Radioactive Thoron 220Rn Exhalation From Unfired Mud Building Material Into Room Air of Earthen Dwellings

Abstract

Thoron (220Rn), an isotope of radon with a strong α-decay energy, and its short-lived metallic progeny can pose an elevated lung cancer hazard in room air when unfired-soil derived building materials are used in earthen dwellings. Changes in moisture content and density influencing the thoron exhalation rate from earthen materials into room air were studied in the laboratory with terra rossa from a village on the Ðồng Văn Karst Plateau Geopark, Việt Nam, where ethnic minorities construct traditional dwellings with unfired terra rossa walls and floors. Our results show that the thoron exhalation rate from mud surfaces depends on (i) the content of radioactive parental nuclides in mineral components; (ii) the moisture content of mud where ∼5–10 weight % water maximizes the 220Rn exhalation rate; and (iii) the density of dry mud as primarily controlled by internal macroscopic voids, fractures, and porosity. Additional time-series of 220Rn exhalation data from an interior mud wall of a terra rossa-built house under different seasonal and weather conditions show that the temperature is influencing thoron exhalation via the water vapor pressure deficit (VPD) in air and the associated amount of atmospheric moisture adsorbed onto indoor mud surfaces. Our data suggest that occupants of “mud house” earthen dwellings in northern Việt Nam are exposed to an increased thoron geohazard during cooler weather, low VPD, and high relative humidity in air. Detailed studies are needed to evaluate the thoron geohazard for inhabitants of mud-built dwellings in other climates and geological terrains.

Pilot Study of Thoron Concentration in an Underground Thorium Mine

“…The thoron flux from one rock was also investigated by placing it in an air-tight chamber that was connected to the Rad7 as shown in Fig. 2 (Ongori et al, 2016; Nguyen et al 2021). Such exhalation measurements for thoron are quick since the thoron concentration reaches equilibrium within minutes, but the short half-life implies that the measurements are affected by thoron decay in the pipe to the detector; the thoron concentration will not be the same throughout the chamber inside the RAD7, as explained in the RAD7 manual (Durridge 2022).…”

The Determination of Radon/Thoron Exhalation Rate in an Underground Coal Mine—Preliminary Results

“…Therefore, it is difficult to estimate the dose due to 220 Rn and decay products' inhalation, making the estimation of the dose unreliable. Many efforts have been undertaken by numerous groups of scientists to solve these problems [14,[22][23][24][25][26][27][28][29][30]. The estimation of the average 220 Rn concentration in an indoor environment is often based on measurements of thoron exhalation rates, further converted into the average concentration of thoron in the air.…”