Standardization of Tc-99 by three liquid scintillation counting methods

• Activity concentration of Tc-99 solution measured using three LSC methods.
• Methods used are TDCR, CNET and 4π(LS)β–γ coincidence tracing.
• Beta spectral shape confirmed by agreement between three methods.

The NMISA participated in the international key comparison of the pure beta-emitter Technetium-99, CCRI(II)-K2.Tc-99. The comparison solution was standardized using three methods, namely the TDCR efficiency calculation method, the CIEMAT/NIST efficiency tracing method and the 4π(LS)β–γ coincidence tracing method with Co-60 as tracer. Excellent agreement between results obtained with the three methods confirmed the applicability of the beta spectral shape given by the latest (2011) DDEP evaluation of Tc-99 decay data, rather than the earlier (2004) evaluation.