Radiation research trends by young scientists and the future tasks in Northern Japan: report on 'the 10th educational symposium on radiation and health (ESRAH) by young scientists in 2023'.

PURPOSE: Since 2014, an educational activity on radiation and health in northern Japan has been carried out by young scientists, the so-called 'Educational Symposium on Radiation and Health (ESRAH)'. Close cooperation has been continued in preparing for any possible emergency response to radiation accidents because several facilities, e.g., the Tomari Nuclear Power Plant in Hokkaido and the Low-Level Radioactive Waste Disposal Facility in Aomori prefecture. The ESRAH meeting has provided informational exchange and discussion forum on a broad range of subjects in various. In 2023, the 10th Memorial ESRAH meeting took place to boost scientific understanding and multidisciplinary collaborations for young scientists. Herein, we report on the ESRAH2023 symposium and analyze the research categories of young scientists from the past 10-year presentations. CONCLUSIONS: To date, the ESRAH meeting has successfully provided a chance for multi-disciplinary research, which accounted for 27% of the total despite the COVID-19 pandemic. We found that the fraction of multi-disciplinary research in 2023 was the highest during 10-year ESRAH meetings. Meanwhile, amongst the research categories, physics, chemistry, and pharmacological studies were indicated to be less for young scientists. It is desired that further collaboration between physics, chemistry, and pharmacology in addition to the current fields would not only clarify radiation effects on the human body but also promote emergency medical care for radiation exposure in the future.

Thoron exposure in the radon-thoron prone area of the Adamawa Region, Cameroon.

The radon-prone area of the Adamawa region is characterized by high radon concentrations, where no low-risk area was observed. This study aims to investigate about indoor thoron concentration in this area, using RADUET detectors, thoron progeny monitors and DTPS/DRPS. The indoor thoron concentration ranged between 17 and 1000 Bq m-3, with an average of 131 Bq m-3. 36% of dwellings have thoron concentration less than 100 Bq m-3 while 28% are above 300 Bq m-3. The thoron equilibrium factor of 0.04 was found to be two times higher than the globally assumed value. Thoron progeny contributes on average to 26% (1.9 mSv y-1) of the total inhalation dose. The excess lifetime cancer risk due to thoron progeny is about 5%. These results justify that thoron cannot be neglected when assessing radiation doses. As only radon is regulated, such study will contribute to accelerate the regulation on thoron.

Effective dose assessment due to inhalation of 222Rn, 220Rn, and their progeny: highlighting the major contribution of thoron in a thoron-prone area in Cameroon.

To assess public exposure to radon, thoron, and their progeny, measurements were conducted in 50 dwellings within the bauxite-rich area of Fongo-Tongo in western Cameroon. Passive integrating radon-thoron discriminative detectors (specifically RADUET) were employed for radon and thoron measurements. Additionally, concentrations of short-lived radon and thoron progeny were estimated using Direct Radon Progeny Sensors (DRPSs) and Direct Thoron Progeny Sensors (DTPSs) based on LR-115 detectors. The findings revealed indoor radon concentrations ranging from 31 to 123 Bq m-3 with a geometric mean (GM) of 62 Bq m-3, and indoor thoron concentrations ranging from 36 to 688 Bq m-3 with a GM of 242 Bq m-3. The Equilibrium Equivalent Radon Concentration (EERC) ranged from 3 to 86 Bq m-3 with a GM of 25 Bq m-3, while the Equilibrium Equivalent Thoron Concentration (EETC) ranged from 1.2 to 12.5 Bq m-3 with a GM of 7.6 Bq m-3. Notably, all dwellings recorded radon concentrations below 100 Bq m-3. Arithmetic means of radon and thoron equilibrium factors were calculated as 0.47 and 0.04, respectively. To assess annual effective doses from radon and thoron inhalation, equilibrium factors were used along with direct measurements of EERC and EETC. The differences observed in annual effective doses were 4.5% for radon and 42.5% for thoron. Furthermore, the contribution of thoron and its decay products to the annual effective dose from radon, thoron, and their progeny ranged from 12 to 94%, with an average contribution of 58%. Thus, this study found that the effective dose due to thoron inhalation in the study area exceeded that due to radon inhalation. It is concluded that, when evaluating radiation doses and health risks, it is crucial to consider both thoron and its progeny alongside radon and its progeny. This underscores the importance of considering direct measurements for accurately estimating radiation doses.

