A study on the differences in radon exhalation of different lithologies at various depths and the factors influencing its distribution in northern Shaanxi, China

The inhalation of a high concentration of radon gas increases the risk of cancer. Therefore, it is of utmost necessity to pay due attention to the problem of environmental radon pollution. The high radioactivity above the coal slab causes serious radon radiation contamination on the mining grounds in coal mining areas such as the northern part of China and the western part of the United States. At present, there is a lack of research on radon exhalation in different lithologies. In this study, the differences in the radon exhalation of different lithologies at various depths and their controlling factors were studied by NMR and radon measurement. The results highlighted that the radon exhalation rates in different rocks varied from 0.3 to 0.6 Bq/m2·s. The average radon exhalation rate of the soil was 0.7 Bq/m2·s, and the radon exhalation rates of different lithologies followed the pattern red clay > loess > sandstone > mudstone > coal. The radon exhalation rate increased initially, followed by a decrease, and the radon exhalation rate was the highest at the boundary between the soil and rock layers. The radon exhalation rates of different lithologies have a strong correlation with the small pores (<0.1 μm), which govern the changes in the porous structure with depth. The results of this study are important from the perspective evaluation of environmental radon pollution.