The Evolution of Nuclear Structure in Odd-A Zinc Isotopes

The hyperfine spectra of odd-A Zn (Z = 30) isotopes from N = 33 − 49 have been mea- sured using collinear laser spectroscopy at the COLLAPS (COLlinear LAser sPectroScopy) experiment at ISOLDE, CERN. From the hyperfine spectra, nuclear spins I, magnetic dipole moments µ and spectroscopic quadrupole moments Qs were determined across the Zn isotope chain, with isotopes ranging from stability to neutron-rich nuclei approaching N = 50. The 4s4p 3P2o → 4s5s 3S1 atomic transition was probed using a CW laser tuned to 481.1873 nm wavelength, and allowed for maximal sensitivity to the nuclear spin in order to unam- biguously confirm the ground and isomeric state spins of 73−79Zn. The nuclear moments of Zn isotopes were determined using the reference isotope 67Zn and the hyperfine coeffi- cients A(3P2) = +531.987(5) MHz and B(3P2) = +35.806(5) MHz, and reference moments µ = +0.875479(9)µN and Qs = +0.122(10) b, the latter of which is introduced in this work based on new electric field gradient (EFG) calculations. The nuclear moments are compared to predictions from large-scale shell model calculations in the f5pg9 (JUN45 and jj44b) and pfg9d5 (A3DA-m and LNPS-m) model spaces. The improvement of magnetic dipole moment predictions from JUN45 over those from A3DA-m and LNPS-m as N = 50 is approached points to the persistence of the N = 50 shell gap in neutron-rich Zn isotopes. Regarding quadrupole moments, the close agreement between measured Qs values and A3DA-m predictions beyond N = 40 highlights the importance of the νd5/2 orbital for characterising quadrupole deformation. The hyperfine structure of the newly-discovered isomer in 79Zn with tentatively assigned spin-parity of Iπ = 1/2+ has been directly observed for the first time in this work. In order to reproduce its measured nuclear properties, a novel interaction with an extended model space, PFSDG-U, is developed to understand the contributions to the nuclear wave function from np-mh excitations across the N = 50 shell closure.