Temporal and Spatial Variation of Radon Concentrations in Environmental Water from Okinawa Island, Southwestern Part of Japan.

In this study, to get a better understanding in characterizing groundwater and ensure its effective management, the radon concentrations in water samples were measured through Ryukyu limestone in southern Okinawa Island, Japan. Water samples were collected from a limestone cave (Gyokusendo cave, dropping water) and two springs (Ukinju and Komesu, spring water), and the radon concentrations were measured by liquid scintillation counters. The radon concentrations in the samples from the Gyokusendo cave, and Ukinju and Komesu springs were 10 ± 1.3 Bq L-1, 3.2 ± 1.0 Bq L-1, and 3.1 ± 1.1 Bq L-1, respectively. The radon concentrations showed a gradually increasing trend from summer to autumn and decreased during winter. The variation of radon concentrations in the dripping water sample from the Gyokusendo cave showed a lagged response to precipitation changes by approximately 2-3 months. The estimated radon concentrations in the dripping water sample were calculated with the measured radon concentrations from the dripping water obtained during the study period. Based on our results, groundwater in the Gyokusendo cave system was estimated to percolate through the Ryukyu limestone in 7-10 days, and the residence time of groundwater in the soil above Gyokusendo cave was estimated to be approximately 50-80 days. This work makes a valuable contribution to the understanding of groundwater processes in limestone aquifers, which is essential for ensuring groundwater sustainability.

Discriminative Measurement of Absorbed Dose Rates in Air from Natural and Artificial Radionuclides in Namie Town, Fukushima Prefecture.

Ten years have elapsed since the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, and the relative contribution of natural radiation is increasing in Fukushima Prefecture due to the reduced dose of artificial radiation. In order to accurately determine the effective dose of exposure to artificial radiation, it is necessary to evaluate the effective dose of natural as well as artificial components. In this study, we measured the gamma-ray pulse-height distribution over the accessible area of Namie Town, Fukushima Prefecture, and evaluated the annual effective dose of external exposure by distinguishing between natural and artificial radionuclides. The estimated median (range) of absorbed dose rates in air from artificial radionuclides as of 1 April 2020, is 133 (67-511) nGy h-1 in the evacuation order cancellation zone, and 1306 (892-2081) nGy h-1 in the difficult-to-return zone. The median annual effective doses of external exposures from natural and artificial radionuclides were found to be 0.19 and 0.40 mSv in the evacuation order cancellation zone, and 0.25 and 3.9 mSv in the difficult-to-return zone. The latest annual effective dose of external exposure discriminated into natural and artificial radionuclides is expected to be utilized for radiation risk communication.

The Development of an Active Learning Program for the Medical Responders in a Nuclear Disaster.

OBJECTIVE: In Japan, with the revision of the Nuclear Emergency Response Guidelines in 2015, nuclear emergency medical assistance teams responsible for the medical treatment in the acute phase of nuclear disaster have been developed nationwide. The purpose of this research is to develop active learning materials for the education of medical staff, to confirm the educational effect of the materials, and to identify the gaps in nuclear disaster risk reduction in Japan. METHODS: We established a working group and created active learning materials. We trained members of the nuclear emergency medical assistance team using the developed active learning materials and then conducted a questionnaire survey for trainees who participated in the training. RESULTS: Regarding the developed teaching materials, out of 33 trainees, 33 (100%) answered "easy to understand" or "a little understandable" to the item dealing with how to use the radiation detectors and attaching/detaching personal protective equipment. Regarding the simulation about practicing hospital support and medical provision, 3 (8%) answered "a little confusing." CONCLUSION: The study demonstrated that the developed materials have an educational effect. Additionally, the results of the trainee questionnaire showed the necessity for improvement in the triage system and new protocols to help both the patients and responders.

Comparative Study of Performance using Five Different Gamma-ray Spectrometers for Thyroid Monitoring under Nuclear Emergency Situations.

A performance test was carried out using five different gamma-ray spectrometers applicable to thyroid monitoring. The energy resolution and efficiency for 7.6-cm × 7.6-cm NaI(Tl), 5.1-cm × 5.1-cm CeBr3, 3.8-cm × 3.8-cm SrI2(Eu), and 2.5-cm × 2.5-cm SrI2(Eu) gamma-ray scintillation spectrometers and a CdTe gamma-ray semiconductor spectrometer were evaluated using the Oak Ridge Institute for Nuclear Studies thyroid-neck phantom with a mock I source for prompt thyroid monitoring after a nuclear emergency. The respective energy resolutions of the full-energy peak for ~0.360 MeV of 3.8-cm × 3.8-cm SrI2(Eu) and 2.5-cm × 2.5-cm SrI2(Eu) scintillation spectrometers were 4.2% and 4.3%, and these values were very close to the value obtained by the CdTe semiconductor spectrometer. The efficiencies of four of the gamma-ray spectrometers were compared based on the efficiency of the 7.6-cm × 7.6-cm NaI(Tl) scintillation spectrometer at 0 cm from the phantom surface, and these values were ~70% for 5.1-cm × 5.1-cm CeBr3, ~30% for 3.8-cm × 3.8-cm SrI2(Eu), 10% for 2.5-cm × 2.5-cm SrI2(Eu) and 2% for 1-cm × 0.1-cm CdTe. Furthermore, the detection limits at various dose rates for the four gamma-ray scintillation spectrometers were evaluated using the method based on International Organization for Standardization publication ISO 11929:2010.

Measurement system for alpha and beta emitters with continuous air sampling under different exposure situations.

In the present study, a continuous radioactive aerosol measurement system (CRAMS) was developed for measurements of radioactive plume (e.g. 131I, 134Cs and 137Cs) under the emergency situation, and measurements of radon/thoron progeny under the existing situation. As a result, it is suggested that the CRAMS could follow the variation of radon concentration, and the detection limit of the CRAMS under ambient dose equivalent rate of 20µSvh-1, where the temporary evacuation is required within one week in the Japanese regulation, was evaluated to be 129Bqm-3 in the manner of ISO11929.