Half-lives of 221Fr, 217At, 213Bi, 213Po and 209Pb from the 225Ac decay series.

The half-lives of 221Fr, 217At, 213Bi, 213Po, and 209Pb were measured by means of an ion-implanted planar Si detector for alpha and beta particles emitted from weak 225Ac sources or from recoil sources, which were placed in a quasi-2π counting geometry. Recoil sources were prepared by collecting atoms from an open 225Ac source onto a glass substrate. The 221Fr and 213Bi half-lives were determined by following the alpha particle emission rate of recoil sources as a function of time. Similarly, the 209Pb half-life was determined from the beta particle count rate. The shorter half-lives of 217At and 213Po were deduced from delayed coincidence measurements on weak 225Ac sources using digital data acquisition in list mode. The resulting values: T1/2(221Fr)=4.806 (6) min, T1/2(217At)=32.8 (3)ms, T1/2(213Bi)=45.62 (6)min, T1/2(213Po)=3.708 (8)μs, and T1/2(209Pb)=3.232 (5)h were in agreement only with the best literature data.