Measurement of the 226Th and 222Ra half-lives.

The half-lives of 226Th and 222Ra were measured by counting alpha-particle emissions from sources as a function of time. The 226Th sources were prepared from an open 230U source, capturing recoil atoms after alpha-particle decay on glass disks or even directly onto a detector. Similarly, the 222Ra sources were obtained by self-transfer of recoil atoms from 226Th sources. The activity measurements were performed in (nearly-)2π geometry with an ion-implanted silicon detector. The decay curves were analysed in different ways, incl. moment analysis, trying to avoid the pitfalls of bias of least-squares fits to Poisson distributed data. The observed half-life values are T1/2(226Th)=30.70 (3) min and T1/2(222Ra)=33.6 (4) s. Literature values show some inconsistency.