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Title: Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections

Abstract

Cross section measurements were made of prompt gamma-ray production as a function of neutron energy using the germanium array for neutron induced excitations (GEANIE) at LANSCE. Measuring the prompt reaction gamma rays as a function of incident neutron energy provides more precise understanding of the spins populated by the pre-equilibrium reaction. The effect of the spin distribution in pre-equilibrium reactions has been investigated using the GNASH reaction code. Widely used classical theories such as the exciton model usually assume that the spin distribution of the pre-equilibrium reaction is the same as the spin distribution of the compound nucleus reaction mechanism. In the present approach, the pre-equilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). This pre-equilibrium spin distribution was incorporated into the GNASH code and the gamma-ray production cross sections were calculated and compared with experimental data. Spin distributions peak at lower spin when calculated with the FKK formulation than with the Compound Nuclear theory. The measured partial gamma-ray cross sections reflect this spin difference. Realistic treatment of the spin distribution improves the accuracy of calculations of gamma-ray production cross sections.

Authors:
;  [1]; ;  [2]; ; ; ; ;  [3];  [4];  [5]
  1. North Carolina State University, Raleigh, NC and Triangle Universities Nuclear Laboratory, Durham, NC (United States)
  2. Lawrence Livermore National Laboratory, Livermore, CA (United States)
  3. Los Alamos National Laboratory Los Alamos, NM (United States)
  4. University of Guelph, Guelph, Ontario (Canada)
  5. Japan Atomic Energy Agency, Tokai (Japan)
Publication Date:
OSTI Identifier:
21143143
Resource Type:
Journal Article
Journal Name:
AIP Conference Proceedings
Additional Journal Information:
Journal Volume: 1005; Journal Issue: 1; Conference: CNR 2007: 2007 international workshop on compound-nuclear reactions and related topics, Yosemite National Park, CA (United States), 22-26 Oct 2007; Other Information: DOI: 10.1063/1.2920722; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-243X
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COMPOUND-NUCLEUS REACTIONS; CROSS SECTIONS; EXCITATION; EXCITON MODEL; G CODES; GAMMA RADIATION; NEUTRON REACTIONS; NEUTRONS; NUCLEAR THEORY; PROMPT GAMMA RADIATION; QUANTUM MECHANICS; SCATTERING; SPIN; STATISTICAL MODELS

Citation Formats

Dashdorj, D, Mitchell, G E, Becker, J A, Wu, C Y, Chadwick, M B, Devlin, M, Fotiades, N, Kawano, T, Nelson, R O, Garrett, P E, and Kunieda, S. Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections. United States: N. p., 2008. Web. doi:10.1063/1.2920722.
Dashdorj, D, Mitchell, G E, Becker, J A, Wu, C Y, Chadwick, M B, Devlin, M, Fotiades, N, Kawano, T, Nelson, R O, Garrett, P E, & Kunieda, S. Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections. United States. https://doi.org/10.1063/1.2920722
Dashdorj, D, Mitchell, G E, Becker, J A, Wu, C Y, Chadwick, M B, Devlin, M, Fotiades, N, Kawano, T, Nelson, R O, Garrett, P E, and Kunieda, S. 2008. "Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections". United States. https://doi.org/10.1063/1.2920722.
@article{osti_21143143,
title = {Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections},
author = {Dashdorj, D and Mitchell, G E and Becker, J A and Wu, C Y and Chadwick, M B and Devlin, M and Fotiades, N and Kawano, T and Nelson, R O and Garrett, P E and Kunieda, S},
abstractNote = {Cross section measurements were made of prompt gamma-ray production as a function of neutron energy using the germanium array for neutron induced excitations (GEANIE) at LANSCE. Measuring the prompt reaction gamma rays as a function of incident neutron energy provides more precise understanding of the spins populated by the pre-equilibrium reaction. The effect of the spin distribution in pre-equilibrium reactions has been investigated using the GNASH reaction code. Widely used classical theories such as the exciton model usually assume that the spin distribution of the pre-equilibrium reaction is the same as the spin distribution of the compound nucleus reaction mechanism. In the present approach, the pre-equilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). This pre-equilibrium spin distribution was incorporated into the GNASH code and the gamma-ray production cross sections were calculated and compared with experimental data. Spin distributions peak at lower spin when calculated with the FKK formulation than with the Compound Nuclear theory. The measured partial gamma-ray cross sections reflect this spin difference. Realistic treatment of the spin distribution improves the accuracy of calculations of gamma-ray production cross sections.},
doi = {10.1063/1.2920722},
url = {https://www.osti.gov/biblio/21143143}, journal = {AIP Conference Proceedings},
issn = {0094-243X},
number = 1,
volume = 1005,
place = {United States},
year = {Thu Apr 17 00:00:00 EDT 2008},
month = {Thu Apr 17 00:00:00 EDT 2008}
}