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The magnetic moments and isotope shifts of the neutron-deficient francium isotopes 202-205Fr were measured at ISOLDE-CERN with use of collinear resonance ionization spectroscopy. A production-to-detection efficiency of 1% was measured for 202Fr. The background from nonresonant and collisional ionization was maintained below one ion in 105 beam particles. Through a comparison of the measured charge radii with predictions from the spherical droplet model, it is concluded that the ground-state wave function remains spherical down to 205Fr, with a departure observed in 203Fr (N=116). [ABSTRACT FROM AUTHOR]

New technical developments have led to a 2 orders of magnitude improvement of the resolution of the collinear resonance ionization spectroscopy (CRIS) experiment at ISOLDE, CERN, without sacrificing the high efficiency of the CRIS technique. Experimental linewidths of 20(1) MHz were obtained on radioactive beams of francium, allowing us for the first time to determine the electric quadrupole moment of the short lived [t1/2 = 22.0(5) ms] 219Fr Qs = -1.21(2) eb, which would not have been possible without the advantages offered by the new method. This method relies on a continuous-wave laser and an external Pockels cell to produce narrow-band light pulses, required to reach the high resolution in two-step resonance ionization. Exotic nuclei produced at rates of a few hundred ions/s can now be studied with high resolution, allowing detailed studies of the anchor points for nuclear theories. [ABSTRACT FROM AUTHOR]

The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich 2l8m,2l9,229,23lFr isotopes were measured with the newly installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at the On-Line Isotope Mass Separator (ISOLDE), CERN, probing the 7s²S1/2 to 8p2 P3/2 atomic transition. The δ(r²)A-221 values for 218m,219Fr and 229,23lFr follow the observed increasing slope of the charge radii beyond N = 126. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that 220Fr has a weakly inverted odd-even staggering while 228Fr has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The g(2l9Fr) = +0.69 (1) value supports a π1h9/2 shell-model configuration for the ground state. The g(229,231Fr) values support the tentative Iπ(229,231Fr) = (l/2+) spin and point to a πS-11/2 intruder ground-state configuration. [ABSTRACT FROM AUTHOR]