Reexamining the role of the ( n,γf ) process in the low-energy fission of U235 and Pu239

Lynn, J. E.; Talou, P.; Bouland, O.

doi:10.1103/PhysRevC.97.064601

Title: Reexamining the role of the ( $n, γ f$ ) process in the low-energy fission of ${}^{235}U$ and ${}^{239}{Pu}$

Abstract

In this paper, the $$(n,{\gamma}f)$$ process is reviewed in light of modern nuclear reaction calculations in both slow and fast neutron-induced fission reactions on $$^{235}\mathrm{U}$$ and $$^{239}\mathrm{Pu}$$. Observed fluctuations of the average prompt fission neutron multiplicity and average total $${\gamma}$$-ray energy below 100-eV incident neutron energy are interpreted in this framework. The surprisingly large contribution of the $M1$ transitions to the prefission $${\gamma}$$-ray spectrum of $$^{239}\mathrm{Pu}$$ is explained by the dominant fission probabilities of $${0}^{+}$$ and $${2}^{+}$$ transition states, which can only be accessed from compound nucleus states formed by the interaction of $$s$$-wave neutrons with the target nucleus in its ground state, and decaying through $M1$ transitions. The impact of an additional low-lying $M1$ scissors mode in the photon strength function is analyzed. We review experimental evidence for fission fragment mass and kinetic-energy fluctuations in the resonance region and their importance in the interpretation of experimental data on prompt neutron data in this region. In conclusion, calculations are extended to the fast energy range where $$(n,{\gamma}f)$$ corrections can account for up to 3% of the total fission cross section and about 20% of the capture cross section.

Authors:

Lynn, J. E. ^[1]; Talou, P. ^[1]; Bouland, O. ^[2]

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Alternative Energies and Atomic Energy Commission (CEA), Saint-Paul-lez-Durance (France). Physics Studies Lab.

Publication Date:: 2018-06-01

Research Org.:: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:: USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:: 1441321

Alternate Identifier(s):: OSTI ID: 1439903

Report Number(s):: LA-UR-17-31364
Journal ID: ISSN 2469-9985; TRN: US1900899

Grant/Contract Number:: AC52-06NA25396

Resource Type:: Accepted Manuscript

Journal Name:: Physical Review C

Additional Journal Information:: Journal Volume: 97; Journal Issue: 6; Journal ID: ISSN 2469-9985

Publisher:: American Physical Society (APS)

Country of Publication:: United States

Language:: English

Subject:: 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; electromagnetic transitions; fission; nuclear reactions

Citation Formats


                    Lynn, J. E., Talou, P., and Bouland, O. Reexamining the role of the ( n,γf ) process in the low-energy fission of U235 and Pu239.  United States: N. p., 2018. 
Web.  doi:10.1103/PhysRevC.97.064601.

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                    Lynn, J. E., Talou, P., & Bouland, O. Reexamining the role of the ( n,γf ) process in the low-energy fission of U235 and Pu239.  United States.  https://doi.org/10.1103/PhysRevC.97.064601

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                    Lynn, J. E., Talou, P., and Bouland, O. Fri .  
"Reexamining the role of the ( n,γf ) process in the low-energy fission of U235 and Pu239".  United States.  https://doi.org/10.1103/PhysRevC.97.064601.  https://www.osti.gov/servlets/purl/1441321.

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@article{osti_1441321,

  title        = {Reexamining the role of the ( n,γf ) process in the low-energy fission of U235 and Pu239},

  author       = {Lynn, J. E. and Talou, P. and Bouland, O.},

  abstractNote = {In this paper, the $(n,{\gamma}f)$ process is reviewed in light of modern nuclear reaction calculations in both slow and fast neutron-induced fission reactions on $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$. Observed fluctuations of the average prompt fission neutron multiplicity and average total ${\gamma}$-ray energy below 100-eV incident neutron energy are interpreted in this framework. The surprisingly large contribution of the $M1$ transitions to the prefission ${\gamma}$-ray spectrum of $^{239}\mathrm{Pu}$ is explained by the dominant fission probabilities of ${0}^{+}$ and ${2}^{+}$ transition states, which can only be accessed from compound nucleus states formed by the interaction of $s$-wave neutrons with the target nucleus in its ground state, and decaying through $M1$ transitions. The impact of an additional low-lying $M1$ scissors mode in the photon strength function is analyzed. We review experimental evidence for fission fragment mass and kinetic-energy fluctuations in the resonance region and their importance in the interpretation of experimental data on prompt neutron data in this region. In conclusion, calculations are extended to the fast energy range where $(n,{\gamma}f)$ corrections can account for up to 3% of the total fission cross section and about 20% of the capture cross section.},

  doi          = {10.1103/PhysRevC.97.064601},

  journal      = {Physical Review C},

  number       = 6,

  volume       = 97,

  place        = {United States},

  year         = {2018},

  month        = {6}

}

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Works referenced in this record:

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Title: Reexamining the role of the ( n , γ f ) process in the low-energy fission of U 235 and Pu 239

