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Journal Articles

Evaluation of indoor radon risk for discussion on national action in Japan

Sakoda, Akihiro; Ishimori, Yuu

Hoken Butsuri (Internet), 59(3), p.109 - 117, 2024/09

International organizations such as WHO and ICRP recommended reference levels with the range of 100$$sim$$300 Bq/m$$^{3}$$ against residential radon exposure. In Japan, indoor radon activity concentration is generally low, and a national plan and reference level have not been set so far. This study aimed to evaluate the risks of indoor radon among Japanese populations and to discuss the effectiveness of an assumed reference level in terms of reduction in the number of lung cancer deaths. The US EPA model was used to calculate lifetime risks and population attributable fractions for ever smokers and never smokers using the recent Japanese-specific information such as demographic data and smoking prevalence. The result indicated that the number of lung cancer deaths was very low (i.e., less than 10 in 2020) among the population exposed to more than 100 Bq/m$$^{3}$$. This means that even if a reference level of 100 Bq/m$$^{3}$$ is set, the statistically significant reduction in lung cancer deaths could not be observed. Given the risk evaluation, we believe that expected national actions in Japan are to support individuals who consider taking measures for the own risk perception and control of lifetime risk, rather than to introduce regulations. Comprehensive argument and judgement would also be desired for better public health, based on information on not only radon but also other common modifiable risk factors.

Journal Articles

Beryllium-7 depositions in Hokuriku, Japan in winter (1991-2021); Factors causing the temporal variation

Yoshida, Keisuke; Kato, Shingo; Okuyama, Shinichi; Ishimori, Yuu; Inoue, Mutsuo*

Journal of Nuclear and Radiochemical Sciences (Internet), 24, p.1 - 12, 2024/08

Journal Articles

Seasonal variations in radon and thoron exhalation rates from solid concrete interior walls observed using in situ measurements

Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*

Atmosphere (Internet), 15(6), p.701_1 - 701_12, 2024/06

Building materials such as brick and concrete are known indoor radon ($$^{222}$$Rn) and thoron ($$^{220}$$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 ($$J_{rm Rn}$$) and thoron ($$J_{rm Tn}$$) were measured by a measurement system, mainly consisting of an accumulation chamber and dedicated monitors. The indoor air temperature ($$T$$) and absolute humidity ($$AH_{rm in}$$) 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 $$J_{rm Rn}$$ or $$J_{rm Tn}$$ and T or $$AH_{rm in}$$ at one tested wall, and moderate correlations of $$J_{rm Rn}$$ and strong correlations of $$J_{rm Tn}$$ with $$T$$ or $$AH_{rm in}$$ at the other wall. Our findings on $$J_{rm Rn}$$ were consistent with those in a previous laboratory work where a concrete sample was subject to various temperatures, although a corresponding laboratory study of $$J_{rm Tn}$$ could not be collected. Additionally, moderate or strong correlation between $$J_{rm Rn}$$ and $$J_{rm Tn}$$ 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.

Journal Articles

Improved data analysis techniques for calculating more accurate radon and thoron exhalation rates from building interior solid walls

Sakoda, Akihiro; Ishimori, Yuu; Jin, Q.*; Iimoto, Takeshi*

Applied Radiation and Isotopes, 207, p.111180_1 - 111180_8, 2024/05

 Times Cited Count:0 Percentile:0.05

The impacts of mathematical models and associated parameters on radon ($$^{222}$$Rn) and thoron ($$^{220}$$Rn) exhalation rates based on in-situ testing at building interior solid walls were demonstrated to improve data analysis techniques. The results showed that the heterogeneity of their activity concentrations within the measurement system was more significant for thoron than radon. The diurnal variation in indoor radon should be considered for better data quality. In conclusion, a model should be appropriately made and selected under the purposes and accuracy requirements of the exhalation test.

