Multilabel Counting Using Digital Overlay Technique

The development of electronics has brought multichannel analyzers (MCA's) into liquid scintillation counting. However, the data analysis methods are not on the same level. The currently used window-based calculation methods cannot use all the information measured from the sample. In this presentation a new method called digital overlay technique (DOT) is introduced. This method efficiently uses the information available from the MCA. In DOT, the shape of the Sample spectrum is used for resolving multicomponent samples, by fitting the spectrum of each component to the measured composite spectrum. Furthermore, the fitting of a reference spectrum to the measured spectrum enables the monitoring of sample quality. In this report the basic principles of DOT are illustrated. Measurements made by a liquid scintillation counter, the Wallac 1410, which uses this principle, are presented. Comparisons are made with a conventional window-based method. The results show that DOT gives the best precision irrespective of the activity ratio of the isotopes