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Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*
Journal of Environmental Radioactivity, 291, p.107852_1 - 107852_7, 2026/01
Times Cited Count：0 Percentile：0.00(Environmental Sciences)Building materials are the dominant source of indoor thoron. This study preliminarily investigates thoron exhalation rates (JTn) from a gypsum board as part of a cavity wall, comparing them to radon exhalation rates (JRn) from it and to JTn from a solid concrete wall. In situ measurements were conducted over 13 days in an unoccupied ground-floor apartment in Japan using an accumulation chamber and a dedicated thoron and radon monitor. The data showed no significant diurnal variation in JTn, unlike the notable variations observed in JRn. Theoretical calculations indicated that, similar to JRn, JTn was primarily driven by diffusion, with negligible advection due to typical pressure gradients across the gypsum board. Comparison between the gypsum board and solid concrete wall revealed material-specific differences, with noticeable differences observed in the daily averaged JTn and JRn ratios, suggesting that the properties of the gypsum board (or cavity wall) and concrete result affect radon and thoron generation and transport to varying extents, depending on environmental conditions. The calculations also emphasized the importance of key material properties, particularly the radon/thoron diffusion coefficient and thoron concentration difference across the gypsum board. Further research is needed, including long-term monitoring, diverse building materials, and varying environmental conditions. These data are essential for understanding thoron exhalation from cavity walls, improving thoron source characterization, and refining indoor thoron modeling, particularly in environments where thoron contributes significantly to radiation exposure.
Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*
Journal of Environmental Radioactivity, 287, p.107703_1 - 107703_10, 2025/07
Times Cited Count：3 Percentile：58.13(Environmental Sciences)Building materials are one of the most important indoor radon sources, prompting research into their radon exhalation rate (JRn). Most previous studies examining these rates have relied on laboratory tests using pieces or blocks of materials such as concrete and brick. However, creating samples that mimic real cavity walls, defined as walls with a cavity between the two panels of the associated building material, has been challenging owing to structural complexities. In this study, we conducted the first long-term in situ measurement of JRn from the interior board of a common Japanese cavity wall comprising a thin gypsum board (interior wall), air/insulation, and concrete (exterior wall). Results indicated clear diurnal and seasonal variations in the observed JRn data. In general, the highest and lowest JRn values were observed in summer and winter, respectively, exhibiting the same pattern as that observed for thick solid concrete walls analyzed in our previous in situ study. Interestingly, JRn values increased during the day in summer and at night in winter, contrasting with the constant JRn value observed for the thick solid concrete walls over several days. Theoretical calculations indicated that in this case study, JRn was predominantly driven by diffusion, not by advection. These results could be explained by considering the wall thickness, radon diffusivity, and boundary conditions of radon activity concentrations. Our findings can help the selection and refinement of input parameters for radon sources when modeling the spatiotemporal dynamics of indoor radon in buildings. While this study provides new and interesting insights, it is only the first case study, underscoring the need for future in situ tests and the corresponding theoretical analyses across diverse buildings and environments.
Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*
Atmosphere (Internet), 15(6), p.701_1 - 701_12, 2024/06
Times Cited Count：6 Percentile：54.39(Environmental Sciences)Building materials such as brick and concrete are known indoor radon (
Rn) and thoron (
Rn) sources. Most radon and thoron exhalation studies are based on the laboratory testing of pieces and blocks of such materials. To discuss if laboratory findings can be applied to a real-world environment, we conducted intensive in-situ exhalation tests on two solid concrete interior walls of an apartment in Japan for over a year. Exhalation rates of radon (
) and thoron (
) were measured by a measurement system, mainly consisting of an accumulation chamber and dedicated monitors. The indoor air temperature (
) and absolute humidity (
) were measured in parallel, and the wall-surface temperature and water content were occasionally measured. All data obtained here were investigated to reveal environmental and material-associated factors affecting exhalation from the concrete walls. There were weak correlations between or and T or at one tested wall, and moderate correlations of and strong correlations of with or at the other wall. Our findings on were consistent with those in a previous laboratory work where a concrete sample was subject to various temperatures, although a corresponding laboratory study of could not be collected. Additionally, moderate or strong correlation between and was observed for both tested walls. The comparison of the measured data and theoretical calculations revealed a new issue on how much impact each process of the emanation and migration within concrete pore spaces has on radon and thoron exhalation. This study provides an insight into parameterizing radon and thoron source inputs in modeling the spatiotemporal dynamics of indoor radon and thoron.
Hasan, Md. M.*; Janik, M.*; Sakoda, Akihiro; Iimoto, Takeshi*
Environmental Monitoring and Assessment, 193(12), p.770_1 - 770_10, 2021/12
Times Cited Count：2 Percentile：5.13(Environmental Sciences)Potentially higher cancer risk due to exposure from natural background radiation was indicated for Bangladeshi population by estimations based on the countrywide study. Several regions with elevated natural background exhibited higher soil radium and thorium contents than the world average. Being the decay products of these radioactive elements, natural radon isotopes could constitute environmental risk factors for internal radiation exposure to the lungs of people living in these areas. Although lung cancer is one of most prevalent types of cancer in Bangladesh, its status and features are still unclear. To clarify the present status of one of the potential risk factors for lung cancer in the country, this review intends to ascertain the countrywide radon exposure, and its pathways by types of local dwelling and by regions; which would provide an indication of the internal exposures in areas of elevated natural background radiation and radionuclides of soil as well as an understanding of the preliminary contribution of environmental radon on the country's lung cancer prevalence. In this review, countrywide air radon exposures for Bangladeshi dwellings and workplaces are organized from peer-reviewed published papers. Radon has been identified as one of influential sources of radiation dose in Bangladesh with its higher radon exhalation and emanation rate from soil. A novel nationwide depiction of the overall indoor and soil radon levels for Bangladesh has been made through radiation maps. This would be helpful for designing future systematic radon/radiological surveys and research on the country's lung cancer prevalence.
Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Kanzaki, Norie; Iimoto, Takeshi*
no journal, ,
Building materials such as brick and concrete are known to be one of indoor radon (Rn-222) and thoron (Rn-220) sources. Most radon and thoron exhalation studies have been based on laboratory tests using pieces and blocks of such materials. To elucidate how laboratory findings can be used in a real-world environment, we conducted intensive in-situ radon and thoron exhalation tests on interior walls, with different structure types of an apartment (i.e., solid wall and cavity wall) for over a year. This study provides an insight into parameterizing a radon source input in modeling the spatial and temporal dynamics of indoor radon and thoron air concentrations.
Sakoda, Akihiro; Hasan, Md. M.*; Iimoto, Takeshi*
no journal, ,
no abstracts in English
Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*
no journal, ,
no abstracts in English
Sakoda, Akihiro; Hasan, Md. M.*; Kanzaki, Norie; Iimoto, Takeshi*
no journal, ,
Radon is a naturally occurring radioactive gas that can cause lung cancer. Many nationwide and regional surveys, including Japan, on radon concentration in the indoor air of dwellings were implemented in the past couple of decades and compiled by international reports; the annual radon concentration in each nation or region was determined by long-term integrating measurement for dose assessment of the public. On the other hand, efforts of continuous time-resolved monitoring of radon, in addition to relevant environmental factors, have also been made for research purposes to elucidate physical mechanisms of spatial and time variations and elevation of indoor radon concentration as well as to investigate the possibility of predicting annual averages from short- or mid-term measurements. The aims of the present work are to update findings from such measurements and explore what should be future work.
