125Sb to 125mTe branching ratio

The ratio of the 125Sb β-branch to the long-lived isomeric state 125mTe (57.4 days) has been measured by γ-spectrometry to be 0.231±0.010. Since the liquid scintillation counting efficiency is high for both 125Sb (90%) and 125mTe (100%), the determination of this branching ratio by liquid scintillation spectrometry requires one to apply a simultaneous standardization method to radioactive samples in which 125Sb and 125mTe are in full equilibrium.