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Determination of Correlations between Soil Physical Parameters and Radon Exhalation Rates

In this study, we investigated the influence of some soil physical parameters on radon exhalation rates. Soil samples from five different locations, suspected to have different soil textural structures, were analyzed for particle size distribution, ²²⁶Ra concentration, ²²²Rn exhalation rates, hydraulic conductivity, moisture retention, bulk density, and porosity. The ²²⁶Ra activity concentration and ²²²Rn exhalation rates were determined using gamma-ray spectrometry and the closed-can technique, respectively, while the particle size distribution, hydraulic conductivity, moisture retention, bulk density, and porosity were determined using mechanical sieving, constant head, gravimetric, ring test and theoretical calculation methods, respectively. Results of the particle size distribution classified the soil samples into: sandy, sandy loam, loamy sand, and sandy clay loam. The loamy sand sandy clay loam soils presented the highest (0.02050 cm/s) and lowest (0.00043 cm/s) hydraulic conductivity values, respectively. Sandy clay loam had the highest moisture retention (90.40 g), while sandy loam gave the lowest (55.07 g). Sandy clay loam contained the highest ²²⁶Ra activity concentration (237.55±31.37 Bq/kg) while loamy sandy gave the lowest (96.93±29.96 Bq/kg). The average ²²²Rn mass (0.1056 B) and surface (4.4776 Bqm^-2h^-1) exhalation rates from sandy clay loam were higher than all the other soil textures, indicating that areas with sandy clay loam soil may be prone to higher radon exhalations. Generally, the correlation of ²²²Rn mass and surface exhalation rates were strongly positive with ²²⁶Ra concentrations (r = 0.7369), moderately positive with soil moisture retention (r = 0.6020) and porosity (r = 0.4018), but moderately negative with bulk density (r = -0.4018), and weakly negative with hydraulic conductivity (r = -0.2771). The results revealed that ²²⁶Ra concentration and soil moisture retention were the most important factors influencing soil ²²²Rn exhalation rates among the soil textural types examined in this study.

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