Health Impacts of Natural Background Radiation in High Air Pollution Area of Thailand.

Chiang Mai province of Thailand is known for having the highest natural background radiation in the country, as well as being recognized as one of the world's most polluted cities for air quality. This represents the major contributor to the development of lung cancer. This research aims to estimate the comprehensive dose of both internal and external exposure due to natural background radiation and related health perspectives in the highly polluted area of Chiang Mai. The average values of indoor radon and thoron concentrations in 99 houses over 6 months were 40.8 ± 22.6 and 17.8 ± 16.3 Bq/m3, respectively. These results exceed the worldwide value for indoor radon and thoron (40 and 10 Bq/m3), respectively. During burning season, the average values of indoor radon (56.7 ± 20 Bq/m3) and thoron (20.8 ± 20.4 Bq/m3) concentrations were higher than the world-wide averages. The radon concentration in drinking water (56 samples) varied from 0.1 to 91.9 Bq/L, with an average value of 9.1 ± 22.8 Bq/L. Most of the drinking water samples (87%) fell below the recommended maximum contamination limit of 11.1 Bq/L. The average values of natural radionuclide (226Ra, 232Th and 40K) in 48 soil samples were 47 ± 20.9, 77.9 ± 29.7 and 700.1 ± 233 Bq/kg, respectively. All values were higher than the worldwide average of 35, 30 and 400 Bq/kg, respectively. The average value of outdoor absorbed gamma dose rate (98 ± 32.5 nGy/h) exceeded the worldwide average of 59 nGy/h. Meanwhile, the average activity concentrations of 226Ra, 232Th and 40K in 25 plant food samples were 2.7 ± 0.1, 3.2 ± 1.6 and 1000.7 ± 1.9 Bq/kg, respectively. The 40K concentration was the most predominant in plant foods. The highest concentrations of 226Ra, 232Th and 40K were found in Chinese cabbage, celery and cilantro, respectively. The total annual effective dose for residents in the study area varied from 0.6 to 4.3 mSv, with an average value of 1.4 mSv. This indicates a significant long-term public health hazard due to natural background radiation and suggests a heightened radiation risk for the residents. The excess lifetime cancer risk value (5.4) associated with natural background radiation was found to be higher than the recommended value. Moreover, the number of lung cancer cases per year per million average of 25.2 per million persons per year was in the limit range 170-230 per million people. Overall, our results will be used for future decision making in the prevention of lung cancer risk associated with natural background radiation.

Simultaneous measurements of radon, thoron and thoron progeny and induced cancer risk assessment in Djeno, Pointe-Noire, Republic of Congo.

In this study, the activity concentrations of radon (222Rn), thoron (220Rn) and thoron progeny were measured simultaneously in Djeno (Pointe-Noire, Republic of Congo) using RADUET detectors to evaluate the air quality and the radiological risks due to the inhalation of these radionuclides. Activity concentrations of radon progeny were calculated from those of radon. Indoor radon, thoron and progenies followed a lognormal distribution ranging between 20 and 40, 6 and 62, 8 and 17.6 and 0.4 and 19.6 Bq m-3 for radon, thoron, radon progeny and thoron progeny, respectively. Mean values for radon were lower than the worldwide values estimated by the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which are 40 Bq m-3 (arithmetic mean) and 45 Bq m-3 (geometric mean). Radon concentrations in the dwellings under study were below the World Health Organization and the International Commission on Radiological Protection recommended reference levels, which are, respectively, 100 and 300 Bq m-3. The mean concentration of thoron was twice the world average value of 10 Bq m-3 estimated by UNSCEAR. Thoron progeny mean concentration was sharply greater than the typical value (0.3 Bq m-3) for indoor atmosphere provided by UNSCEAR. Annual effective dose ranges were 0.40-0.87 mSv (arithmetic mean, 0.57 ± 0.11 mSv) for radon and 0.10-4.14 mSv (arithmetic mean, 0.55 ± 0.77 mSv) for thoron. The mean value for radon was lower than the value (1.15 mSv) estimated by UNSCEAR, while the mean value for thoron was five times higher than the UNSCEAR value (0.10 mSv). The study showed that the use of the typical equilibrium factor value given by UNSCEAR to compute effective dose led to an error above 80%. Finally, the results of this study showed that the excess relative risk of radon-induced cancer was low, below 2% for the population under 55 y. The results presented in the present study prove that the population of Djeno is exposed to a relatively low potential risk of radon- and thoron-induced cancer.

