Measurement of diffusion coefficients of francium and rubidium in yttrium based on laser spectroscopy

We report the measurement of the diffusion coefficients of francium and rubidium ions implanted in a yttrium foil. We developed a methodology, based on laser spectroscopy, which can be applied to radioactive and stable species, and allows us to directly take record of the diffusion time. Francium isotopes are produced via fusion-evaporation nuclear reaction of a $^{18}\mathrm{O}$ beam on a Au target at the Tandem XTU accelerator facility in Legnaro, Italy. Francium is ionized at the gold-vacuum interface and ${\mathrm{Fr}}^{+}$ ions are then transported with an electrostatic beamline to a cell for neutralization and capture in a magneto-optical trap (MOT). A ${\mathrm{Rb}}^{+}$ beam is also available, which follows the same path as ${\mathrm{Fr}}^{+}$ ions. The accelerated ions are focused and implanted in an yttrium foil for neutralization. The time evolution of the MOT and the vapor fluorescence signals are used to determine diffusion times of Fr and Rb in Y as a function of temperature.