Reexamining the role of the ( ) process in the low-energy fission of and
- 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.
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
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