Half-Life Determination Of Bi-213 And Pb-209 By Means Of Cherenkov Counting And Detection With A Nai Detector

An Ac-225 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 Bi-213 and Pb-209 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 Nat detector to detect gamma rays. The analysis of the data yielded an independent result for the half-life of Bi-213. Combining the results of both measurement techniques, T-1/2 (Bi-213) = (45.60 +/- 0.09) min was obtained as a final value for the half-life of Bi-213. The half-life of Pb-209 was found to be T-1/2(Pb-209) = (195.1 +/- 2.6) min.