Rapid Estimation of the Concentration of Primordial Radionuclides in Granitic Rocks from Mineral Composition

Abstract

A reliable knowledge of the activity concentrations of the three primordial radionuclides 40K, 238U and 232Th in an environment is crucial to the assessment of both external and internal human exposure to ionizing radiation in the environment. Acquiring activity concentration data on radionuclides in environmental samples can be quite daunting, especially in developing countries, where the cost of gamma spectrometric analysis can be prohibitive. This paper investigated the possibility of estimating activity concentration of granitic rocks from their mineralogical data. A total of 213 granitic rock samples were collected from 71 quarry sites in SW Nigeria for petrographic analysis, using a petrological microscope to view thin sections of the rocks and gamma spectrometric analysis, using a calibrated NaI(Tl) gamma spectrometer to count the samples. Correlation analysis was performed to examine the strength and usability of the correlation between mineral composition and activity concentration in the rocks. Significant relationships were observed between Microcline and 40K (R = 0.92), Biotite and 226Ra (R = 0.86); and Biotite and 232Th (R = 0.87), indicating their good potential for use for the rapid evaluation of natural radionuclides in granitic rock.