Effect of Soil Moisture Content on Radon and Thoron Exhalation

Abstract

ÃÃIn this study, the authors considered the effect of soil moisture in the emanation process of radon and thoron gases. Weathered granite soil was selected as the test soil and it was packed in a polypropylene container (275 Â 210 mm 2 and 100 mm in height), up to 50 mm in depth from the bottom. The container was covered with the exhalation rate measuring instrument adopting the accumulation method and -particles were counted at 30 s intervals for 30 min to estimate the exhalation rates. A sporadic increase in the radon and thoron exhalation rates was caused by the increase in the moisture content up to 8%. However, the exhalation rates showed a decreasing tendency with the increase in moisture content over 8%. Although the measured radon exhalation rate was about 25% of the calculated one, both measured and calculated radon exhalation rates had similar trends with an increase in the moisture content in the soil. The measured thoron exhalation rate agreed well with the calculated one. When the moisture content was in the range of 3.5-18%, it was considered that applying the correlation between the moisture content and the measured thoron exhalation rate is useful for estimating the thoron effective diffusion coefficient.

Long-term measurements of residential radon, thoron, and thoron progeny concentrations around the Chhatrapur placer deposit, a high background radiation area in Odisha, India

“…Another reason which can be proposed is dependence of radon (thoron) exhalation from soil/building materials on humidity. In the rainy season, which corresponds to the period during which radon concentration is lowest, the high humidity condition may reduce radon and thoron emanation resulting in a decrease in their exhalation (e.g., Faheem and Matiullah, 2008;Hosoda et al, 2007). In addition, there is a slight difference in radon concentration in the summer and rainy seasons (Table 2).…”

Radon Migration Process and Its Influence Factors; Review

“…The flux density of radon per unit area of the bulk porous medium (radon exhalation rate of pores plus solids), rather than per unit area of the pore air, migrated through soil that results from diffusion can be calculated from Eq.(16). 16,66) …”

“…SCHERY 5) and HOSODA 16) estimated that radon exhalation rate, at dry soil with a very little amount of water content (nearly 0%), increases smoothly with increase water content until it reached 8%. Then the exhalation rate will decrease with increase of water content.…”

Observations and modelling of thoron and its progeny in the soil–atmosphere–plant system

“…1. Although based on nearly 1100 observations, this regression equation eventually could tend to overestimate the diffusion coefficient of radon isotopes at very low (<w5%) soil moisture (Hosoda et al, 2007;Papachristodoulou et al, 2007). This potential uncertainty, however, does not affect the simulations presented here: as our OPUS simulations indicate, volumetric soil moisture even during summer did not drop below 10%.…”