100 Years of Nuclear Isomers

Properties of deformed, neutron-rich nuclei in the A~110 and 160 mass regions are important for achieving better understanding of the nuclear structure where little is known owing to difficulties in the production of these nuclei at the present RIB facilities. They are essential ingredient in the interpretation of the r-process nucleosynthesis and are needed in fission-like applications since theoretical models depend sensitively on the nuclear structure input. Predicated on these ideas, we have initiated dedicated decay spectroscopy experimental program at Argonne National Laboratory, by combining the CARIBU radioactive beam facility with the newly developed Gammasphere decay station. The initial focus was on several deformed odd-odd nuclei, where ${\beta }^{-}$ decays of both the ground state and an excited isomer were investigated. Because of the spin difference, a variety of structures in the daughter nuclei were selectively populated and characterized, which in turn provided information about the structure of the isomers. Mass measurements using the Canadian Penning Trap aimed at discovering of long-lived isomers in these regions and at determining of their excitation energies were also carried out.

Results from these experiments will be presented and compared with predictions from multi-quasiparticle blocking calculations. The effects of K-forbiddenness on the ${\beta }^{-}$-decay strengths will also be discussed.
${}^{\ast }$ Work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 and the National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation R & D (NA-22).