Introduction

The triple-to-double coincidence ratio (TDCR) method is a technique in liquid scintillation counting (LSC) specifically designed for determining the massic activity of pure β- and pure electron capture (EC) emitters in solution. Considered an absolute technique, it relies on decay scheme data to calculate detection efficiency. In 2013, LBIOVT introduced a novel approach for assessing 210Pb levels via LSC. In this study, we evaluate and compare this approach against TDCR values across various regions of interest (ROIs). In this complementary work, the efficiency was evaluated and compared to the TDCR value for different regions of interest (ROIs).

Methodology

Following the established radiochemical procedure from prior research, three water samples in nitric acid were spiked with known activities of ²¹⁰Pb standard solution provided by the National Laboratory of Ionizing Radiations Metrology (LNMRI). Additionally, one non-spiked sample was processed as a blank. Subsequently, all four samples underwent the radiological procedure. The samples were prepared in plastic scintillation vials, each containing 20 mL of Hisafe 3, with the filtered precipitation settled at the bottom of the vial. Analysis was conducted using a TDCR Hidex 300 SL instrument equipped with an a/b discriminator and MikroWin software for parameter control and spectrum analysis. Counting parameters were set for alpha activity type, with a preset PLI limit of 65 and a counting time of 3600 seconds. Counting was performed daily post-precipitation, followed by calculations to compare efficiency with the TDCR value.

Results

A spectrum corresponding to the ²¹⁰Pb+²¹⁰Bi one day after precipitation and after achieving secular equilibrium was analyzed. Specific ROIs were defined: 0-350 for 210Pb counts, 351-1023 for 210Bi contributions, and 0-1023 for total contributions (210Pb + 210Bi). Initial findings suggest agreement between TDCR and efficiency values for ROI [0-350], from day one to equilibrium, reflecting consistency in the behavior of 210Pb as a pure beta emitter. Ongoing investigation into efficiency and TDCR values for ROI [351-1023] (210Bi) and ROI [0-1023] (total contributions) will be detailed in subsequent updates.

Conclusion

This work is currently ongoing and is anticipated to yield consistent results for the TDCR and efficiency values when considering the ROI corresponding to the behavior of the radionuclide as a pure beta emitter. Further exploration into TDCR behavior concerning non-pure beta emitters remains underway.