Desktop calculator-assisted liquid scintillation spectrometry of 3H and 14C with special consideration of low level activities and spectrometer instability. Chapter 17

For the liquid scintillation measurement of 3H and 14C in single- and dual-labelled samples with the same spectrometer settings, which are desirable for routine work, the lower discriminator level of the 14C channel has to be set down to a value for which the tritium crosstalk α amounts to about 15%. Under these conditions, the short time variations of α are important for the overall attainable precision. A simple method for the automatic computation of drift corrections based on the continuous measurement of a standard sample is presented. Furthermore, for low activities an appreciable improvement of the precision may be achieved by systematic re-use of the glass vials together with the cumulated measurements of their individual backgrounds. The precision of low activity measurements is also enhanced by correction of background counting rates for quenching. (author)