Journal Articles

Environmental monitoring of trace elements and evaluation of environmental impacts to organisms near a former uranium mining site in Nigyo-toge, Japan

Horai, Sawako*; Murakami, Shoichi*; Sakoda, Akihiro; Nakashita, Rumiko*; Kunisue, Tatsuya*; Ishimori, Yuu

Environmental Monitoring and Assessment, 194(6), p.415_1 - 415_25, 2022/06

 Times Cited Count:3 Percentile:38.08(Environmental Sciences)

This study conducted an investigation of trace element behavior at a former uranium (U) mining site and evaluated environmental impacts to biota. Concentrations of trace elements were determined in sediments, water, and three organism types (insects, frogs, and newts) from three zones in the former U mining site. Concentrations of As and U in the sediments and water samples were the highest at the mill tailings pond site, where post-U extraction remnants have been accumulated. Additionally, among the organisms analyzed the highest levels of these elements/isotopes were found in newts from MP. Considering data analyses of the whole-body element concentrations, bioaccumulation factors, and $$delta$$$$^{15}$$N values for the organisms, it was concluded that newts might be the most vulnerable species in this location. Further monitoring and more accurate evaluation of the ecological impacts are preferred for this former U mining site.

Journal Articles

Dosimetry of radon progeny deposited on skin in air and thermal water

Sakoda, Akihiro; Ishimori, Yuu; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*

Journal of Radiation Research (Internet), 62(4), p.634 - 644, 2021/07

 Times Cited Count:3 Percentile:35.49(Biology)

It is held that the skin dose from radon progeny is not negligibly small and that introducing cancer is a possible consequence under normal circumstances, while there are a number of uncertainties in terms of related parameters such as activity concentrations in air, target cells in skin, skin covering materials, and deposition velocities. Meanwhile, an interesting proposal emerged in that skin exposure to natural radon-rich thermal water as part of balneotherapy can produce an immune response to induce beneficial health effects. The goal of the present study was to obtain generic dose coefficients with a focus on the radon progeny deposited on the skin in air or water in relation to risk or therapeutic assessments. We thus first estimated the skin deposition velocities of radon progeny in the two media based on data from the latest human studies. Using the optimized velocities, skin dosimetry was then performed under different assumptions regarding alpha-emitting source position and target cell (i.e., basal cells or Langerhans cells). Furthermore, the impact of the radon progeny deposition on effective doses from all exposure pathways relating to "radon exposure" was assessed using various possible scenarios. It was found that in both exposure media, effective doses from radon progeny inhalation are one to four orders of magnitude higher than those from the other pathways. In addition, absorbed doses on the skin can be the highest among all pathways when the radon activity concentrations in water are two or more orders of magnitude higher than those in air.

Journal Articles

Methodology for simple spot measurement of equilibrium equivalent radon concentration

Sakoda, Akihiro; Ishimori, Yuu; Kanzaki, Norie; Tanaka, Hiroshi

Radiation Protection Dosimetry, 191(4), p.383 - 390, 2020/10

 Times Cited Count:1 Percentile:11.54(Environmental Sciences)

Estimation of the effective inhalation dose of short half-life radon progeny requires the quantification of radon equilibrium equivalent activity concentrations (EEC). The aim of the present study is to develop new methodology that focuses on spot measurements to determine EEC from single gross alpha counts and determine an optimized protocol. The core of the approach is to measure alpha particles over time when the radon progeny attached to the sampling filter are significantly disintegrated. The calibration curve of single counts to EEC is theoretically deduced and validated by a comparison test. The advantage of the present method is its minimal requirements, including the use of common instruments and simple sampling, alpha counting, and analysis procedures. This approach offers an option for radon practitioners working in a variety of fields, as well as the possibility for non-experts to easily measure EEC.

