Measurement of the shape-factor functions of the long-lived radionuclides 87Rb, 40K and 10Be

Accurate half-life values for both 87Rb and 40K are essential for geochronological purposes. In another context, the activity determination of the cosmogenic radioisotope 10Be requires a better accuracy, too, so that the records of this radioisotope on the Earth's surface and inside meteorites can be interpreted. Liquid-scintillation counting is an excellent tool for carrying out precise ββ-ray nuclide standardizations. However, the accuracy of the current standardization methods is frequently limited by the presence of inaccuracies in the shape-factor function. In this work, the shape-factor functions of 87Rb, 40K and 10Be are determined by experiment and compared with theoretical predictions. The measured shape-factor functions of 87Rb and 10Be were in good agreement with theory, but for 40K, some unexpected deviations were detected which make further investigations necessary.