Monopole-Driven Shell Evolution below the Doubly Magic Nucleus 132Sn Explored with the Long-Lived Isomer in 126Pd.

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in 126Pd and is proposed to have a spin and parity of 10+ with a maximally aligned configuration comprising two neutron holes in the 1h11/2 orbit. In addition to an internal-decay branch through a hindered electric octupole transition, β decay from the long-lived isomer was observed to populate excited states at high spins in 126Ag. The smaller energy difference between the 10+ and 7- isomers in 126Pd than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h11/2 neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below 132Sn are discussed in terms of the central and tensor forces. [ABSTRACT FROM AUTHOR]