Journal Articles

Comparison of antioxidative effects between radon and thoron inhalation in mouse organs

Kobashi, Yusuke*; Kataoka, Takahiro*; Kanzaki, Norie; Ishida, Tsuyoshi*; Sakoda, Akihiro; Tanaka, Hiroshi; Ishimori, Yuu; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*

Radiation and Environmental Biophysics, 59(3), p.473 - 482, 2020/08

 Times Cited Count:5 Percentile:38.99(Biology)

Radon therapy has been traditionally performed globally for oxidative stress-related diseases. Many researchers have studied the beneficial effects of radon exposure in living organisms. However, the effects of thoron, a radioisotope of radon, have not been fully examined. In this study, we aimed to compare the biological effects of radon and thoron inhalation on mouse organs with a focus on oxidative stress. Male BALB/c mice were randomly divided into 15 groups: sham inhalation, radon inhalation at a dose of 500 Bq/m$$^{3}$$ or 2000 Bq/m$$^{3}$$, and thoron inhalation at a dose of 500 Bq/m$$^{3}$$ or 2000 Bq/m$$^{3}$$ were carried out. Immediately after inhalation, mouse tissues were excised for biochemical assays. The results showed a significant increase in superoxide dismutase and total glutathione, and a significant decrease in lipid peroxide following thoron inhalation under several conditions. Additionally, similar effects were observed for different doses and inhalation times between radon and thoron. Our results suggest that thoron inhalation also exerts antioxidative effects against oxidative stress in organs. However, the inhalation conditions should be carefully analyzed because of the differences in physical characteristics between radon and thoron.

Journal Articles

Concentration ratios of $$^{238}$$U and $$^{226}$$Ra for insects and amphibians living in the vicinity of the closed uranium mine at Ningyo-toge, Japan

Sakoda, Akihiro; Murakami, Shoichi*; Ishimori, Yuu; Horai, Sawako*

Journal of Radiation Research (Internet), 61(2), p.207 - 213, 2020/03

 Times Cited Count:1 Percentile:10.27(Biology)

JAEA Reports

Research of the tasks on risk communication enforcement in fiscal year 2016 (Contract research)

Tanaka, Masaru*; Kawara, Osami*; Ishizaka, Kaoru*; Ohata, Yuki*; Fukuike, Iori*; Kawase, Keiichi; Tokizawa, Takayuki; Miyagawa, Hiroshi*; Ishimori, Yuu

JAEA-Research 2018-001, 98 Pages, 2018/06

JAEA-Research-2018-001.pdf:2.49MB

In the 2016 fiscal year, communication cases on general waste disposal facility construction plans in recent years were surveyed. Results suggested as follows: (1) Existing long-term relationships or agreements in local area promote local accepting. (2) An operator needs to consider alternative plans and explain reasons for the decision making to local stakeholders. (3) Even after first announcement of a new plan, an operator needs to review the plan depending on local concerns. (4) Announcement of a new plan will activate communications on local development including the site redevelopment.

Journal Articles

Production and detection of fission-induced neutrons following fast neutron direct interrogation to various dry materials containing $$^{235}$$U

Sakoda, Akihiro; Nakatsuka, Yoshiaki; Ishimori, Yuu; Nakashima, Shinichi; Komeda, Masao; Ozu, Akira; Toh, Yosuke

Journal of Nuclear Science and Technology, 55(6), p.605 - 613, 2018/06

 Times Cited Count:1 Percentile:11.24(Nuclear Science & Technology)

For better nuclear material accountancy, we had developed a non-destructive assay system dedicated to uranium waste drums (JAWAS-N: JAEA Waste Assay System at Ningyo-toge). The system is based on a fast neutron direct interrogation (FNDI) method. To clarify the characteristics of the FNDI method and the performance of JAWAS-N, experimental and computational mock-up tests were carried out using various dry materials that contained known amounts of natural uranium. As a result, linearity between the die-away time ($$tau$$$$_{2}$$) and the counts of fast neutrons attributed to $$^{235}$$U fission was confirmed experimentally and analytically. Moreover, the MCNP simulation was performed to discuss the radial and axial dependences of $$^{235}$$U fission probability, neutron detection efficiency, and sensitivity on uranium distributions in the drum. The simulation results agreed with the empirical results reported in a previous paper, providing valuable information on the practice of FNDI-based uranium determination. Furthermore, the nominal detection limits of natural uranium in JAWAS-N were estimated to be 15, 4, and 2 g for $$tau$$$$_{2}$$ = 0.2, 0.3, and 0.4 msec, respectively. The findings obtained here will contribute to the implementation of the FNDI method to assess the quantities of $$^{235}$$U in actual uranium waste drums.

