Isomer studies with RI-beam induced fusion reactions and in-flight fission reactions

Shape evolution is one of the most important subjects to disentangle competition between the single-particle and collective motions in the finite quantum many-body system. A drastic change of nuclear shapes sometimes causes isomers due to a very small transition probability between states with different nuclear structures. Therefore, the isomer is one of the effective probes to search for the change of nuclear structure. To investigate the shape evolution in the wider isospin and angular momentum region, we have performed two types of experiments based on the isomer spectroscopy. The one is the experiment by using the low-energy (around 5-10 MeV/u) RI-beam induced fusion reaction to search for isomers in the high-spin states of nuclei close to the β-stability line. The other is the experiment by using the in-flight fission reaction to search for isomers in the extremely neutron-rich exotic nuclei far from the β-stability line. These experimental methods and results are introduced and the nuclear structure of the observed isomers are discussed. (author)