Site-specific dose conversion factors for radon progeny based on ambient aerosol characteristics in an outdoor environment and a tourist cave.

Site-specific Dose Conversion Factors (DCFs) for radon progeny were estimated based on the aerosol measurement results in an outdoor environment and a tourist cave. The Activity Median Diameter (AMD) and unattached fraction were measured and used to calculate the effective dose per unit intake of radon progeny. The AMDs in the outdoor environment was in the range of 0.24-0.71 µm with the unattached fraction of 0.17. In the tourist cave, two peaks were found in the aerosol size distribution at nucleation and accumulation modes and the unattached fraction was measured to be 0.69 with a range of 0.36-0.85. The DCFs at the outdoor environment did not differ from those from the publication of the International Commission on Radiological Protection; however, the DCF in the tourist cave was significantly higher due to the discrepancy in the unattached fraction and the aerosol size distribution. It was found that these two factors would significantly affect the DCF so that we should be aware of it.

Calibration experiments for radon in drinking water measurements using portable-type electrostatic-collection radon monitors.

Portable-type electrostatic-collection radon monitors (RAD7) are often used for in-situ measurements of radon in water. In this study, we evaluated the calibration factors and their uncertainties for two RAD7 monitors based on comparative measurements with the liquid scintillation counting method. In the first experiment, we found that both RAD7 monitors had relatively large uncertainties due to leakage of radon gas that bubbled from the gaps between the lids of the desiccant container and the glass vial. Therefore, for the second experiment, these gaps were closed as much as possible using parafilm and clay, respectively. As a result, the relative uncertainties for both RAD7 monitors were significantly decreased. Furthermore, we collected spring water samples to confirm the reliability of radon concentrations. After closing the leakage point, the uncertainty of radon concentrations in spring water we measured using the typical protocol of the RAD7 were significantly lower, which improves the measurement.

Mapping in a radon-prone area in Adamawa region, Cameroon, by measurement of radon activity concentration in soil.

The radon-prone area of the Adamawa region in Cameroon is characterized by high natural radiation background resulting from the high concentrations of radium-226, thorium-232, and indoor radon. To produce a radon-risk map, radon measurements in soil were carried out in the city of Ngaoundere. The radon activity concentration in soil gas ranged from 256 to 166 kBq m-3 with a mean of 80 kBq m-3 and a standard deviation of 38 kBq m-3. The area is mostly classified as high risk (80%) according to the Swedish classification, and 20% as medium risk. A low-risk area was not observed. Granite-like geology sites were characterized by higher radon concentration. A ratio of about 295:1 was obtained for soil radon gas to indoor radon concentrations, with a positive correlation (R = 0.40), and a transfer factor of 3 per mil. These results demonstrate that in situ measurements of radon concentration in soil can provide accurate information on the level of indoor radon concentrations. Geostatistical and deterministic interpolation techniques have been used to obtain a radon map by comparing the suitability of ordinary kriging and inverse-distance-weighted (IDW) interpolation methods. It turned out that there is not much difference in the prediction errors of the two techniques (Root Mean Square Error = 34.4 for ordinary kriging and 34.3 for IDW). It is concluded that both methods give acceptable results. In situ measurements and geostatistical analysis allow assessment of expected indoor radon exposure in a given area at reduced costs and time required. However, for the investigated area, more research is needed to produce reliable radon-risk maps.

Car-borne survey and dose assessment from external radiation exposure in Bangka Island.

