Isomer Shift and Magnetic Moment of the Long-Lived1/2+Isomer inZn49

Abstract

Collinear laser spectroscopy is performed on the _{30}^{79}Zn_{49} 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 ^{79}Zn as well as the isomer shift are measured. From the observed hyperfine structures, spins I=9/2 and I=1/2 are firmly assigned to the ground and isomeric states. The magnetic moment μ (^{79}Zn)=-1.1866(10)μ_{N}, confirms the spin-parity 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 (^{79m}Zn)=-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, δ⟨r_{c}^{2}⟩^{79,79m}=+0.204(6) fm^{2}, providing first evidence of shape coexistence.

Investigating the large deformation of the 5/2+ isomeric state in Zn73 : An indicator for triaxiality

“…Three resonances were observed in a total measurement range of >5 GHz, confirming a nuclear spin of I = 1/2 for the ground state (T 1/2 = 23.5 s [31] with higher spin as proposed in [20] was not observed in the current spectrum, indicating that it does not exist or is not populated with this reaction in the target. However, since positive parity high-spin states in 69,71,75,77,79 Zn were easily observed under the same experimental conditions [18,19], we conclude that there is no evidence of a 5.8 s isomeric state in 73 Zn. To be able to observe any short-lived isomer and enhance the total production of 73 Zn, the 1.4-GeV proton beam was switched to impinge directly on the UC x target instead of a neutron converter.…”

“…The experiment was performed at the collinear laser spectroscopy (COLLAPS) setup [26] at CERN-ISOLDE, as detailed in earlier publications [18,19]. The Zn isotopes were produced by impinging 1.4-GeV protons onto a neutron converter [27] of a UC x target, laser resonantly ionized by the resonant ionization laser-ion source [28], and accelerated up to 30 keV.…”

“…Measurements of ground state properties from laser spectroscopy have also provided considerable nuclear structure information in this region [14][15][16][17][18][19]. With one proton above Z = 28, a study of Cu isotopes revealed a primarily single-particle nature and a weak "magic" behavior around N = 40 from the spins, moments, and charge radii, but also showed a nonnegligible contribution from NN correlations and cross-shell excitations [14,16,17].…”

Collinear laser spectroscopy at ISOLDE: new methods and highlights

“…Laser spectroscopy was also well-placed to confirm the existence of and firmly assign spins to long-lived isomeric states in the Zn isotopes. In particular an intruder isomeric state was established in 79m Zn [65], which notably displayed a signature of shape coexistence.  suggested the appearance of a new magic number at N=32 towards 52 Ca [79][80][81][82].…”

Search for the Ga73 ground-state doublet splitting in the β decay of Zn73

“…§ Deceased the role of polarization effects from the Z = 28 proton shell. Such stability has been recently challenged by experimental evidence that points towards the weakening of the N = 50 shell closure around 78 Ni and the coexistence of deformed low-lying intruder states with the normal configuration ground states [2][3][4][5].…”