Determination of ¹⁶¹Tb half-life by three measurement methods

The radiolanthanide ¹⁶¹Tb is being studied as an alternative to ¹⁷⁷Lu for targeted radionuclide tumor therapy. Both β^--particle emitters show similar chemical behavior and decay characteristics, but ¹⁶¹Tb delivers additional conversion and Auger electron emissions that may enhance the therapeutic efficacy. In this study, the half-life of ¹⁶¹Tb was determined by a combination of three independent measurement systems: reference ionization chamber (CIR, chambre d'ionization de référence), portable ionization chamber (TCIR) and a CeBr₃ γ-emission detector with digital electronics. The half-life determined for ¹⁶¹Tb is 6.953(2) days, showing a significant improvement in the uncertainty, which is one order of magnitude lower, with a deviation of 0.91% from the last nuclear data reference value. The previous large uncertainty of the half-life had a direct impact on activity measurements. Now it is no more an obstacle to a primary standardization.