With a history of more than 200 years of tin mining, Bangka Island has brought along a byproduct of heavy minerals containing radionuclide elements. There are some concerns about this byproduct material contributing to natural radiation in the environment. In this study, a car-borne survey was conducted to accurately assess natural background radiation in Bangka Island. Indoor and outdoor ambient dose rates in 146 houses were also measured to assess the radiation dose from external exposure received by the public. Soil samples were collected and measured using a gamma spectroscopy system to evaluate the contributions of specific radionuclides to external terrestrial exposure. From 3790 measurement points during the car-borne survey, the highest ambient dose equivalent rate was 596 nSv h-1 measured in Muntok area, with a mean value of 101 nSv h-1 and a median value of 95 nSv h-1. The ambient dose equivalent rate distribution map showed a relatively higher value in the northern coastal area of the island, where the Pemali tin deposit is located. The annual effective dose received from external radiation in the 146 houses in Bangka Island ranged from 0.44 to 1.30 mSv year-1, with a median value of 0.66 mSv year-1. The soil contained a relatively high amount of thorium (232Th), which contributed 69% to external radiation exposure in Bangka Island.

Residential radon exposure in Astana and Aqsu, Kazakhstan.

A pilot study was carried out to measure indoor radon concentrations in a uranium mining area of northern Kazakhstan. A total of 80 places at kindergartens, elementary schools, and dwellings were selected in Aqsu village and Astana city as the uranium mining area and background area for comparison, respectively. In Astana and Aqsu, the 3-month radon concentrations from late summer to autumn in 2022 were measured using the RADUET passive radon detectors. Radon concentrations ranged from 4 to >2000 Bq m-3(mean ± standard deviation: 290 ± 173 Bq m-3) throughout the study areas. The concentrations were higher in Aqsu, and 70% of the dwellings there exceeded 300 Bq m-3, whereas only 5% of them exceeded 300 Bq m-3in Astana. Accordingly, the new dose conversion factor for radon recommended by International Commission on Radiological Protection Publication 137 was applied to calculate the annual effective dose. The annual effective dose from the inhalation of radon was estimated to be 3.6 ± 4.6 mSv y-1for Astana and 23.7 ± 15.6 mSv y-1, for Aqsu, which are both higher than the world average value of 2.5 mSv y-1.

Estimation of Ambient Dose Equivalent Rate Distribution Map Using Walking Survey Technique in Hirosaki City, Aomori, Japan.

At present, much emphasis is placed on the health risks associated with radioactivity present in the environment, especially since the accident at the Fukushima Daiichi Nuclear Power Plant. In this study, a walking survey was conducted in Hirosaki City using a NaI(Tl) scintillation spectrometer to estimate and map the distribution of the ambient dose equivalent rate to monitor the radiological safety of the general public in Hirosaki City, where many nuclear facilities are located nearby. The average (±standard deviation) ambient dose equivalent rate was 0.056 ± 0.020 µSv h-1. By comparison with the measurement data, it was found that the values of 85% of the data obtained using the walking survey technique deviated within ±20% relative to those obtained by spot measurements. Furthermore, the distribution of dose rates obtained in the nighttime survey was not significantly different from those obtained in the daytime.

INFLUENCE OF SAMPLING FLOW RATE ON THORON EXHALATION RATE MEASUREMENTS BY THE CIRCULATION METHOD.

Researchers have used various methods to obtain the exhalation rates of radon and thoron from soil and building materials. One of the typical methods for radon exhalation rate is the circulation method using an accumulation container, an external or internal sampling pump and a continuous radon monitor. However, it is necessary to consider sampling flow rate if this method is applied to exhalation rate measurement for thoron due to its short half-life. Based on a calibration experiment, the measured thoron concentrations obtained by an electrostatic collection type radon and thoron monitor (RAD7) were found to be influenced strongly by the sampling flow rate. It was also found that the thoron exhalation rate from a soil sample depended on the pressure difference which was proportional to the increasing sampling flow rate. The thoron exhalation rate measured at the generally used sampling flow rate of the internal sampling pump of the RAD7 was overestimated compared with the value at 0 L min-1.

