[en] Although it is possible to understand each of the basic processes taking place in a liquid scintillation counter, the number of parameters involved, the complex way in which they interact with each other and the difficulty in assessing some of them quantitatively make it virtually impossible to give an accurate mathematical description of the complete liquid scintillation counting process. However, even imperfect mathematical models may eventually become helpful in understanding certain aspects of this process and possibly lead to improvements in measuring methods or instrument design. In recent years, various models have been proposed. The mathematical model presented in this study is a 3-dimensional extension of the model discussed earlier by one of the authors (F.E.L. ten Haaf, in Liquid Scintillation Counting, Vol.2 (eds. M.A.Crook, P.Johnson and B.Scales), Heyden, London 1972,pp.39-48). It is used to generate probability distributions representing pulse height distributions from differently quenched liquid scintillation samples. These are compared with experimentally obtained pulse height distributions. Calculated channels-ratio calibration curves, based on the pulse height distributions produced by the model, are compared with experimentally obtained channels-ratio curves. (author)

[en] Temperature changes affect the calibration of liquid scintillation counting systems, in particular for ³H measurements. By compensating for the temperature coefficient of the gain of the photomultiplier tubes the validity of the calibration can be extended to a wide temperature range. Temperature compensation improves the accuracy of ambient temperature systems. For temperature-controlled counting systems it offers the advantage that calibration curves remain valid, if the temperature of the system is changed. (author)

No abstract available

[en] Computer calculations were made to investigate the relationship between detection efficiency and source position for NaI(Tl) crystals with different well dimensions. It appears that the efficiency in the lower part of the well depends critically on the well depth. This information was used to design a γ well counter with a minimum change in detection efficiency with varying source position. The experimental results show a considerably reduced efficiency change with source position and improved volume independence for liquid samples in comparison with currently used detectors. (author)