Determination of ²²³Ra Activity by TDCR Cherenkov Counting Technique

To address the requirement for accurate activity measurement of the medical α-emitting radionuclide ²²³Ra in radiopharmaceutical development and clinical application, this study established a triple-to-double coincidence ratio (TDCR) Cherenkov counting method for measuring ²²³Ra activity. In this work, a TDCR liquid scintillation counter was used to calibrate the activity of ²²³Ra. The Cherenkov spectra of ²²³Ra and the TDCR efficiency correction curve was obtained. The Cherenkov spectra, detection efficiencies, and the effects of color quenching between ²²³Ra and ²²⁴Ra were compared. The results showed that Cherenkov light originating from the daughter nuclides ²¹¹Pb and ²⁰⁷Tl can be used for accurate activity determination of ²²³Ra, with a maximum detection efficiency of up to 60% and a minimum detectable activity of 0.2 Bq. A good correlation was observed between TDCR values and the detection efficiency of ²²³Ra, enabling efficiency correction in activity measurements. The TDCR Cherenkov counting method exhibited similar detection efficiencies for ²²³Ra and ²²⁴Ra, whereas color quenching affected ²²³Ra more significantly. This study demonstrated that TDCR Cherenkov counting offers a sensitive, accurate, and rapid approach for determining the activity of ²²³Ra, supporting radiopharmaceutical development and clinical applications.