New K isomers in 248Cf

The nuclear structure of 248Cf was investigated at the Tokai Tandem Accelerator Laboratory of the Japan Atomic Energy Agency. 248Cf was one of the nuclei produced in the 18O +249Cf multinucleon transfer reaction. An array of Ge and LaBr3 detectors was used to detect the gamma rays emitted. More than ten new gamma-ray transitions from 248Cf were observed and, for the first time, lifetimes of excited states in the nanosecond range were measured. For the previously known bandhead of the 2- octupole vibrational band at 592 keV, a lifetime of 6.7(2) ns was found. Another, new isomeric state, with a lifetime of 16.8(5) ns, decays via a 48-keV E1 transition to a much longer-lived state lying at 0.9(3) MeV, for which a lifetime larger than approximate to 200 ns is estimated. For this latter state, the unobserved decay points to K ? 5. Considering available theoretical models, possible spin-parity assignments of new states are discussed.