Promptγspectroscopic studies of fragment nuclei in thermal neutron induced fission of235U

Abstract

The prompt $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence technique has been used to carry out the spectroscopic study of the level schemes and to derive the relative isotopic yield distributions of fission fragment nuclei employing the ${}^{235}$U(${n}_{th}$, $f$) reaction for the first time. From the coincidence rates of various Ba isotopes with ${}^{90}$Kr nucleus and of Sr isotopes with ${}^{138}$Xe nucleus, it has been found that either the $2n$ or $3n$ neutron evaporation channels dominate during the fission process. The average angular momenta for three complementary pairs have been estimated. The yrast and near-yrast level structures in several isotopes of six elements (Sr, Xe, Kr, Ba, Zr, and Te) have been deduced. The level schemes obtained are compared with earlier reported works, where different reactions or spontaneous fission (SF) data were used.