  The radiative lifetime of the $A$ $^2 \Pi_{1/2}$ (v=0) state in radium
monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and
the related decay rate $\Gamma = 2.86(8) \times 10^7$ $s^{-1}$ are of relevance
to the laser cooling of RaF via the optically closed $A$ $^2 \Pi_{1/2}
\leftarrow X$ $^2\Sigma_{1/2}$ transition, which makes the molecule a promising
probe to search for new physics. RaF is found to have a comparable
photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to
its highly diagonal Franck-Condon matrix, it is expected to scatter an order of
magnitude more photons than other molecules when using just 3 cooling lasers,
before it decays to a dark state. The lifetime measurement in RaF is
benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3)
ns, in agreement with literature.
