Prompt $\gamma$-ray characteristics from $^{235}$U(n, f) at ${\overline{E}}_{n}$ = 1.7 MeV

Abstract

In response to nuclear data requests by OECD NEA, we present here the first results with respect to prompt-fission $\gamma$-ray spectra characteristics for fast neutrons on $^{235}$U. For that we have analyzed previously taken prompt-fission $\gamma$-ray data from the reaction $^{235}$U(n, f) induced by fast neutrons of average energy ${\overline{E}}_{n}$ = 1.7 MeV and spectral properties were deduced. It was expected that the values would be somewhat higher than for thermal-neutron induced fission of the same system, which at a first glance turned out to be not the case. However, taking the different prompt time windows relative to the coincidence timing resolution between both measurements into account, this discrepancy could be resolved. The results are an average multiplicity ${\overline{M}}_{\gamma }$ = 7.45 ± 0.48 $\gamma$ rays per fission and an average total $\gamma$-ray energy release in fission ${\overline{E}}_{\gamma ,tot}$ = (6.03 ± 0.47) MeV, which includes an additional relative uncertainty of 4% from the time window correction. The corresponding average energy per $\gamma$ ray is ${\overline{\epsilon }}_{\gamma }$ = (0.81 ± 0.04) MeV.