Journal Articles

Comparative effects of radon inhalation according to mouse strain and cisplatin dose in a cisplatin-induced renal damage model

Sasaoka, Kaori*; Kataoka, Takahiro*; Kanzaki, Norie; Kobashi, Yusuke*; Sakoda, Akihiro; Ishimori, Yuu; Yamaoka, Kiyonori*

Pakistan Journal of Zoology, 50(3), p.1157 - 1170, 2018/06

 Times Cited Count:2 Percentile:17.03(Zoology)

Cisplatin (CDDP) is widely used for treating solid cancers; however, it induces nephrotoxicity caused by oxidative stress. Here, we investigated whether radon inhalation has different effects against CDDP induced renal injury in two mouse strains differing in radiosensitivity, and determined the appropriate dose of CDDP combined with radon inhalation for highly radiosensitive mice. CDDP was administered at 20 mg/kg weight to C57BL/6J and BALB/c mice after radon inhalation at 1000 Bq/m$$^{3}$$ and 2000 Bq/m$$^{3}$$ for 24 h. Radon inhalation had a slight positive effect against CDDP toxicity in C57BL/6J mice with respect to improved hair condition, whereas radon inhalation exacerbated CDDP-induced toxicity in BALB/c mice. When BALB/c mice were treated with a lower dose of CDDP (15 mg/kg) after 1000 Bq/m$$^{3}$$ radon inhalation, the creatinine level was reduced and the superoxide dismutase content was increased. The supportive effect of radon inhalation shows its good potential as a candidate treatment to alleviate CDDP-induced renal damage.

JAEA Reports

The Annual report on the environmental monitoring around the waste rock sites 2016 Tottori

Ono, Takayuki; Kawasaki, Satoru; Ishimori, Yuu; Ando, Masaki

JAEA-Review 2017-044, 13 Pages, 2018/03

JAEA-Review-2017-044.pdf:1.17MB

The Ningyo-toge Environmental Engineering Center of the Japan Atomic Energy Agency performs the environmental monitoring around the Ningyo-toge and the waste rock sites according to the agreements with local governments, Okayama and Tottori prefectures. Each prefectural committee on the environmental monitoring evaluates the monitoring data annually. This report summarized the results of the environmental monitoring in Tottori prefecture in the fiscal year 2016. The results show that the levels of the radiation doses and the radioactive concentrations in the environment were within natural variations, and the waste rock sites have been well maintained. The committee concluded that the environmental impacts from the sites were negligible.

JAEA Reports

The Annual report on the environmental monitoring around the Ningyo-toge 2016; Okayama

Ono, Takayuki; Kawasaki, Satoru; Ishimori, Yuu; Ando, Masaki

JAEA-Review 2017-043, 39 Pages, 2018/03

JAEA-Review-2017-043.pdf:1.92MB

The Ningyo-toge Environmental Engineering Center of the Japan Atomic Energy Agency (JAEA Ningyo-toge) performs the environmental monitoring around the Ningyo-toge and the waste rock sites according to the agreements with local governments, Okayama and Tottori prefectures. Environmental monitoring of plutonium has been also performed around the Ningyo-toge regarding the practical application study on the reprocessed uranium conversion, which was carried out from 1994 to 1999 at the Ningyo-toge. Each prefectural committee on the environmental monitoring evaluates the monitoring data annually. This report summarized the results of the environmental monitoring in Okayama prefecture in the fiscal year 2016. The results show that the levels of the radiation doses and the radioactive concentrations in the environment were within natural variations, and the committee concluded that the environmental impacts from the sites were negligible. Therefore, the site of the JAEA Ningyo-toge has been well operated, and the waste rock sites have been well maintained.

