A simple counting technique for measuring mixtures of two pure β-emitting radionuclides

A simple counting technique to measure mixtures of two pure β-emitting radionuclides is described. The method is based on elements of two liquid scintillation techniques that are widely used to measure single-radionuclide solutions, namely the triple-to-double coincidence ratio (TDCR) efficiency calculation technique and the CIEMAT/NIST efficiency tracing method. Double- and triple-coincidence count rates, together with the figure-of-merit P determined from an external tracer, are used to extract the component activities of a source. A simulation was used to gauge the effect of counting statistics on the method's ability to extract a mixture composition under normal counting conditions and to validate derived uncertainty formulas based on counting statistics. The method is demonstrated experimentally for various mixture combinations of 14C and 63Ni. It is shown that the accuracy of the technique can be enhanced by improving the determination of the figure-of-merit.