Radon soil–gas as a geological mapping tool case

Authors: A A Adepelumi T R Ajayi B D Ako A O Ojo

Publish Date: 2005/07/19

Volume: 48, Issue: 6, Pages: 762-770

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Abstract

In an effort to quantify the geogenic radon soil–gas potential and appraise the use of radon technique as a geological mapping tool in a crystalline basement rock terrain of Ile–Ife Nigeria radon measurement concentration were made using a radon detector instrument EDA RD200 that measures radon isotopes by a scintillator cell coupled to a photomultiplier tube The data were collected from soils derived from three different lithologic rock units The observed values were then correlated with the geology of the area Significant differences in the radon soil–gas concentrations among the three geologic units were observed Granite gneiss has the highest concentration followed by grey gneiss and mica schist in that order The geometric mean GM concentration of radon222 measured in soils directly overlying the three different rock types were 3014 pCi/l for granite gneiss 2028 pCi/l for the grey gneiss and 1994 pCi/l for mica schist Conversely the average values for radon220 averaged 15100 8154 and 7330 pCi/l for granite gneiss grey gneiss and mica schist rocks respectively Statistical t test α=005 results indicated that there was no significant difference in the geometric mean of radon soil–gas measured between low and medium potential zones However significant differences were found between the low and high radon potential zones and between the medium and high zones The low concentrations of radon soil–gas emission observed in this study is explained in terms of the seasonal variation due to thermal convection fluid movement while the radon concentrations were found to be controlled by the lithology and geochemistry of the underlying bedrockThe first author is grateful to the South Korean government for granting him a postdoctoral fellowship that enabled him to carry out the research at the Korea Institute of Geoscience and Mineral Resources Daejeon South Korea The counting equipment used for this work was a donation from the IAEA Austria The authors are deeply grateful for these supports

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