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Title: Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections

Abstract

Prompt {gamma}-ray production cross section measurements were made as a function of incident neutron energy (En = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These preequilibrium spin distributions were incorporated into the Hauser-Feshbach statistical reaction code GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. Neutron inelastic scattering populates 150Sm excited states either by (1) forming the compound nucleus {sup 151}Sm* and decaying by neutron emission, or (2) by the incoming neutron transferring energy to create a particle-hole pair, and thus initiating the pre-equilibrium process. These two processes produce rather different spin distributions: the momentum transfer via the pre-equilibrium process tends to be smaller than in the compound reaction. This difference in the spin population hasmore » a significant impact on the {gamma}-ray de-excitation cascade and therefore in the partial {gamma}-ray cross sections. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects was significant, e.g., for the 558-keV transition between 8{sup +} and 6{sup +} states the calculated partial {gamma}-ray production cross sections changed by 70% at E{sub n} = 20 MeV with inclusion of the spin distribution of pre-equilibrium process.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
908099
Report Number(s):
UCRL-PROC-230015
TRN: US0703616
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: International Conference on Nuclear Data for Science and Technology 2007, Nice, France, Apr 22 - Apr 27, 2007
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CROSS SECTIONS; DE-EXCITATION; DISTRIBUTION; EXCITED STATES; GERMANIUM; INELASTIC SCATTERING; LANL; MOMENTUM TRANSFER; NEUTRON EMISSION; NEUTRON SOURCES; NEUTRONS; PRODUCTION; SPALLATION; SPIN

Citation Formats

Dashdorj, D, Kawano, T, Mitchell, G E, Becker, J A, Agvaanluvsan, U, Chadwick, M, Cooper, J, Devlin, M, Fotiades, N, Garrett, P E, Kunieda, S, Nelson, R O, Wu, C Y, and Younes, W. Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections. United States: N. p., 2007. Web. doi:10.1051/ndata:07545.
Dashdorj, D, Kawano, T, Mitchell, G E, Becker, J A, Agvaanluvsan, U, Chadwick, M, Cooper, J, Devlin, M, Fotiades, N, Garrett, P E, Kunieda, S, Nelson, R O, Wu, C Y, & Younes, W. Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections. United States. doi:10.1051/ndata:07545.
Dashdorj, D, Kawano, T, Mitchell, G E, Becker, J A, Agvaanluvsan, U, Chadwick, M, Cooper, J, Devlin, M, Fotiades, N, Garrett, P E, Kunieda, S, Nelson, R O, Wu, C Y, and Younes, W. Mon . "Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections". United States. doi:10.1051/ndata:07545. https://www.osti.gov/servlets/purl/908099.
@article{osti_908099,
title = {Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections},
author = {Dashdorj, D and Kawano, T and Mitchell, G E and Becker, J A and Agvaanluvsan, U and Chadwick, M and Cooper, J and Devlin, M and Fotiades, N and Garrett, P E and Kunieda, S and Nelson, R O and Wu, C Y and Younes, W},
abstractNote = {Prompt {gamma}-ray production cross section measurements were made as a function of incident neutron energy (En = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These preequilibrium spin distributions were incorporated into the Hauser-Feshbach statistical reaction code GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. Neutron inelastic scattering populates 150Sm excited states either by (1) forming the compound nucleus {sup 151}Sm* and decaying by neutron emission, or (2) by the incoming neutron transferring energy to create a particle-hole pair, and thus initiating the pre-equilibrium process. These two processes produce rather different spin distributions: the momentum transfer via the pre-equilibrium process tends to be smaller than in the compound reaction. This difference in the spin population has a significant impact on the {gamma}-ray de-excitation cascade and therefore in the partial {gamma}-ray cross sections. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects was significant, e.g., for the 558-keV transition between 8{sup +} and 6{sup +} states the calculated partial {gamma}-ray production cross sections changed by 70% at E{sub n} = 20 MeV with inclusion of the spin distribution of pre-equilibrium process.},
doi = {10.1051/ndata:07545},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Apr 16 00:00:00 EDT 2007},
month = {Mon Apr 16 00:00:00 EDT 2007}
}

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