DETERMINATION OF RADIOACTIVE BULK AND SURFACE CONCENTRATION BY BETA-DETECTION .1. QUANTITATIVE-ANALYSIS

The activity concentration of bulk and surface samples contaminated wi th 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 distri bution. The counting efficiency of the measuring system changes signif icantly with beta-energy so it cannot be assumed to have a single valu e 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 en ergy intervals. No information is needed on the qualitative compositio n of the sample. Normalised integral distributions (intensity ratios) are derived front the count rates of the intervals. These distribution s are then compared to calibrated intensity ratios obtained with suita ble standard sources. An average (effective) counting efficiency is ge nerated from this comparison by a special algorithm. Activity concentr ation of an unknown sample is then obtained using this average efficie ncy. Calibration and sensitivity data are presented for different type s of bulk and surface samples.