Lifetime measurements of the7plevels of atomic francium

We present lifetime measurements of the ${7p}^2{P}_{3/2}$ and ${7p}^2{P}_{1/2}$ levels of Fr. We use a time-correlated single-photon counting technique on a cold sample of ${}^{210}\mathrm{Fr}$ atoms in a magneto-optic trap. We excite the atoms with the trapping and repumping beams of the magneto-optic trap and detect the decay of the atomic fluorescence. The results are a precision experimental test of the atomic many-body perturbation theory applied to the heaviest alkali metal. The lifetime results are 21.02(11) ns and 29.45(11) ns for the ${7p}^2{P}_{3/2}$ and ${7p}^2{P}_{1/2}$ levels, respectively. This gives a line strength ratio ${\mathcal{S}}_{1/2}$/${\mathcal{S}}_{3/2}$ of 0.526(3) for these levels in Fr. To study sources of systematic errors we measure the lifetimes of ${5p}^2{P}_{3/2}$ and ${5p}^2{P}_{1/2}$ in stable ${}^{87}\mathrm{Rb}$ and obtain 26.20(9) ns and 27.64(4) ns, respectively.