values of τ and therefore comparing with the results in [25], it can be argued that very small values of τ are ruled out for nuclei.…”

Section: B Parity Ratios For State Densitiessupporting

confidence: 64%

“…The general structures (i)-(iii) are clearly seen in the numerical examples shown in [25] where a method based on the Fermi-gas model has been employed. If σ t ∼ 6 − 8 MeV, equilibration in parities is expected around E ∼ 8 − 10 MeV and this is clearly seen in the examples in [25]. It is also seen from Fig.…”

Section: B Parity Ratios For State Densitiesmentioning

confidence: 89%

“…Starting with this, an iterative method is developed with inputs from the Fermi-Dirac distribution for occupancies including pairing effects and the Fermi-gas form for the total level density. In the examples studied in [25], parity ratios are found to equilibrate only around 5 − 10 MeV excitation energy. However, ab-initio interacting particle theory for parity ratios is not yet available.…”

Section: Introductionmentioning

confidence: 97%

“…Parity ratios of nuclear level densities is an important ingredient in nuclear astrophysical applications. Recently, a method based on non-interacting Fermi-gas model for protonneutron systems has been developed and the parity (π) ratios as a function of excitation energy in large number of nuclei of astrophysical interest have been tabulated [25]. The method is based on the assumption that the probability to occupy s out of N given single particle (sp) states follow Poisson distribution in the dilute limit (m << N, N → ∞ where m is the number of particles).…”

Section: Introductionmentioning

confidence: 99%

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One plus two-body random matrix ensembles with parity: Density of states and parity ratios

2011

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One plus two-body embedded Gaussian orthogonal ensemble of random matrices with parity [EGOE(1+2)-π] generated by a random two-body interaction (modeled by GOE in two particle spaces) in the presence of a mean-field, for spinless identical fermion systems, is defined, generalizing the two-body ensemble with parity analyzed by Papenbrock and Weidenmüller [Phys. Rev. C 78, 054305 (2008)], in terms of two mixing parameters and a gap between the positive (π = +) and negative (π = −) parity single particle (sp) states. Numerical calculations are used to demonstrate, using realistic values of the mixing parameters appropriate for some nuclei, that the EGOE(1+2)π ensemble generates Gaussian form (with corrections) for fixed parity eigenvalue densities (i.e. state densities). The random matrix model also generates many features in parity ratios of state densities that are similar to those predicted by a method based on the Fermi-gas model for nuclei.We have also obtained, by applying the formulation due to Chang et al [Ann. Phys. (N.Y.) 66, 137 (1971)], a simple formula for the spectral variances defined over fixed-(m 1 , m 2 ) spaces, where m 1 is the number of fermions in the +ve parity sp states and m 2 is the number of fermions in the −ve parity sp states. Similarly, using the binary correlation approximation, in the dilute limit, we have derived expressions for the lowest two shape parameters. The smoothed densities generated by the sum of fixed-(m 1 , m 2 ) Gaussians with lowest two shape corrections describe the numerical results in many situations. The model also generates preponderance of +ve parity ground states for small values of the mixing parameters and this is a feature seen in nuclear shell model results.

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Section: B Parity Ratios For State Densitiessupporting

confidence: 64%

Section: B Parity Ratios For State Densitiesmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

One plus two-body random matrix ensembles with parity: Density of states and parity ratios

2011

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“…[17] which we extend by allowing odd particle numbers, inclusion of all shells up to the 11 hω oscillator shell, and including excitations between all considered shells. Preliminary results were reported in [18,19,20,21].…”

Section: Introductionmentioning

confidence: 99%

Large-scale prediction of the parity distribution in the nuclear level density and application to astrophysical reaction rates

et al. 2007

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A generalized method to calculate the excitation-energy dependent parity ratio in the nuclear level density is presented, using the assumption of Poisson distributed independent quasi particles combined with BCS occupation numbers. It is found that it is crucial to employ a sufficiently large model space to allow excitations both from low-lying shells and to higher shells beyond a single major shell. Parity ratios are only found to equilibrate above at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect close to major shells is found where the parity opposite to the ground state parity may dominate across a range of several MeV before the parity ratio finally equilibrates. The method is suited for large-scale calculations as needed, for example, in astrophysical applications. Parity distributions were computed for all nuclei from the proton dripline to the neutron dripline and from Ne up to Bi. These results were then used to recalculate astrophysical reaction rates in a Hauser-Feshbach statistical model. Although certain transitions can be considerably enhanced or suppressed, the impact on astrophysically relevant reactions remains limited, mainly due to the thermal population of target states in stellar reaction rates.

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Cross section predictions for hydrostatic and explosive burning

Descouvemont

Rauscher

2006

Nuclear Physics A

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We review different models used for reactions involved in nuclear astrophysics. The reaction rate is defined for resonant as well as for non-resonant processes. For lowdensity nuclei, we describe the DWBA method, the potential model, the R-matrix method, and microscopic cluster models. The statistical model is developed for high-level densities. Details of calculations in the low-and high-density regimes are illustrated with new results concerning transfer reactions and level densities.

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Parity-Dependence in the Nuclear Level Density

Cited by 8 publications

References 6 publications

One plus two-body random matrix ensembles with parity: Density of states and parity ratios

One plus two-body random matrix ensembles with parity: Density of states and parity ratios

Large-scale prediction of the parity distribution in the nuclear level density and application to astrophysical reaction rates

Cross section predictions for hydrostatic and explosive burning

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