A method for determining 212 Bi by TDCR Cherenkov counting

212 Bi is one of the potential medical alpha emitters for targeted alpha therapy, and development of a precise activity measurement method for 212 Bi is necessary. In this work, a triple-to-double coincidence ratio (TDCR) Cherenkov method for the measurement of 212 Bi activity was established. 224 Ra source, calibrated by alpha spectrometry, was utilized for the method development. Cherenkov radiation emitted from the progenies of 224 Ra was studied in details, demonstrating that 212 Bi and its daughter 208 Tl would dominate the production of Cherenkov photons while the contributions from 224 Ra, 220 Rn, 216 Po, 212 Pb and 212 Po can be negligible. Potential counting loss of 212 Pb and 212 Bi owing to the emanation of 220 Rn from the sample solution was also studied, and no obvious influence was obsevered. Thus, the TDCR Cherenkov quench curve was prepared using 224 Ra as a 212 Bi source. The performance of the method was examined using spiked samples with the 212 Bi activities varied from 1.69 to 91.31 Bq, and the measured results agreed well with the expected values. The minimum detectable activity was determined to be 0.21 Bq.