STANDARDIZATION IN LIQUID SCINTILLATION COUNTING

Abstract

This chapter discusses the loss of radioactivity and decreased fluorescence quantum yield regarding how one decides whether a quench correction algorithm is appropriate for a specific sample. For standardization to be valid, the samples must be both homogeneous and similar to the series of standards used to construct quench-correction curves. A homogeneous sample can be defined as one in which the composition of the volume traversed by emitted radiation is the same everywhere. E. B. Muller has proposed a fairly rigorous basic test of homogeneity in surfactant systems: that the efficiency of counting 3 H 2 0 and 3 H-toluene be identical. A somewhat less sensitive but more generally applicable test is the double ratio plot: comparison of a quench correction curve derived using sample channels ratios to one obtained with external standard channels ratios. If the two are discordant for quenched samples the sample is not homogeneous. It is also obvious but probably important to mention that a significant portion of energetic radioactivity may escape altogether from the counting vial. In such a situation, quenching may result in an apparent increase in counting efficiency.