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Effects of the nuclear structure of fission fragments on the high-energy prompt fission $$gamma$$-ray spectrum in $$^{235}$$U($$n_{rm th},f$$)

$$^{235}$$U中性子誘起核分裂における高エネルギー$$gamma$$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.; L$'e$guillon, R.; 小川 達彦; Soldner, T.*; K$"o$ster, U.*; Pollitt, A.*; Hambsch, F.-J.*; Tsekhanovich, I.*; A$"i$che, 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.; L$'e$guillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; K$"o$ster, U.*; Pollitt, A.*; Hambsch, F.-J.*; Tsekhanovich, I.*; A$"i$che, 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 $$gamma$$-ray energy spectrum for cold-neutron induced fission of $$^{235}$$U was measured in the energy range $$E_{rm gamma}$$ = 0.8 - 20,MeV, by gaining a factor of about 10$$^{5}$$ in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at $$E_{rm gamma}approx$$4,MeV and $$approx$$6,MeV, and also a broad one at $$approx$$15,MeV. In order to understand the origins of these bumps, the $$gamma$$-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 $$approx$$4,MeV is created by the transitions between the discrete levels in the fragments around $$^{132}$$Sn, and the bump at $$approx$$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 $$E_{rm gamma}approx$$15,MeV, induced by the transition feeding into the low-lying high-spin states.

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