Isomeric states in the semimagic ${}^{128-130}$Sn isotopes were populated in the fragmentation of a ${}^{136}\mathrm{Xe}$ beam on a ${}^9\mathrm{Be}$ target at an energy of 750 $A·$MeV. The decay of an isomeric state in ${}^{128}\mathrm{Sn}$ at an excitation energy of 4098 keV has been observed. Its half live has been determined to be $T_{1/2}=220(30)$ ns from the time distributions of the delayed $\gamma$ rays emitted in its decay. $\gamma \gamma$ coincidence relations were analyzed in order to establish the decay pattern of the newly established state toward the known (7${}^{-}$) and (10${}^{+}$) isomers at excitation energies of 2092 and 2492 keV, respectively. Based on a comparison with results of state-of-the-art shell-model calculations the new isomeric state is proposed to have the $\nu h_{11/2}^{-3}{d}_{3/2}^{-1}$ configuration with the four neutron holes in ${}^{132}\mathrm{Sn}$ maximally aligned to a total spin of $I^{\pi }={15}^{-}$.

• Received 5 November 2010

DOI:https://doi.org/10.1103/PhysRevC.83.044328