Effects of the nuclear structure of fission fragments on the high-energy prompt fission -ray spectrum in U()
U中性子誘起核分裂における高エネルギー線スペクトルに対する核分裂片の核構造の影響
牧井 宏之 ; 西尾 勝久 ; 廣瀬 健太郎 ; Orlandi, R. ; Lguillon, R.; 小川 達彦 ; Soldner, T.*; Kster, U.*; Pollitt, A.*; Hambsch, F.-J.*; Tsekhanovich, I.*; Ache, M.*; Czajkowski, S.*; Mathieu, L.*; Petrache, C. M.*; Astier, A.*; Guo, S.*; 大槻 勤*; 関本 俊*; 高宮 幸一*; Frost, R. J. W.*; 河野 俊彦*
Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; Kster, U.*; Pollitt, A.*; Hambsch, F.-J.*; Tsekhanovich, I.*; Ache, M.*; Czajkowski, S.*; Mathieu, L.*; Petrache, C. M.*; Astier, A.*; Guo, S.*; Otsuki, Tsutomu*; Sekimoto, Shun*; Takamiya, Koichi*; Frost, R. J. W.*; Kawano, Toshihiko*
The prompt fission -ray energy spectrum for cold-neutron induced fission of U was measured in the energy range = 0.8 - 20,MeV, by gaining a factor of about 10 in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at 4,MeV and 6,MeV, and also a broad one at 15,MeV. In order to understand the origins of these bumps, the -ray spectra were calculated using a statistical Hauser-Feshbach model, taking into account the de-excitation of all the possible primary fission fragments. It is shown that the bump at 4,MeV is created by the transitions between the discrete levels in the fragments around Sn, and the bump at 6,MeV mostly comes from the complementary light fragments. It is also indicated that a limited number of nuclides, which have high-spin states at low excitation energies, can contribute to the bump structure around 15,MeV, induced by the transition feeding into the low-lying high-spin states.