Activity standardization of 99mTc using liquid scintillation counting method

The Korea Research Institute of Standards and Science (KRISS) participated in the BIPM.RI(II)-K4.Tc-99 m comparison of activity measurements of ^99mTc. We develop the national primary standard for ^99mTc solution used during the comparison. We use two primary liquid scintillation counting techniques for the standardization: digital coincidence counting with the 4πβ(LS)-γ(NaI(T1))system and triple-to-double coincidence ratio counting. Both methods give consistent results for the specific activity of a ^99mTc solution. Adopting the result from the DCC method as the reference value of the ^99mTc measurement, we evaluate the standard uncertainty of 0.856% for the KRISS primary standard of the ^99mTc activity. The K4 comparison result shows that the newly-established KRISS primary standard lies within the standard uncertainty with the key comparison reference value defined from other ^99mTc measurements.