Implantation of recoiling radionuclides of U and Th radioactive series applied to estimation of surficial erosion of CaCO3 materials

A method to detect the extent of rainfall-dependent erosion of CaCO3 materi als, based on implantation of recoiling nuclei of U-Th disequilibrium serie s (UTHIRN) is outlined here. Radon chambers provided natural implantation o f short and medium-lived isotopes ((212)pb and Pb-210) on surfaces of natur al varieties of CaCO3. Equal thicknesses of CaCO3 were dissolved in order t o measure the distribution of the recoiled nuclei inside the target materia l. The measured distribution was found to be consistent with the theoretica l distribution expected for mechanisms of nuclear stopping. The Po-216 half -recoil range(18 nm) obtained from the experimental curve was slightly high er than the theoretical one (16 nm). The ratio between residual and initial activity, monitored by non-destructive methods, was then used to calculate the eroded thickness of CaCO3 tablets. The 'chemical' and 'mechanical' con tributions of the surficial erosive process were evaluated by leaching expe riments and by simulated rainfall, respectively. Successively, the erosion rates produced during single rainfall events were compared with the experim entally obtained rates, using ternary diagrams (pH/ mm of rainfall/eroded t hickness). The difference between the total eroded thickness measured by th e proposed method (22.5 nm) and the total eroded thickness predicted by the theoretical model (16.9 nm) for the considered rainfalls was about 25%. Th e temporal resolution of the erosion rate, the extension of monitored area and the detail of the surficial eroded thickness (up to similar to 40 nm) a re notably improved by the UTHIRN method. (C) 2001 Elsevier Science Ltd. Al l rights reserved.