Journal Articles

Knowledge discovery of suppressive effect of disease and increased anti-oxidative function by low-dose radiation using self-organizing map

Kanzaki, Norie; Kataoka, Takahiro*; Kobashi, Yusuke*; Yunoki, Yuto*; Ishida, Tsuyoshi*; Sakoda, Akihiro; Ishimori, Yuu; Yamaoka, Kiyonori*

Radioisotopes, 67(2), p.43 - 57, 2018/02

We previously reported that low-dose radiation induces the anti-oxidative function in many organ systems of mice. This results in the suppression of several kinds of oxidative stress-induced damage. This study was conducted with the objective of revealing the health effects of low-dose radiation obtained from our previous reports and searching for a new treatment based on low-dose radiation, such as radon therapy. We extracted the characteristics of the effects of low dose radiation suppressing diseases and enhancing the anti-oxidative function using fuzzy answer by self-organizing map (SOM) based on mutual knowledge. The relationship between the suppressive effect and increased antioxidative function was shown in our result, and the concentration dependence of the effect against pain was shown on the output map. Although the effect against other organs depending on concentration was unpredictable, our results indicate that low-dose radiation may also be suitable for treatment of liver disease and brain disease.

Journal Articles

Mechanisms and modeling approaches of radon emanation for natural materials

Sakoda, Akihiro; Ishimori, Yuu

Hoken Butsuri, 52(4), p.296 - 306, 2017/12

Radon emanation means the escape of radon atoms from solid grains into pore space; it is the very first process that may lead to radon exposure in the environment. Experimental and numerical studies of radon emanation have been diligently carried out since its recognition as a carcinogen. Our previous review of the measured data showed a wide range of radon emanation fractions from natural substances, and then we discussed the effects of environmental factors such as pore water. The present paper provides an overview of the approaches and progress of radon emanation modeling that may be useful for the interpretation of measured data. Recoil and/or diffusion of radon in solid following alpha decay of radium, which underlies the mechanisms of radon emanation, have been incorporated into numerical models. In the calculation based on recoil-based emanation, radium distribution and pore size were the most important parameters, which govern the magnitudes of radon ejections from the birth grain and of radon embedding into another solid surface, respectively. The solid diffusion appeared significant only at a temperature higher than a few hundred degrees Celsius. A model is now desired to be developed that incorporates the transport process of radon atoms that are still settled in solid after alpha recoil, considering radiation damage and its resulting inner path network.

JAEA Reports

Research of the tasks on risk communication enforcement in fiscal year 2015 (Contract research)

Tanaka, Masaru*; Aoyama, Isao*; Ishizaka, Kaoru*; Ohata, Yuki*; Fukuike, Iori*; Kawase, Keiichi; Watanabe, Masanori; Tokizawa, Takayuki; Miyagawa, Hiroshi*; Ishimori, Yuu

JAEA-Research 2017-003, 65 Pages, 2017/06

JAEA-Research-2017-003.pdf:2.92MB

JAEA Ningyo-toge Environmental Engineering Center and Fukushima Environmental Safety Center have same challenges in risk communication. As reference, similar domestic cases were investigated by our two Centers, and requirements for building long-term relationship were clarified. As follows; (1) Develop new relationship with various stakeholders in the region. (2) Make better use of existing resources (personnel, land and facilities, etc.). (3) Make a concerted effort to create new values with local stakeholders. (4) Make an opportunity which local stakeholders confirm safety and build confidence to the project. These efforts will enhance the opportunities for operators and residents to learn about environment management and environmental protection.