PERFORMANCE EVALUATION OF COMMERCIAL SCINTILLATION COCKTAILS FOR LOW-LEVEL TRITIUM COUNTING BY HIGH-CAPACITY LIQUID SCINTILLATION COUNTER.

Low-background liquid scintillation counter is one of the popular measuring instruments used to investigate tritium radioactivity in environmental media. These instruments require the liquid sample and organic solvent to be mixed for tritium measurement. In the European Union, the registration, evaluation, authorization and restriction of chemicals regulation was established to control the use of chemical substances of very high concern. It is important to find continuously available alternative reagents. In this paper, a performance evaluation was conducted using four scintillation cocktails according to Japanese conventional procedure; although one of them, Gold Star LT2, contains nonylphenol ethoxylate, it will continue to be available for research and development. From the evaluation results it was confirmed that Gold Star LT2 would be a satisfactory alternative scintillator, which is similar performance of Ultima Gold LLT.

INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND.

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0 mSv, respectively, and as 5.9-9.0 mSv in total.

222Rn and 226Ra Concentrations in Spring Water and Their Dose Assessment Due to Ingestion Intake.

222Rn and 226Ra concentrations of less than a few to several thousands of Bq L-1 have been observed in several underground bodies of water around the world. Although regulations for these concentrations in water have been implemented internationally, there are currently no regulations in place in Japan. However, concentrations that exceed these internationally recognized regulatory values have also been observed in Japan. In this study, concentrations in spring water in the northern part of Japan were measured and the effective dose from intake of the water was evaluated. 222Rn concentrations were measured using a liquid scintillation counter, and 226Ra concentrations were measured using a high purity germanium detector after chemical preparation. The measured 222Rn concentrations (=12.7 ± 6.1 Bq L-1) and 226Ra concentrations (<0.019-0.022 Bq L-1) did not exceed the reference values set by international and European/American organizations. A conservative estimate of the annual effective ingestion dose of 8 µSv for 222Rn and 226Ra obtained in this study is much smaller than the estimated overall annual effective dose of 2.2 mSv from natural radiation to the Japanese population. However, this dosage accounts for 8% of the WHO individual dosing criteria of 0.1 mSv/year for drinking water.

Heavy Metal Assessments of Soil Samples from a High Natural Background Radiation Area, Indonesia.

Mamuju, Indonesia, is an area with high natural background radiation. This study assesses heavy metal content in soil samples from this area to determine the level of public and environmental hazard it presents. This study analyzes natural radionuclide elements using high purity germanium (HPGe) gamma spectrometry and performs heavy metals analysis using a flame atomic absorption spectrometry (FAAS). Moreover, pollution indices and descriptive analyses were used to assess heavy metal contamination in the environment and the correlation between heavy metals and radionuclides. The results demonstrate that soil samples in several areas of Mamuju contain a high concentration of the natural radionuclides 226Ra and 232Th, and that heavy metal concentrations in the soil decrease in the sequence Zn > Pb > Cr > Cu > Ni > Cd. This study revealed that soil samples from Mamuju are moderately contaminated. There was a strong positive relationship between 226Ra, 232Th, ambient dose equivalent rate, and Pb. Ecological risk index (RI) and cumulative pollution index (IPI) values in Mamuju are 2.05 and 125, respectively, which are possible hazards to human health as a result. Pb concentration in the Mamuju soil samples ranged from 109 to 744 mg kg-1, exceeding the worldwide average of 27 mg kg-1.

RADON AND THORON EXHALATION RATES FROM EARTHEN BUILDING MATERIALS USED IN HIGH BACKGROUND RADIATION AREAS OF HOMA AND RURI, KENYA.

