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

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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, ... continued below

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6 p. (0.1 MB)

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Dashdorj, D; Kawano, T; Mitchell, G E; Becker, J A; Agvaanluvsan, U; Chadwick, M et al. April 16, 2007.

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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.

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6 p. (0.1 MB)

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  • Presented at: International Conference on Nuclear Data for Science and Technology 2007, Nice, France, Apr 22 - Apr 27, 2007

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  • Report No.: UCRL-PROC-230015
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 908099
  • Archival Resource Key: ark:/67531/metadc891467

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • April 16, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • April 13, 2017, 6:30 p.m.

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Dashdorj, D; Kawano, T; Mitchell, G E; Becker, J A; Agvaanluvsan, U; Chadwick, M et al. Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections, article, April 16, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc891467/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.