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

The half-lives of Fr-221, Ar-217, Bi-213, Po-213, and Pb-209 were measured by means of an ion-implanted planar Si detector for alpha and beta particles emitted from weak Ac-225 sources or from recoil sources, which were placed in a quasi-2 pi counting geometry. Recoil sources were prepared by collecting atoms from an open Ac-225 source onto a glass substrate. The Fr-221 and Bi-213 half-lives were determined by following the alpha particle emission rate of recoil sources as a function of time. Similarly, the Pb-209 half-life was determined from the beta particle count rate. The shorter half-lives of At-217 and Po-213 were deduced from delayed coincidence measurements on weak Ac-225 sources using digital data acquisition in list mode. The resulting values: T-1/2(Fr-221)=4.806 (6) min, T-1/2(At-217)=32.8 (3) ms, T-1/2(Bi-213)=45.62 (6) min, T-1/2(Po-213)=3.708 (8) mu s, and T-1/2(Pb-209)=3.232 (5) h were in agreement only with the best literature data. (C) 2013 Elsevier Ltd. All rights reserved.