title: Isomers in 128Pd and 126Pd: evidence for a robust shell closure at the neutron magic number 82 in exotic palladium isotopes.
abstract: The level structures of the very neutron-rich nuclei 128Pd and 126Pd have been investigated for the first time. In the r-process waiting-point nucleus 128Pd, a new isomer with a half-life of 5.8(8) μs is proposed to have a spin and parity of 8(+) and is associated with a maximally aligned configuration arising from the g(9/2) proton subshell with seniority υ=2. For 126Pd, two new isomers have been identified with half-lives of 0.33(4) and 0.44(3) μs. The yrast 2(+) energy is much higher in 128Pd than in 126Pd, while the level sequence below the 8(+) isomer in 128Pd is similar to that in the N=82 isotone 130Cd. The electric quadrupole transition that depopulates the 8(+) isomer in 128Pd is more hindered than the corresponding transition in 130Cd, as expected in the seniority scheme for a semimagic, spherical nucleus. These experimental findings indicate that the shell closure at the neutron number N=82 is fairly robust in the neutron-rich Pd isotopes.
authors.affiliation: International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191, China and School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China and RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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