isomer shift

Isomer Shift and Magnetic Moment of the Long-Lived ½⁺ Isomer in ⁷⁹Zn: Signature of Shape Coexistence near ⁷⁸Ni

X.F. Yang et al.

doi: 10.1103/PhysRevLett.116.182502

Collinear laser spectroscopy is performed on the ⁷⁹Zn isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life is confirmed, and the nuclear spins and moments of the ground and isomeric states in ⁷⁹Zn, as well as the isomer shift are measured. From the observed hyperfine structures, spins I=9/2 and I=½ are firmly assigned to the ground and isomeric states. The magnetic moment μ(⁷⁹Zn)=-1.1866(10)μ_N, confirms the spin-parity I=9/2⁺ with a νg_9/2^-1  shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment μ(^79mZn)=-1.0180(12)μ_N  supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the N=50 shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state, δ2>^79,79m=+0.204(6) fm², providing first evidence of shape coexistence.