Spectroscopy of Short-Lived Fission Fragment Isomers*

Fission is a well-known mechanism to populate excited states in neutron-rich isotopes. Fission is also an effective tool for studying isomeric decays, as they are often well-populated and relatively easy to detect. Isomeric states with half-lives in the $\sim $5 -- 100 $\mu $s range were examined using $^{6}$Li-induced fission on $^{232}$Th. A 45-MeV $^{6}$Li beam from the 88-Inch Cyclotron of LBNL was alternately blocked to provide beam on/off periods to populate and observe the isomeric decays. Fission fragments were tagged using a thin Si detector near the $^{232}$Th target, and coincident gamma rays were detected using six clover and one LEPS HPGe detectors of the LiBerACE array. Several isomers were identified in the A$\sim $95 and A$\sim $140 mass regions, as expected. Numerous isomers were also observed near A$\sim $120, due to the significant contribution from symmetric fission. Characteristics of the induced fission, with observed isomer populations and decays, will be discussed.