2022 Fiscal Year Research-status Report
Spatial distribution of radon and thoron in the soil around active faults as a contribution to the elevated indoor radon
| Project/Area Number |
21K12228
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| Research Institution | National Institutes for Quantum Science and Technology |
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Principal Investigator |
Janik Miroslaw 国立研究開発法人量子科学技術研究開発機構, 放射線医学研究所 計測・線量評価部, 研究員 (30833933)
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| Co-Investigator(Kenkyū-buntansha) |
小平 聡 国立研究開発法人量子科学技術研究開発機構, 放射線医学研究所 計測・線量評価部, グループリーダー (00434324)
ゴメス クリストファー 神戸大学, 海事科学研究科, 教授 (20800577)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | radon / thoron / active fault / permeability / carbon dioxide |
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| Outline of Annual Research Achievements |
We analysed the data from the first measurements taken near the Fugendake volcano (U1). The radon concentration was lower than expected with low variation of horizonal nor vertical distribution. We therefore chose another active fault site, with a different geological structure near Takayama city (T1). Radon (Rn) and thoron (Tn) concentrations in soil gas with an active device together with radon exhalation rate, soil permeability and CO2 were measured. Measurements of Ra and Th in the collected soil samples were carried out using HPGe detector. Bulk density and porosity of soil samples were determined. Geophysical methods combined with the standard geotechnical cone penetrometer were used to recognize the geological structure and soil characteristics of the area and locate the predicted faults positions and routes. Obtained data were prepared as an input for the radon diffusion-convection transport model.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The scope of activities set for this year has been fulfilled. As a result of measurement, at point T1 a significant increase in the concentration of radon and thoron was observed in the vicinity of the geological fault. In contrast, at the second point (U1), changes in the radon and thoron concentration near the fault were small. At site T1, radon concentrations range from 5 to 75 kBq/m3, with the highest value occurring on the fault, and thoron from 11 to 37 kBq/m3. At the U1 site radon concentration ranged from 4-5.5 kBq/m3, and thoron from 13 to 23 kBq/m3. At both sites we found a moderate/strong correlation between radon and CO2 concentrations whereas the correlation between permeability and radon is weak.
We can assume that such a large discrepancy between measured radon value cannot be explained by the soil formation alone, and one possible explanation is the difference between the types of faults.
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| Strategy for Future Research Activity |
A third measurement campaign is in the pipeline for the final year of the project. The collected data will be used to improve the results of the model. The model output will be both the vertical distribution of radon in soil and the simulation of radon entry rate into a typical (hypothetical) house. The algorithms for evaluating the location of faults will also be improved. The results of the project will be presented at international workshops and conferences and will be published in international scientific journals.
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| Causes of Carryover |
Travel expenses have been reduced due to COVID-19 travel restrictions. Participation in the international conference in connection with on-site experiment is planned. Maintenance and calibration of device will be carried out.
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