Late Time Emission of Prompt Fission Gamma Rays

Abstract

The emission of prompt fission $\gamma$ rays within a few nanoseconds to a few microseconds following the scission point is studied in the Hauser-Feshbach formalism applied to the deexcitation of primary excited fission fragments. Neutron and $\gamma$-ray evaporations from fully accelerated fission fragments are calculated in competition at each stage of the decay, and the role of isomers in the fission products, before $\beta$-decay, is analyzed. The time evolution of the average total $\gamma$-ray energy, average total $\gamma$-ray multiplicity, and fragment-specific $\gamma$-ray spectra, is presented in the case of neutron-induced fission reactions of ${}^{235}$U and ${}^{239}$Pu, as well as spontaneous fission of ${}^{252}$Cf. The production of specific isomeric states is calculated and compared to available experimental data. About 7% of all prompt fission $\gamma$ rays are predicted to be emitted between 10 nsec and 5 $\mu$sec following fission, in the case of ${}^{235}$U and ${}^{239}$Pu $(n_{\mathrm{th}},f)$ reactions, and up to 3% in the case of ${}^{252}$Cf spontaneous fission. The cumulative average total $\gamma$-ray energy increases by 2 to 5% in the same time interval. Finally, those results are shown to be robust against significant changes in the model input parameters.

arXiv comment11 pages, 14 figures

References in corpus (1)

• Nuclear ground-state masses and deformations: FRDM(2012)

Cited by in corpus (10)

• Review on the progress in nuclear fission
• Theory of Nuclear Fission
• Fission Fragment Decay Simulations with the CGMF Code
• Correlated Prompt Fission Data in Transport Simulations
• Hauser-Feshbach fission fragment de-excitation with calculated macroscopic-microscopic mass yields
• Improved modeling of photon observables with FREYA
• High resolution measurement of tagged two-neutron energy and angle correlations in Cf-252(sf)
• Energy dependence of the prompt $\gamma$-ray emission from the $(d,p)$-induced fission of ${}^{234}{\mathrm{U}}^{\ast }$ and ${}^{240}{\mathrm{Pu}}^{\ast }$
• Event-by-Event Multiplicity Correlations in ${}^{252}$Cf(sf)
• Consideration of memory of spin and parity in the fissioning compound nucleus by applying the Hauser-Feshbach fission fragment decay model to photonuclear reactions