The Alpha-Branching of AcK and the Presence of Astatine in Nature

Making use of the predictions of "alpha-systematics" on the extent of alpha-branching of the isotope AcK and of the properties of the resultant ${\mathrm{At}}^{219}$ daughter, the branching was looked for and found in the francium fraction isolated from a 20-mC source of ${\mathrm{Ac}}^{227}$. The observed branching rate is $\mathrm{ca}$ 4×${10}^{-5\mathrm{}}$, and the ${\mathrm{At}}^{219}$ daughter decays predominately by the emission of 6.27-Mev alpha-particles with a half-life of 0.9 minute to the new isotope ${\mathrm{Bi}}^{215}$, which in turn emits ${\beta }^{-}$ particles with a half-life of 8 minutes. ${\mathrm{At}}^{219}$ also decays by ${\beta }^{-}$ emission to ${\mathrm{An}}^{219}$ about once in 30 disintegrations. It is pointed out that this is the first reported instance of a chemical identification of an isotope of element 85 from a natural source, although other shorter-lived astatine isotopes are known to exist.