Collinear laser spectroscopy was performed on the nuclear ground states of the neutron-deficient isotopes ${}^{206,205,204}\mathrm{Fr}$. A new technique was developed to suppress hyperfine pumping in collinear laser spectroscopy of atoms. This involved high-frequency intensity modulation of narrow-linewidth laser light using fast-switching electro-optical modulators. The nuclear ground-state spins of ${}^{206,205,204}\mathrm{Fr}$ were determined to be 3, $9/2$, and 3, respectively. Both the changes in mean-squared charge radii and nuclear magnetic dipole moments indicate a departure from single-particle estimates.

• Received 8 June 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.122501