Investigation of the structure of U(n,fission) prompt gamma energy spectrum by FIFRELIN

Ogawa, Tatsuhiko   ; Litaize, O.*; Mancusi, D.*; Chebboubi, A.*; Serot, O.*

Thermal fission of U-235 is fundamental for nuclear energy engineering, whose details were observed through neutrons and gamma-rays. Among them, gamma-rays above 8 MeV, which come from immediate gamma deexcitation of fission fragments, were recently measured as a probe to observe fission more directly. The energy spectrum measured by a theoretical model CoH3 (Coupled-Channels Hauser-Feshbach Code) reproduced a peak around 4 MeV and a shoulder from 6 to 8 MeV, however, underestimated the components above 14 MeV. In this study, we used FIFRELIN developed by the French Atomic Energy, Alternative Energy Commission (CEA) to reproduce the gamma-ray energy spectrum. In addition to the peak around 4 MeV and a shoulder from 6 to 8 MeV, gamma spectrum up to 20 MeV was reproduced. This calculation also discovered that the level-density model for fission fragments plays the critical role. It was thus illustrated that FIFRELIN is useful to reproduce the spectra of gamma-ray from fission and investigate the reaction processes responsible for gamma-ray spectrum.