Experimental study of the influence of the counter and scintillator on the universal curves in the cross-efficiency method in LSC.

The cross-efficiency method in LSC is one of the approaches proposed for the extension of the Système International de Référence (SIR) to radionuclides emitting no gamma radiation. This method is based on a so-called "universal cross-efficiency curve", establishing a relationship between the detection efficiency of the radionuclide to be measured and the detection efficiency of a suitable tracer. This paper reports a study at LNHB on the influence of the scintillator and of the LS counter on the cross-efficiency curves. This was done by measuring the cross-efficiency curves obtained for (63)Ni and (55)Fe vs. (3)H, using three different commercial LS counters (Guardian 1414, Tricarb 3170 and Quantulus 1220), three different liquid scintillator cocktails (Ultima Gold, Hionic Fluor and PicoFluor 15 from Perkin Elmer(®)), and for chemical and colour-quenched sources. This study shows that these cross-efficiency curves are dependent on the scintillator, on the counter used and on the nature of the quenching phenomenon, and thus cannot definitively be considered as "universal".