The 1.9-s isomeric state (Rf261b) in Rf261 was directly populated in the Cm248(O18,5n)Rf261b reaction. Alpha and spontaneous fission (SF) decays of Rf261b, as well as the 68-s state Rf261a, was investigated with a rotating wheel apparatus under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. An identification of Rf261b was based on α-α correlations linking α decays of Rf261b and its daughter No257. The α-particle energy of Rf261b was measured to be 8.52 ± 0.05 MeV. The half-life was determined to be 1.9 ± 0.4 s based on both 8.52-MeV α and SF decays. The α and SF branches are 0.27±0.06 and 0.73±0.06, respectively. The cross section for the Cm248(O18,5n)Rf261b reaction is σ(Rf261b)=11±2 nb at 95.1 MeV, which gives a cross-section ratio of σ(Rf261a)/ σ(Rf261b)=1.1±0.2.
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