“…In such cases, the effect of sample stability on the determination of radionuclide of interest becomes important. The reported researches relevant to sample stability exhibit two problems: (1) Feng et al (2012) have established the usability of expired cocktails, but not the actual constancy of performance characteristics over time, because they have not actually measured long-term changes in the mixture of cocktail and sample; and (2) the quench effect on sample stability had not been mentioned (Verrezen et al, 2008). Quench is the most important issue for LSC (DeVol et al, 2007;Pates et al, 1998;Sosa et al, 2014;Varlam et al, 2015;Zapata-García et al, 2012), which usually leads to reduction in counting efficiency as a result of energy loss in the energy transmission process.…”