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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

Journal Article · · Physical Review C
 [1];  [1];  [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Alternative Energies and Atomic Energy Commission (CEA), Saint-Paul-lez-Durance (France). Physics Studies Lab.

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.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1441321
Alternate ID(s):
OSTI ID: 1439903
Report Number(s):
LA-UR-17-31364; TRN: US1900899
Journal Information:
Physical Review C, Vol. 97, Issue 6; ISSN 2469-9985
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 10 works
Citation information provided by
Web of Science

References (29)

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
Test of gamma-ray strength functions in nuclear reaction model calculations journal May 1990