DETERMINATION OF RADIOACTIVE BULK AND SURFACE CONCENTRATION BY BETA-DETECTION .3. CORRECTION FOR GAMMA-BACKGROUND

A method for determining bulk or surface activity concentration of bet a-emitters in ''infinitely'' thick or thin samples using energy select ive detectors without any prior chemical separation or qualitative ana lysis was introduced in Part I. In addition to that method, a correcti on procedure is often required in order to compensate for the gamma-se nsitivity of the beta-detector. A system or two - preferably identical - detectors positioned to the front and rear side of a sample has bee n established. The rear side detector is shielded against beta-radiati on. The gamma-response of both detectors is determined as a function o f gamma-energy using monoenergetic calibration standards. Response pul ses are selected to form 8 or 16 energy intervals, and separate series of correction coefficients are then computed for each interval and st andard energy using the ratio of the respective counts. When a sample having mixed beta- and gamma-radiation is evaluated, an ''effective'' gamma-energy is first calculated from the pulse height distribution of the rear side detector, the appropriate series of correction coeffici ents is selected and finally net beta-counts are generated from the co unts of the front side detector. Sensitivities in natural and elevated gamma-background are presented.