<P> There are 34 known isotopes of francium ranging in atomic mass from 199 to 232 . Francium has seven metastable nuclear isomers . Francium - 223 and francium - 221 are the only isotopes that occur in nature, though the former is far more common . </P> <P> Francium - 223 is the most stable isotope, with a half - life of 21.8 minutes, and it is highly unlikely that an isotope of francium with a longer half - life will ever be discovered or synthesized . 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 (1149 keV decay energy), with a minor (0.006%) alpha decay path to astatine - 219 (5.4 MeV decay energy). </P> <P> Francium - 221 has a half - life of 4.8 minutes . It is the ninth product of the neptunium decay series as a daughter isotope of actinium - 225 . Francium - 221 then decays into astatine - 217 by alpha decay (6.457 MeV decay energy). </P> <P> The least stable ground state isotope is francium - 215, with a half - life of 0.12 μs: it undergoes a 9.54 MeV alpha decay to astatine - 211 . Its metastable isomer, francium - 215m, is less stable still, with a half - life of only 3.5 ns . </P>

In the alpha decay of francium-221 what daughter element is produced