Half-life determination of ²¹³Bi and ²⁰⁹Pb by means of Cherenkov counting and detection with a NaI detector

An ²²⁵Ac source was prepared and combined with a dedicated setup to collect recoil atoms which are ejected as a consequence of alpha decay. Some targets were made of acrylic glass and were then placed in custom-built triple-to-double coincidence ratio (TDCR) counters to measure the Cherenkov counting rates as a function of time. Half-lives of ²¹³Bi and ²⁰⁹Pb were derived from the data. In addition, polyethylene films were used as targets to collect recoil atoms. These films were then measured in a well-type NaI detector to detect gamma rays. The analysis of the data yielded an independent result for the half-life of ²¹³Bi. Combining the results of both measurement techniques, T_1/2(²¹³Bi) = (45.60 ± 0.09) min was obtained as a final value for the half-life of ²¹³Bi. The half-life of ²⁰⁹Pb was found to be T_1/2(²⁰⁹Pb) = (195.1 ± 2.6) min.