Measurement of high-energy prompt fission rays in U(n,f)

Ogawa, Tatsuhiko   ; Makii, Hiroyuki   ; Nishio, Katsuhisa   ; Hirose, Kentaro  ; Orlandi, R.  ; Lguillon, R.*; Soldner, T.*; Hambsch, F.-J.*; Ache, M.*; Astier, A.*; Czajkowski, S.*; Frost, R.*; Guo, S.*; Kster, U.*; Mathieu, L.*; Otsuki, Tsutomu*; Petrache, C. M.*; Pollitt, A.*; Sekimoto, Shun*; Takamiya, Koichi*; Tsekhanovich, I.*

Measurement of -rays emitted from fission of actinide has been conducted for radiation transport analysis in reactors, safety of spent fuel, and fundamental nuclear physics. In earlier studies, -rays up to 8 MeV were measured because they are those emitted by fission fragments at excited states. According to some theoretical studies, however, some fission fragments have excitation energy up to 20 MeV and they emit -rays above 8 MeV. In this study, the -rays produced by fission of U induced by thermal neutrons were measured with LaBr scintillators at the high-flux reactor in the Institut Laue Langevin. The obtained -ray spectrum agreed with the earlier measurement below 8 MeV, forms a bump above 10 MeV, and smoothly continued up to 20 MeV. The measurement in this study clarified the -ray energy spectrum attributed to fission reactions up to 20 MeV in case of U(n,f).