Study of the influence of the liquid scintillator in the Compton efficiency tracing method

The principle of the Compton source efficiency tracing method (CET) in liquid scintillation counting (LSC) is to use, as a tracer, a Compton electron source temporarily created inside the source being measured. The tracer source and the source to measure have thus exactly the same chemical composition. A main advantage anticipated for this measurement method is its low sensitivity to the kB factor and insensitivity to the chemical composition and quenching of the source, which would obviate the necessity to develop a reference liquid scintillator cocktail in the framework of an international reference system for the measurement of pure-beta emitters by LSC. We took the opportunity of a tritiated water international activity measurement in comparison to prepare LS sources using various commercial liquid scintillator cocktails. Tritium is assumed to be a good candidate for testing the LSC activity measurement method, as the detection efficiency is rather low and the effect of the ionization quenching parameter, kB, on the detection efficiency calculation by the TDCR method is known to be important. The sources were measured using a TDCR counter equipped with a Compton spectrometer in order to apply the CET method. The measurements are analyzed using both the TDCR method and CET method in order to deduce the optimal calculation parameters. The detection efficiency range covered by these experiments is from 0.4 to 0.6, allowing a good test of the validity of the physical assumptions included in the calculation model. The paper will conclude on the advantages and drawbacks of using this CET method in the framework of an international reference system for low-energy pure-beta radionuclides.