222Rn and 220Rn surface exhalation rates from earthen building materials used in high background radiation areas of Homa and Ruri, Kenya have been measured using an accumulation chamber coupled with RAD7 detector. Activity concentrations of 226Ra and 232Th in the building materials were determined by γ-ray spectroscopy. In Homa the average 222Rn surface exhalation was 1 ± 0.1 mBqm-2 s-1, while that of 220Rn was 18 ± 2 Bqm-2 s-1; in Ruri 222Rn was 0.9 ± 0.1 mBqm-2 s-1 and 220Rn was 25 ± 3 Bqm-2 s-1. 222Rn was 26 times lower than world average and 220Rn was higher by a factor of 21. Average 232Th in Ruri was 1094 ± 55 Bq/kg, three times that in Homa; 226Ra was 129 ± 10 and 111 ± 6 Bq/kg in Homa and Ruri, respectively. There was a strong correlation between exhalation rate of 222Rn and concentration of 226Ra, as well as between 232Th and 220Rn. Thus, 220Rn was the major contributor to the inhaled dose in earthen dwellings of the two regions.

Long-Term Measurements of Radon and Thoron Exhalation Rates from the Ground Using the Vertical Distributions of Their Activity Concentrations.

A long-term measurement technique of radon exhalation rate was previously developed using a passive type radon and thoron discriminative monitor and a ventilated type accumulation chamber. In the present study, this technique was applied to evaluate the thoron exhalation rate as well, and long-term measurements of radon and thoron exhalation rates were conducted for four years in Gifu Prefecture. The ventilated type accumulation chamber (0.8 × 0.8 × 1.0 m3) with an open bottom was embedded 15 cm into the ground. The vertical distributions of radon and thoron activity concentrations from the ground were obtained using passive type radon-thoron discriminative monitors (RADUETs). The RADUETs were placed at 1, 3, 10, 30, and 80 cm above the ground inside the accumulation chamber. The measurements were conducted from autumn 2014 to autumn 2018. These long-term results were found to be in good agreement with the values obtained by another methodology. The radon exhalation rates from the ground showed a clearly seasonal variation. Similar to findings of previous studies, radon exhalation rates from summer to autumn were relatively higher than those from winter to spring. In contrast, thoron exhalation rates were not found to show seasonal variation.

Radon Activity Concentrations in Natural Hot Spring Water: Dose Assessment and Health Perspective.

The world community has long used natural hot springs for tourist and medicinal purposes. In Indonesia, the province of West Java, which is naturally surrounded by volcanoes, is the main destination for hot spring tourism. This paper is the first report on radon measurements in tourism natural hot spring water in Indonesia as part of radiation protection for public health. The purpose of this paper is to study the contribution of radon doses from natural hot spring water and thereby facilitate radiation protection for public health. A total of 18 water samples were measured with an electrostatic collection type radon monitor (RAD7, Durridge Co., USA). The concentration of radon in natural hot spring water samples in the West Java region, Indonesia ranges from 0.26 to 31 Bq L-1. An estimate of the annual effective dose in the natural hot spring water area ranges from 0.51 to 0.71 mSv with a mean of 0.60 mSv for workers. Meanwhile, the annual effective dose for the public ranges from 0.10 to 0.14 mSv with an average of 0.12 mSv. This value is within the range of the average committed effective dose from inhalation and terrestrial radiation for the general public, 1.7 mSv annually.

A simple technique for measuring the activity size distribution of radon and thoron progeny aerosols.

In this study, a portable cascade impactor was developed to more efficiently determine the activity size distribution of attached radon and thoron progeny in a natural environment. The developed impactor consisted of four stages with a backup filter stage for collection of the aerosol samples. The aerosol cut points were set for 10, 2.5, 1, and 0.5 µm at a sampling rate of 4 L min-1. Five CR-39 chips were used as alpha detectors for each stage. To separate the alpha particles emitted from radon and thoron progeny, the CR-39 detectors were covered with aluminium-vaporized Mylar films. The thickness of each film was adjusted to allow alpha particles emitted from radon and thoron progeny to reach the surface of the CR-39 detectors. The particle cut-off characteristics of each stage were determined by mono-dispersive aerosols with particle sizes ranging from 0.1 to 1.23 µm from the collection efficiency curve. The test results showed that the respective cut-off size of stages 3 and 4 were close to the designed cut-points. Validation of the technique by comparison with two commercial devices confirmed that the developed technique could provide the necessary information to estimate the activity size distribution of attached radon and thoron progeny for dose assessment, especially, in a field survey where direct electric power is not available.