Nuclear structure of light thallium isotopes as deduced from laser spectroscopy on a fast atom beam

Refined theoretical values of field and mass isotope shifts in thallium to extract charge radii of Tl isotopes

Electronic factors for the field and mass isotope shifts in the 6p ²P_3/2 → 7s ²S_1/2 (535 nm), 6p ²P_1/2 → 6d ²D_3/2 (277 nm), and 6p ²P_1/2 → 7s ²S_1/2 (378 nm) transitions in neutral thallium were calculated within the high-order relativistic coupled cluster approach. These factors were used to reinterpret previous experimental isotope shift measurements in terms of charge radii of a wide range of Tl isotopes. Good agreement between theoretical and experimental King-plot parameters was found for the 6p ²P_3/2 → 7s ²S_1/2 and 6p ²P_1/2 → 6d ²D_3/2 transitions. It was shown that the value of the specific mass shift factor for the 6p ²P_3/2 → 7s ²S_1/2 transition is not negligible compared with the value of normal mass shift in contrast to what had been suggested previously. Theoretical uncertainties in the mean square charge radii were estimated. They were substantially reduced compared with the previously ascribed ones and amounted to less than 2.6%. The achieved accuracy paves the way for a more reliable comparison of the charge radii trends in the lead region.

Isomer Shift and Magnetic Moment of the Long-Lived 1/2^{+} Isomer in _{30}^{79}Zn_{49}: Signature of Shape Coexistence near ^{78}Ni

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.

New laser setup for the selective isotope production and investigation in a laser ion source at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility

New laser installation for the resonance ionization spectroscopy in a laser ion source and for rare isotope production has been recently put into operation at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility (Petersburg Nuclear Physics Institute, Gatchina). This is a significant improvement of a previous target-laser ion source device of the IRIS mass-separator, working on-line with 1 GeV proton beam of PNPI (Petersburg Nuclear Physics Institute) synchrocyclotron. It makes possible for us to get the isobarically clean radioactive isotope beams of a great number of chemical elements. New laser setup provides the two- or three-resonance step ionization in the range of wavelength of 265-850 nm. The first results obtained at the laser setup for Tl isotopes are presented.