Abstract

Citation Formats

Evidence for the Slow-Neutron Gamma-Fission Reaction in Pu 238 journal, January 1967

Cross section and γ -ray spectra for U 238 ( n , γ ) measured with the DANCE detector array at the Los Alamos Neutron Science Center journal, March 2014

Prompt fission neutrons from eV resonances in U 235 : Measurement and correlation with other fission properties journal, January 1976

Properties of prompt-fission γ rays journal, August 2014

R -matrix analysis and prediction of low-energy neutron-induced fission cross sections for a range of Pu isotopes journal, November 2013

Table of Superdeformed Nuclear Bands and Fission Isomers journal, October 2002

On the slow neutron, gamma-fission reaction journal, August 1965

Estimation of M 1 scissors mode strength for deformed nuclei in the medium- to heavy-mass region by statistical Hauser-Feshbach model calculations journal, August 2017

Channel analysis of cross sections and angular distributions for fission induced by neutrons and photons journal, September 1967

Quantification of Uncertainties for Evaluated Neutron-Induced Reactions on Actinides in the Fast Energy Range journal, December 2011

Spin determination of resonance structure in ( U 235 + n ) below 25 keV journal, September 1978

The (n, γf) process journal, February 1965

γ-Ray multiplicity in 239Pu fission induced by resonance neutrons: experimental evidence for the (n, γf) reaction journal, December 1973

International Evaluation of Neutron Cross Section Standards journal, December 2009

ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology journal, December 2006

Prompt neutron and gamma-ray yields in fission induced in 239Pu by resonance neutrons: Existence of the (n, γf) reaction journal, December 1972

The double-humped fission barrier journal, October 1980

Fission-neutron multiplicity and total prompt gamma-ray energy for resonances in Pu 239 journal, October 1974

Scissors resonance in the quasicontinuum of Th, Pa, and U isotopes journal, January 2014

Character and prevalence of third minima in actinide fission barriers journal, May 2013

Fission Studies of Thorium, Uranium, and Plutonium Isotopes with ( t , pf ) Reactions journal, December 1970

Prompt Fission Neutron Spectra of Actinides journal, January 2016

Measurements of the Energy Dependence of Prompt Neutron Emission from 233 U, 235 U, 239 Pu, and 241 Pu for E n = 0.005 to 10 eV Relative to Emission from Spontaneous Fission of 252 Cf journal, August 1984

Constraining the calculation of U 234 , 236 , 238 ( n , γ ) cross sections with measurements of the γ -ray spectra at the DANCE facility journal, August 2017

Fission of U, Np, Pu and Am isotopes excited in the (d, p) reaction journal, April 1971

Fission mode fluctuations in the resonances of 235U(n,f) journal, January 1989

Evaluation of p for 239 Pu: Impact for Applications of the Fluctuations at Low Energy journal, August 1988

Observation of Large Scissors Resonance Strength in Actinides journal, October 2012

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Title: Reexamining the role of the ( $n, γ f$ ) process in the low-energy fission of ${}^{235}U$ and ${}^{239}{Pu}$

Evidence for the Slow-Neutron Gamma-Fission Reaction in ${Pu}^{238}$
journal, January 1967

Cross section and $γ$ -ray spectra for ${}^{238}U$ ( $n$ , $γ$ ) measured with the DANCE detector array at the Los Alamos Neutron Science Center
journal, March 2014

Prompt fission neutrons from eV resonances in ${}^{235}U$ : Measurement and correlation with other fission properties
journal, January 1976

Properties of prompt-fission $γ$ rays
journal, August 2014

$R$ -matrix analysis and prediction of low-energy neutron-induced fission cross sections for a range of Pu isotopes
journal, November 2013

Table of Superdeformed Nuclear Bands and Fission Isomers
journal, October 2002

On the slow neutron, gamma-fission reaction
journal, August 1965

Estimation of $M 1$ scissors mode strength for deformed nuclei in the medium- to heavy-mass region by statistical Hauser-Feshbach model calculations
journal, August 2017

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journal, September 1967

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journal, December 2011

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journal, September 1978

The (n, γf) process
journal, February 1965

γ-Ray multiplicity in 239Pu fission induced by resonance neutrons: experimental evidence for the (n, γf) reaction
journal, December 1973

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Prompt neutron and gamma-ray yields in fission induced in 239Pu by resonance neutrons: Existence of the (n, γf) reaction
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The double-humped fission barrier
journal, October 1980

Fission-neutron multiplicity and total prompt gamma-ray energy for resonances in ${}^{239}{Pu}$
journal, October 1974

Scissors resonance in the quasicontinuum of Th, Pa, and U isotopes
journal, January 2014

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journal, May 2013

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Prompt Fission Neutron Spectra of Actinides
journal, January 2016

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journal, August 1984

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Fission mode fluctuations in the resonances of 235U(n,f)
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Observation of Large Scissors Resonance Strength in Actinides
journal, October 2012

Test of gamma-ray strength functions in nuclear reaction model calculations
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