Future research program on prompt gamma-ray emission in nuclear fission
In recent years the measurement of prompt fission gamma-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions U-235(n(th), f), Pu-239(n(th), f) and Cf-252(sf). The renaissance was initiated by requests for new values especially for.-ray multiplicity and average total energy release per fission in neutron-induced fission of U-235 and Pu-239. 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 U-235 and Pu-241 as well as for the spontaneous fission of Cf-252 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 U-238, which is largely present in the fuel, or from gamma-induced fission from neutron capture in the construction material. A first experiment campaign on prompt gamma-ray emission from fast-neutron-induced fission on U-235,U-238 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.