Francium
Francium-223 is the most stable isotope, with a half-life of 21.8 minutes. Francium-223 is the fifth product of the actinium decay series as the daughter isotope of actinium-227. Francium-223 then decays into radium-223 by beta decay (1.149 MeV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).