Journal Articles

Protective effects of hot spring water drinking and radon inhalation on ethanol-induced gastric mucosal injury in mice

Etani, Reo*; Kataoka, Takahiro*; Kanzaki, Norie*; Sakoda, Akihiro; Tanaka, Hiroshi; Ishimori, Yuu; Mitsunobu, Fumihiro*; Taguchi, Takehito*; Yamaoka, Kiyonori*

Journal of Radiation Research, 58(5), p.614 - 625, 2017/05

 Times Cited Count:13 Percentile:56.15(Biology)

Radon therapy using radon ($$^{222}$$Rn) gas is classified into two types of treatment: inhalation of radon gas and drinking water containing radon. Although short- or long-term intake of spa water is effective in increasing gastric mucosal blood flow, and spa water therapy is useful for treating chronic gastritis and gastric ulcer, the underlying mechanisms for and precise effects of radon protection against mucosal injury are unclear. In the present study, we examined the protective effects of hot spring water drinking and radon inhalation on ethanol-induced gastric mucosal injury in mice. Mice inhaled radon at a concentration of 2000 Be/m$$^{3}$$ for 24 h or were provided with hot spring water for 2 weeks. The activity density of $$^{222}$$Rn ranged from 663 Bq/l (start point of supplying) to 100 Bq/l (end point of supplying).Mice were then orally administered ethanol at three concentrations. The ulcer index (UI), an indicator of mucosal injury, increased in response to the administration of ethanol; however, treatment with either radon inhalation or hot spring water inhibited the elevation in the UI due to ethanol. Although no significant differences in antioxidative enzymes were observed between the radon-treated groups and the non-treated control groups, lipid peroxide levels were significantly lower in the stomachs of mice pre-treated with radon or hot spring water. These results suggest that hot spring water drinking and radon inhalation inhibit ethanol-induced gastric mucosal injury.

Journal Articles

Measurements of radon activity concentration in mouse tissues and organs

Ishimori, Yuu; Tanaka, Hiroshi; Sakoda, Akihiro; Kataoka, Takahiro*; Yamaoka, Kiyonori*; Mitsunobu, Fumihiro*

Radiation and Environmental Biophysics, 56(2), p.161 - 165, 2017/05

 Times Cited Count:8 Percentile:40.98(Biology)

In order to investigate the biokinetics of inhaled radon, radon concentrations in mouse tissues and organs were determined after mice had been exposed to about 1 MBq/m$$^{3}$$ of radon in air. Radon concentrations in mouse blood and in other tissues and organs were measured with a liquid scintillation counter and with a well-type HP Ge detector, respectively. Radon concentration in mouse blood was 0.410$$pm$$0.016 Bq/g when saturated with 1 MBq/m$$^{3}$$ of radon concentration in air. In addition, average partition coefficients obtained were 0.74$$pm$$0.19 for liver, 0.46$$pm$$0.13 for muscle, 9.09$$pm$$0.49 for adipose tissue, and 0.22$$pm$$0.04 for other organs. With these results, a value of 0.414 for the blood-to-air partition coefficient was calculated by means of our physiologically based pharmacokinetic model. The time variation of radon concentration in mouse blood during exposure to radon was also calculated. All results are compared in detail with those found in the literature.

Journal Articles

Current status of decommissioning activities at Ningyo-toge Environmental Engineering Center

Ishimori, Yuu

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 7 Pages, 2017/04

This paper illustrates the current status of decommissioning activities at four facilities in the Ningyo-toge Environmental Engineering Center of Japan Atomic Energy Agency. (1) The Test milling facility was dismantled from 1999 to 2002. The dismantled materials are stored, and surveyed to determine the quantities of contaminants in the Dismantled materials storage facility. (2) Major equipment at the Refining and conversion facility was dismantled and removed from 2008 to 2013. About 530 t of dismantled materials were generated. Measures of other materials and equipment are taken for easier area managements. (3) A part of centrifuges in the Enrichment engineering facility was decontaminated with 5% of dilute sulfuric acid, and some of them were reused after clearance. Major equipment except centrifuges at the facility has been dismantled and removed since 2014. Dismantling activity will end in 2022. So far, about 270 t of dismantled materials were generated. (4) Centrifuges in the Uranium enrichment demonstration plant have been flushed by $$mathrm{IF}_7$$ gas since 2002 before dismantling. Decontamination efficiencies for DOP-1 and for DOP-2 were about 91% and 99%, respectively. Further plans for dismantling of centrifuges are under review. (5) Related techniques such as measurements are also explained.

148 (Records 1-20 displayed on this page)