skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei

Abstract

We calculate parity-dependent level densities for the even-even isotopes 58,62,66Fe and 58Ni and the odd-A nuclei 59Ni and 65Fe using the Shell Model Monte Carlo method. We perform these calculations in the complete fp-gds shell-model space using a pairing+quadrupole residual interaction. We find that, due to pairing of identical nucleons, the low-energy spectrum is dominated by positive parity states. Although these pairs break at around the same excitation energy in all nuclei, the energy dependence of the ratio of negative-to-positive parity level densities depends strongly on the particular nucleus of interest. We find equilibration of both parities at noticeably lower excitation energies for the odd-A nuclei 59Ni and 65Fe than for the neighboring even-even nuclei 58Ni and 66Fe.

Authors:
 [1];  [1];  [1];  [2]
  1. Gesellschaft fur Schwerionenforschung (GSI), Germany
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
932043
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review C; Journal Volume: 75; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ENERGY DEPENDENCE; EVEN-EVEN NUCLEI; EXCITATION; MONTE CARLO METHOD; NUCLEI; NUCLEONS; PARITY; RESIDUAL INTERACTIONS; SHELL MODELS; IRON ISOTOPES; NICKEL ISOTOPES

Citation Formats

Ozen, C., Langanke, K., Martinez-Pinedo, G., and Dean, David Jarvis. Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei. United States: N. p., 2007. Web. doi:10.1103/PhysRevC.75.064307.
Ozen, C., Langanke, K., Martinez-Pinedo, G., & Dean, David Jarvis. Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei. United States. doi:10.1103/PhysRevC.75.064307.
Ozen, C., Langanke, K., Martinez-Pinedo, G., and Dean, David Jarvis. Mon . "Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei". United States. doi:10.1103/PhysRevC.75.064307.
@article{osti_932043,
title = {Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei},
author = {Ozen, C. and Langanke, K. and Martinez-Pinedo, G. and Dean, David Jarvis},
abstractNote = {We calculate parity-dependent level densities for the even-even isotopes 58,62,66Fe and 58Ni and the odd-A nuclei 59Ni and 65Fe using the Shell Model Monte Carlo method. We perform these calculations in the complete fp-gds shell-model space using a pairing+quadrupole residual interaction. We find that, due to pairing of identical nucleons, the low-energy spectrum is dominated by positive parity states. Although these pairs break at around the same excitation energy in all nuclei, the energy dependence of the ratio of negative-to-positive parity level densities depends strongly on the particular nucleus of interest. We find equilibration of both parities at noticeably lower excitation energies for the odd-A nuclei 59Ni and 65Fe than for the neighboring even-even nuclei 58Ni and 66Fe.},
doi = {10.1103/PhysRevC.75.064307},
journal = {Physical Review C},
number = 6,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • We calculate parity-dependent level densities for the even-even isotopes {sup 58,62,66}Fe and {sup 58}Ni and the odd-A nuclei {sup 59}Ni and {sup 65}Fe using the shell model Monte Carlo method. We perform these calculations in the complete fp-gds shell-model space using a pairing+quadrupole residual interaction. We find that, due to pairing of identical nucleons, the low-energy spectrum is dominated by positive parity states. Although these pairs break at around the same excitation energy in all nuclei, the energy dependence of the ratio of negative-to-positive parity level densities depends strongly on the particular nucleus of interest. We find equilibration of bothmore » parities at noticeably lower excitation energies for the odd-A nuclei {sup 59}Ni and {sup 65}Fe than for the neighboring even-even nuclei {sup 58}Ni and {sup 66}Fe.« less
  • We use the auxiliary fields Monte Carlo method for the shell model in the complete (pf+0g{sub 9/2} ) shell to calculate level densities. We introduce parity projection techniques which enable us to calculate the parity dependence of the level density. Results are presented for {sup 56}Fe, where the calculated total level density is found to be in good agreement with the experimental level density. The parity-projected densities are well described by a backshifted Bethe formula, but with significant dependence of the single-particle level-density and backshift parameters on parity. We compare our exact results with those of the thermal Hartree-Fock approximation.more » {copyright} {ital 1997} {ital The American Physical Society}« less
  • We investigate the effects of single-particle structure and pairing on the equilibration of positive and negative-parity level densities for the even-even nuclei {sup 58,62,66}Fe and {sup 58}Ni and the odd-A nuclei {sup 59}Ni and {sup 65}Fe. Calculations are performed using the shell model Monte Carlo method in the complete fp-gds shell-model space using a pairing+quadrupole type residual interaction. We find for the even-even nuclei that the positive-parity states dominate at low excitation energies due to strong pairing correlations. At excitation energies at which pairs are broken, single-particle structure of these nuclei is seen to play the decisive role for themore » energy dependence of the ratio of negative-to-positive parity level densities. We also find that equilibration energies are noticeably lower for the odd-A nuclei {sup 59}Ni and {sup 65}Fe than for the neighboring even-even nuclei {sup 58}Ni and {sup 66}Fe.« less
  • We have developed an efficient isospin projection method in the shell model Monte Carlo approach for isospin-conserving Hamiltonians. For isoscalar observables this method has the advantage of being exact sample by sample. It allows us to take into account the proper isospin dependence of the nuclear interaction, thus avoiding a sign problem that such an interaction introduces in unprojected calculations. We apply the method to calculate the isospin dependence of level densities in the complete pf+g{sub 9/2} shell. We find that isospin-dependent corrections to the total level density are particularly important for N{approx}Z nuclei.
  • No abstract prepared.