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

Abstract

A method to detect the extent of rainfall-dependent erosion of CaCO3 materials, based on implantation of recoiling nuclei of U–Th disequilibrium series (UTHIRN) is outlined here. Radon chambers provided natural implantation of short and medium-lived isotopes (212Pb and 210Pb) on surfaces of natural varieties of CaCO3. Equal thicknesses of CaCO3 were dissolved in order to measure the distribution of the recoiled nuclei inside the target material. The measured distribution was found to be consistent with the theoretical distribution expected for mechanisms of nuclear stopping. The 216Po half-recoil range (18 nm) obtained from the experimental curve was slightly higher 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’ contributions of the surficial erosive process were evaluated by leaching experiments and by simulated rainfall, respectively. Successively, the erosion rates produced during single rainfall events were compared with the experimentally obtained rates, using ternary diagrams (pH/ mm of rainfall/eroded thickness). The difference between the total eroded thickness measured by the 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%. The temporal resolution of the erosion rate, the extension of monitored area and the detail of the surficial eroded thickness (up to ∼40 nm) are notably improved by the UTHIRN method.