$7P_{1/2}$ hyperfine splitting in $^{206,207,209,213}$Fr and the hyperfine anomaly*

We perform precision measurements on francium, the heaviest alkali with no stable isotopes, at the recently commissioned Francium Trapping Facility at TRIUMF. A combination of RF and optical spectroscopy allows better than 10 ppm (statistical) measurements of the $7P_{1/2}$ state hyperfine splitting for the isotopes $^{206,207,209,213}$Fr, in preparation for weak interaction studies. Together with previous measurements of the ground state hyperfine structure, it is possible to extract the hyperfine anomaly. This is a correction to the point interaction of the nuclear magnetic moment and the electron wavefunction, known as the Bohr Weisskopf effect. Our measurements extend previous measurements\footnote{Grossman {\it et al} Phys. Rev. Lett. 83, 935 (1999).} to the neutron closed shell isotope (213) as well as further in the neutron deficient isotopes (206, 207).