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 [$t_{1/2}=22.0(5)\mathrm{ms}$] ${}^{219}\mathrm{Fr}$ $Q_s=-1.21(2)\mathrm{eb}$, 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.

• Received 24 June 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.132501

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Published by the American Physical Society