Nuclear isomerism

High-spin isomers have been searched for the nuclei in A=150 region by using heavy ion beams at RIKEN and JAERI. A series of isomers were found in N=83 isotones, 144Pm, 145Sm and 146Eu. Their excitation energies are all about 8.5 MeV. The half lives of these isomers are >2 μs(144Pm), 0.96 μs(145Sm) and 10 ns(146Eu), respectively. They turned out to be high-spin shape isomers whose decays may be understood by the barrier penetration which was used to interpret decays of fission isomers and recently found highly mixed K-isomers in A=180 region. (author)