A DETAILED STUDY OF THE RELIABILITY OF SOME CRUCIAL PARAMETERS USED IN THE IN-SITU RADIOTRACER SORPTION STUDIES

In the present work we report an upgraded version of the radiotracer ' thin gap' ('electrode lowering') method and give a brief overview on t he contribution of the secondary radiations (bremsstrahlung, character istic X-rays, and backscattered beta-particles) to the beta-intensitie s to be detected during in-situ radiotracer sorption experiments. The results, measured by various scintillation detectors (plastic and Li-g lass with thicknesses of 0.1 to 5 mm) using pure beta-emitting radiois otopes of E-beta max (maximum beta-energy) of 67-1710 keV, reveal that (i) at E-beta max greater than or equal to 155 keV the contribution o f the induced X-rays to the gross counting rate, irrespective of the t ype and thickness of the scintillation materials, is very small (less than 3.5%); (ii) at E-beta max less than or equal to 67 keV (e.g. H-3, Ni-63) the relative amounts of bremsstrahlung seem to be high (exceed ing 15%), (iii) the intensity of backscattered beta-particles is appar ently dependent upon not only the average atomic number of the scatter er (adsorbent), but E-beta max of the incident beta-radiation. In orde r to demonstrate the reliability and versatility of a version of the ' thin gap' technique illustrative examples for the in-situ radiotracer studies of various sorption phenomena (such as adsorption of bisulfate /sulfate on gold, accumulation of 1-hydroxyethane-1,1-diphosphonic aci d (HEDP) on iron, and deposition of silver on austenitic stainless ste el) are also presented and discussed. Most of the implications summari zed in this paper are valid for the in-situ radiotracer 'foil' method, too. (C) 1998 Elsevier Science S.A. All rights reserved.