Determination of radioactive bulk and surface concentration by beta-detection .1. Quantitative analysis

The activity concentration of bulk and surface samples contaminated with beta-emitting radioisotopes is difficult to measure without the ''a priori'' knowledge of the nature of the non-gamma emitting components. Beta-emitters cannot be identified from any measured spectral distribution. The counting efficiency of the measuring system changes significantly with beta-energy so it cannot be assumed to have a single value obtained with a standard source with known energy. Application of an energy selective beta-detector is introduced for determining bulk and surface activity concentration. Samples of ''infinitely thick'' or ''infinitely thin'' nature are to be prepared. The distribution of beta-energy deposited in the detector is registered as counts in 8 or 16 energy intervals. No information is needed on the qualitative composition of the sample. Normalised integral distributions (intensity ratios) are derived front the count rates of the intervals. These distributions are then compared to calibrated intensity ratios obtained with suitable standard sources. An average (effective) counting efficiency is generated from this comparison by a special algorithm. Activity concentration of an unknown sample is then obtained using this average efficiency. Calibration and sensitivity data are presented for different types of bulk and surface samples.