The spectroscopic electric quadrupole moment of the neutron-deficient francium isotope ${}^{203}\mathrm{Fr}$ was measured by using high-resolution collinear resonance ionization spectroscopy (CRIS) at the CERN Isotope Separation On-Line Device (ISOLDE) facility. A remeasurement of the ${}^{207}\mathrm{Fr}$ quadrupole moment was also performed, resulting in a departure from the established literature value. A sudden increase in magnitude of the ${}^{203}\mathrm{Fr}$ quadrupole moment, with respect to the general trend in the region, points to an onset of static deformation at $N=116$ in the ${}_{87}\mathrm{Fr}$ isotopic chain. Calculation of the static and total deformation parameters show that the increase in static deformation only cannot account for the observed departure of its relative charge radius from the ${}_{82}\mathrm{Pb}$ chain.

• Received 30 June 2017
• Revised 17 August 2017

DOI:https://doi.org/10.1103/PhysRevC.96.034317

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Published by the American Physical Society