K isomerism in Rf255 and total kinetic energy measurements for spontaneous fission of Rf255,256,258

Abstract

Spontaneous fission properties of the isotopes $^{255}\mathrm{Rf}$, $^{256}\mathrm{Rf}$, and $^{258}\mathrm{Rf}$ produced in the reactions $^{50}\mathrm{Ti}+^{207}\mathrm{Pb}$, $^{50}\mathrm{Ti}+^{208}\mathrm{Pb}$, and $^{50}\mathrm{Ti}+^{209}\mathrm{Bi}$ were studied. The method of time and position correlations was used to identify spontaneous fission events. The correction to the energy deficit in measured total kinetic energy (TKE) determined on the basis of a study of $^{252}\mathrm{No}$ was applied to evaluate the $\overline{\mathrm{TKE}}$ of investigated rutherfordium isotopes. A signature which we assigned tentatively to bimodal fission was observed in TKE distributions of $^{255}\mathrm{Rf}$ and $^{256}\mathrm{Rf}$. Two new high-K isomeric states in $^{255}\mathrm{Rf}$ were identified by ER-CE-(CE)-$\ensuremath{\alpha}$/SF correlation search, with half-lives of ${38}_{\ensuremath{-}7}^{+12}$ and ${15}_{\ensuremath{-}4}^{+6}$ $\ensuremath{\mu}\mathrm{s}$ at excitation energies 1150--1450 and 900--1200 keV, respectively. Including those metastable states a tentative partial level scheme was proposed.