Future research program on prompt $\gamma$ -ray emission in nuclear fission

Abstract

Abstract. In recent years the measurement of prompt fission γ-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions 235 U(n th , f), 239 Pu(n th , f) and 252 Cf(sf). The renaissance was initiated by requests for new values especially for γ-ray multiplicity and average total energy release per fission in neutron-induced fission of 235 U and 239 Pu. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on 235 U and 241 Pu as well as for the spontaneous fission of 252 Cf with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on 238 U, which is largely present in the fuel, or from γ-induced fission from neutron capture in the construction material. A first experiment campaign on prompt γ-ray emission from fast-neutron-induced fission on 235,238 U was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies.

Simultaneous measurement of neutron-induced fission and capture cross sections for 241Am at neutron energies below fission threshold

“…In the thermal-neutron fission of 239 Pu, for example, 6.9 γ rays per fission are emitted on average with an average energy of 1.0 MeV [20]. The average total γ-ray energy per fission, ∼ 7 MeV, was also obtained in more recent measurement for the spontaneous fission of 252 Cf and the thermal-neutron fission of 235 U, 241 Pu [21]. Considering that the fission cross section for 241 Am is two orders of magnitude smaller than the capture cross section [22] in the neutron energy region of this measurement (E n < 20 eV), γ rays detected in the scintillators are assumed to originate from the neutron capture process.…”

Neutron induced fission of 237Np – status, challenges and opportunities

“…New experiments can be conducted, e.g. at the high-resolution neutron time-of-flight facility GELINA [24], with a focus on measuring < ν n > and < ν γ >, prompt n/γ-ray competition, correlations r(<TKE>, Γ −1 f ) [21], n-and γ-yields as a function of resonance neutron energy. The assessment of those quantities in correlation with fission fragment properties (A, TKE), i.e.…”

“…To minimize the influence of the statistical and systematic uncertainties, new experiments need to be conducted on the different existing resonance-neutron TOF facilities [22][23][24], using fission fragment and multi n-γ detector spectrometers.…”

Nuclear fission: a review of experimental advances and phenomenology

“…A c c e p t e d M a n u s c r i p t servables, including prompt neutron [58,59] and γ-ray multiplicities [60,61,62,63]. We note that similar detection methods are also exploited in the SF and βDF studies, but some sort of preseparation (chemical or electromagnetic) of the fissioning parent nucleus is often used in such cases, see Sections 4.4 and 4.1.…”