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Title: 239Pu(n,2n) 238Pu cross section inferred from IDA calculations and GEANIE measurements

Abstract

This report presents the latest {sup 239}Pu(n,2n){sup 238}Pu cross sections inferred from calculations performed with the nuclear reaction-modeling code system, IDA, coupled with experimental measurements of partial {gamma}-ray cross sections for incident neutron energies ranging from 5.68 to 17.18 MeV. It is found that the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section peaks at E{sub inc} {approx} 11.4 MeV with a peak value of approximately 326 mb. At E{sub inc} {approx} 14 MeV, the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section is found to be in good agreement with previous radio-chemical measurements by Lockheed. However, the shape of the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section differs significantly from previous evaluations of ENDL, ENDF/B-V and ENDF/B-VI. In our calculations, direct, preequilibrium, and compound reactions are included. Also considered in the modeling are fission and {gamma}-cascade processes in addition to particle emission. The main components of physics adopted and the parameters used in our calculations are discussed. Good agreement of the inferred {sup 239}Pu(n,2n){sup 238}Pu cross sections derived separately from IDA and GNASH calculations is shown. The two inferences provide an estimate of variations in the deduced {sup 239}Pu(n,2n){sup 238}Pu cross section originating from modeling.

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15006166
Report Number(s):
UCRL-ID-141663
TRN: US0400442
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Sep 2000
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; CROSS SECTIONS; FISSION; NEUTRONS; PHYSICS; SHAPE; SIMULATION

Citation Formats

Chen, H, Ormand, W E, and Dietrich, F S. 239Pu(n,2n) 238Pu cross section inferred from IDA calculations and GEANIE measurements. United States: N. p., 2000. Web. doi:10.2172/15006166.
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Chen, H, Ormand, W E, & Dietrich, F S. 239Pu(n,2n) 238Pu cross section inferred from IDA calculations and GEANIE measurements. United States. doi:10.2172/15006166.
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Chen, H, Ormand, W E, and Dietrich, F S. Fri . "239Pu(n,2n) 238Pu cross section inferred from IDA calculations and GEANIE measurements". United States. doi:10.2172/15006166. https://www.osti.gov/servlets/purl/15006166.
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@article{osti_15006166,
title = {239Pu(n,2n) 238Pu cross section inferred from IDA calculations and GEANIE measurements},
author = {Chen, H and Ormand, W E and Dietrich, F S},
abstractNote = {This report presents the latest {sup 239}Pu(n,2n){sup 238}Pu cross sections inferred from calculations performed with the nuclear reaction-modeling code system, IDA, coupled with experimental measurements of partial {gamma}-ray cross sections for incident neutron energies ranging from 5.68 to 17.18 MeV. It is found that the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section peaks at E{sub inc} {approx} 11.4 MeV with a peak value of approximately 326 mb. At E{sub inc} {approx} 14 MeV, the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section is found to be in good agreement with previous radio-chemical measurements by Lockheed. However, the shape of the inferred {sup 239}Pu(n,2n){sup 238}Pu cross section differs significantly from previous evaluations of ENDL, ENDF/B-V and ENDF/B-VI. In our calculations, direct, preequilibrium, and compound reactions are included. Also considered in the modeling are fission and {gamma}-cascade processes in addition to particle emission. The main components of physics adopted and the parameters used in our calculations are discussed. Good agreement of the inferred {sup 239}Pu(n,2n){sup 238}Pu cross sections derived separately from IDA and GNASH calculations is shown. The two inferences provide an estimate of variations in the deduced {sup 239}Pu(n,2n){sup 238}Pu cross section originating from modeling.},
doi = {10.2172/15006166},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Sep 01 00:00:00 EDT 2000},
month = {Fri Sep 01 00:00:00 EDT 2000}
}
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DOI:  10.2172/15006166
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    The goal of this project was to develop a new approach to measuring (n,2n) reactions for isotopes of interest. We set out to measure the 239Pu(n,2n) and 241Pu(n,2n) cross sections by directly detecting the 2n neutrons that are emitted. With the goal of improving the 239Pu(n,2n) cross section and to measure the 241Pu(n,2n) cross section for the first time. To that end, we have constructed a new neutron-charged-particle detector array called NeutronSTARS. It has been described extensively in Casperson et al. [1] and in Akindele et al. [2]. We have used this new neutron-charged-particle array to measure the 241Pu andmore » 239Pu fission neutron multiplicity as a function of equivalent incident-neutron energy from 100 keV to 20 MeV. We have made a preliminary determination of the 239Pu(n,2n) and 241Pu(n,2n) cross sections from the surrogate 240Pu(α,α’2n) and 242Pu(α,α’2n) reactions respectively. The experimental approach, detector array, data analysis, and results to date are summarized in the following sections.« less

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    The primary motivation for the present work is to provide theoretical values for the ratio of the partial 239Pu(n,2nx{gamma}) 238Pu to total 239 Pu(n,2n) 238Pu cross section for several discrete gamma transitions. Results and conclusions of preliminary calculations from threshold to 20 MeV are presented. Calculations are based on theoretical models with parameters obtained from the literature or from our ad hoc systematics. Optical model cross sections and transmission coefficients were determined using the coupled-channels method. The calculations included a preequilibrium component followed by multiple particle and gamma-ray emissions. Fission competition was included at all stages of de-excitation. Suggestions formore » further verifications and possible improvements are provided.« less

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  • ;
    The {sup 239}Pu(n,2n) and the {sup 235}U(n,2n) cross section are estimated by applying unitarity in several approaches: a subtraction method and also by using a ratio approach that relates the above cross sections to the {sup 238}U(n,2n) cross section and the {sup 239}Pu(n,2n) cross section to the {sup 235}U(n,2n) cross section, respectively. Also, a self-consistent, simultaneous analysis of the cross section data of four nuclei, {sup 239}Pu, {sup 235}U, {sup 238}U and {sup 232}Th, was undertaken to evaluate the {sup 239}Pu(n,2n) cross section at 11 MeV.

  • ; ; ; ...
    Using existing experimental data for neutron-induced total, elastic, inelastic, reaction and fission cross sections, as well as results from nuclear model calculations and evaluations from nuclear reaction data libraries, we derived an estimate for the cross sections for the {sup 235}U(n,2n) and {sup 239}Pu(n,2n) reactions for the neutron energy range from threshold to approximately 12 MeV. In effect, our approach is based on subtracting the fission and inelastic cross sections from the total reaction cross section where the difference is expected to yield the (n,2n) cross section. In addition to this subtraction approach, a ratio method and a differential methodmore » have also been explored. For {sup 235}U(n,2n), as a test case, we arrive at a cross section consistent with previous measurements, and for {sup 239}Pu(n,2n) we obtain a peak value of 400 {+-} 60 mb for the incident neutron energy range of 10 {le} E{sub n} {le} 12 MeV.« less