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Title: Constraining level densities through quantitative correlations with cross-section data

Abstract

The adopted level densities (LD) for the nuclei produced through different reaction mechanisms significantly impact the accurate calculation of cross sections for the different reaction channels. Many common LD models make simplified assumptions regarding the overall behavior of the total LD and the intrinsic spin and parity distributions of the excited states. However, very few experimental constraints are taken into account in these models: LD at neutron separation energy coming from average spacings of s- and p-wave resonances ( D0 and D1, respectively) whenever they have been previously measured, and the sometimes subjective extrapolation of discrete levels. These, however, constrain the LD only in very specific regions of excitation energy, and for specific spins and parities. This work aims to establish additional experimental constraints on LD through quantitative correlations between cross sections and LD. This allows for fitting and the determination of detailed structures in LD. For this we use the microscopic Hartree-Fock-Bogoliubov (HFB) LD as a starting point as the HFB LD provide a more realistic spin and parity distributions than phenomenological models such as Gilbert-Cameron (GC). We then associate variations predicted by the HFB model with the structure observed in double-differential cross sections at low outgoing neutron energy,more » a region that is dominated by the LD input. We also use (n, p) on 56Fe , as an example case where angle-integrated cross sections are extremely sensitive to LD. For comparison purposes we also perform calculations with the GC model. With this approach we are able to perform fits of the LD based on actual experimental data, constraining the model and ensuring its consistency. This approach can be particularly useful in extrapolating the LD to nuclei for which high-excited discrete levels and/or values of D0 or D1 are unknown. Finally, it also predicts neutron-induced inelastic γ cross sections that in some cases can differ significantly from more standard phenomenological LD models such as GC.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [3]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). National Nuclear Data Center (NNDC)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). National Nuclear Data Center (NNDC); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Massachusetts, Lowell, MA (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP)
OSTI Identifier:
1607987
Alternate Identifier(s):
OSTI ID: 1604853; OSTI ID: 1634966
Report Number(s):
BNL-213738-2020-JAAM; LA-UR-19-29483
Journal ID: ISSN 2469-9985; PRVCAN
Grant/Contract Number:  
SC0012704; AC02-98CH10886; 8933219CNA000001; 89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 101; Journal Issue: 3; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; energy level & level densities; models & methods for nuclear reactions; nucleon induced nuclear reactions; nuclear reactions; Atomic, Nuclear and Particle Physics

Citation Formats

Nobre, G. P. A., Brown, D. A., Herman, M. W., and Golas, A. Constraining level densities through quantitative correlations with cross-section data. United States: N. p., 2020. Web. doi:10.1103/PhysRevC.101.034608.
Nobre, G. P. A., Brown, D. A., Herman, M. W., & Golas, A. Constraining level densities through quantitative correlations with cross-section data. United States. doi:https://doi.org/10.1103/PhysRevC.101.034608
Nobre, G. P. A., Brown, D. A., Herman, M. W., and Golas, A. Mon . "Constraining level densities through quantitative correlations with cross-section data". United States. doi:https://doi.org/10.1103/PhysRevC.101.034608. https://www.osti.gov/servlets/purl/1607987.
@article{osti_1607987,
title = {Constraining level densities through quantitative correlations with cross-section data},
author = {Nobre, G. P. A. and Brown, D. A. and Herman, M. W. and Golas, A.},
abstractNote = {The adopted level densities (LD) for the nuclei produced through different reaction mechanisms significantly impact the accurate calculation of cross sections for the different reaction channels. Many common LD models make simplified assumptions regarding the overall behavior of the total LD and the intrinsic spin and parity distributions of the excited states. However, very few experimental constraints are taken into account in these models: LD at neutron separation energy coming from average spacings of s- and p-wave resonances ( D0 and D1, respectively) whenever they have been previously measured, and the sometimes subjective extrapolation of discrete levels. These, however, constrain the LD only in very specific regions of excitation energy, and for specific spins and parities. This work aims to establish additional experimental constraints on LD through quantitative correlations between cross sections and LD. This allows for fitting and the determination of detailed structures in LD. For this we use the microscopic Hartree-Fock-Bogoliubov (HFB) LD as a starting point as the HFB LD provide a more realistic spin and parity distributions than phenomenological models such as Gilbert-Cameron (GC). We then associate variations predicted by the HFB model with the structure observed in double-differential cross sections at low outgoing neutron energy, a region that is dominated by the LD input. We also use (n, p) on 56Fe , as an example case where angle-integrated cross sections are extremely sensitive to LD. For comparison purposes we also perform calculations with the GC model. With this approach we are able to perform fits of the LD based on actual experimental data, constraining the model and ensuring its consistency. This approach can be particularly useful in extrapolating the LD to nuclei for which high-excited discrete levels and/or values of D0 or D1 are unknown. Finally, it also predicts neutron-induced inelastic γ cross sections that in some cases can differ significantly from more standard phenomenological LD models such as GC.},
doi = {10.1103/PhysRevC.101.034608},
journal = {Physical Review C},
number = 3,
volume = 101,
place = {United States},
year = {2020},
month = {3}
}

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