A simple technique for studying the dependence of radon and thoron exhalation rate from building materials on absolute humidity

Radon exhalation from temperature treated loess

Radon gas is a cancer risk and exists naturally in certain soils, such as loess, which is an important raw earth construction material in arid regions such as northwestern China and southern USA. Accordingly, the radon exhalationed from building materials is of increasing concern; however, there is little research on radon exhalation from loess. In this study, the pore structure and radon exhalation characteristics of heat-treated loess were investigated by nitrogen adsorption tests, swept surface electron microscopy, and radon measurements. The rate of radon exhalation increases linearly with temperature until 400 °C and then decreases exponentially. Changes in the internal pore structure (pore type, surface morphology, and specific surface area) of loess are strongly correlated with the radon exhalation rate. The volume of micropores (<2 nm diameter) is an important influence on radon exhalation ability, which is closely related to the fractal dimension of the micropore structure after heating. The results provide guidance for predicting the radiation risk posed by radon diffusing from loess.

Radiological Characteristics of Carbonated Portland Cement Mortars Made with GGBFS

The objective of this study is to assess whether the carbonation process can modify the physicochemical characteristics of the natural radionuclides of the three natural radioactive series, together with ⁴⁰K. Three mortar specimens with different percentages of ground granulated blast-furnace slag (GGBFS), cured under water for 1, 3, 7, 14, or 28 days, were subjected to a natural carbonation process. Activity concentrations for the solid and ground mortars were determined by gamma spectrometry and by radiochemical separation of isotopic uranium. The novelty of this paper relies principally on the study we have carried out, for the first time, of the radiological characteristics of carbonated Portland cement mortars. It was found that the chemical properties of the 3 mortar specimens were not affected by the carbonation process, with particular attention placed on uranium (²³⁸U, ²³⁵U, and ²³⁴U), the activity concentrations of which were equivalent to the ²²⁶Ra results and ranged from 5.5 ± 1.6 Bq kg⁻¹ to 21.4 ± 1.2 Bq kg⁻¹ for the ²³⁸U. The average activity concentrations for the 3 types of mortars were lower than 20.1 Bq kg⁻¹, 14.5 Bq kg⁻¹, and 120.2 Bq kg⁻¹ for the ²²⁶Ra, ²³²Th (²¹²Pb), and ⁴⁰K, respectively. Annual effective dose rates were equivalent to the natural background of 0.024 mSv. In addition, it was observed that the variation rate for the ²²²Rn emanation was due primarily to the Portland cement hydration and not due to the pore size redistribution as a consequence of the carbonation process. This research will provide new insights into the potential radiological risk from carbonated cement-based materials. Moreover, the assessment that is presented in this study will convey valuable information for future research that will explore the activity concentration of building materials containing NORM materials.

Effect of the pore structure of granite and gabbro after heat treatment on the radon emission rate

The pore structure of rock changes significantly during the heat treatment process, which affects the internal emission rate of radon. This study introduces the results of radon emission rate of rock after high temperature and analyzes the effect of the pore structure in rock mass on radon emission. The results show that there is a good positive correlation between temperature and radon emission in rock mass within a certain temperature range, and the higher the temperature, the higher the radon concentration emission. Two igneous rocks have the rate which is highest after the treatment in 400 °C. The absorption and sealing of radon in the microcapillary are the main occurrences of radon in rock mass. This is reflected in the increase in microcapillary porosity and the decrease in D_P, which changes the microstructure of the rock and increases the connectivity of the internal pore channels of the rock, thereby increasing the volume and length of the migration channels for radon. These results are helpful to understand the influencing mechanism of radon emission process in rocks.

Statistical inferences from measured data on concentrations of naturally occurring radon, thoron, and decay products in Kumaun Himalayan belt

Regional averages of radon, thoron, and associated decay product concentration are reported to be higher than their respective global averages in recent studies conducted in Indian Himalayan belt. The present study explores another region in Indian Himalayan belt by conducting measurements of radon, thoron, and decay product's activity concentration in 92 dwellings of Bageshwar district. The year-long measurements were performed in all 3 seasons distinguishing dwellings as per their construction material. The average radon and thoron concentration for the study region was measured as 57 Bq/m³ and 66 Bq/m³, respectively. Analysis of the measured data in terms of seasonal effects and construction material led to well established inferences, i.e., higher concentration for mud houses and for winter season. In addition, the present study focuses on lesser probed statistical inferences. One of them is related to the appropriateness of frequency distribution function for the measured data and other dwells upon the correlation analysis of inter-related factors for high concentration cases. Three distribution functions (Lognormal, Weibull, and Gamma) were found to be following the trend of frequency distribution curve of the measured data. For mud houses in winter season, variations of radon/thoron concentration were attempted to correlate with mass/surface exhalation rate, emanation rate, and source term content. More than 80% of the dwellings of the study region were found to have gas and decay product's concentration levels, higher than the respective global average values. However, these values were mostly within the reference levels for residential environments. Nevertheless, this region requires further studies to pinpoint the causes for elevated levels and suggest simple remedial modifications if required.