Changes of ambient gamma-ray dose rate in Katsushika Ward, metropolitan Tokyo before and after the Fukushima Daiichi Nuclear Power Plant Accident

Katsushika Ward in the eastern part of metropolitan Tokyo was the Tokyo area with the highest deposition of artificial radionuclides after the nuclear accident at the Fukushima Daiichi Nuclear Power Plant. A car-borne survey of the air kerma rate was conducted for all of the ward and the results were compared with measurements done in 2005. The mean air kerma rate in 2014 was 59 ± 12 nGy h⁻¹ and that was 50% higher than the rate in 2005 (p < 0.01). Additionally, the environmental half-life was estimated to be 1.9 years from the transition of ambient equivalent dose rate after the accident for data published by the Katsushika Ward Office

Monthly Precipitation Collected at Hirosaki, Japan: Its Tritium Concentration and Chemical and Stable Isotope Compositions

Monthly precipitation samples were collected at Hirosaki, Aomori Prefecture from January 2018 to December 2020 to measure the ion species and stable hydrogen and oxygen isotope ratios in order to understand the regional properties. The tritium concentration ranged from 0.28 to 1.20 Bq/L, with mean values (±S.D.) of 0.52 ± 0.18, 0.67 ± 0.25 and 0.63 ± 0.21 Bq/L in 2018, 2019 and 2020, respectively. This concentration level was almost the same as for Rokkasho, Aomori Prefecture. The tritium concentration had clear seasonal variation: high in the spring and low in the summer. This trend was thought to arise from seasonal fluctuations in the atmospheric circulation. On the other hand, the pH tended to be low, and the electrical conductivity (EC) tended to be high from the winter to the spring. The ion components, which major ion species contained in sea salt, also tended to be high in the winter, and these components had a strong influence on EC. The d-excess values were high in the winter and low in the summer, and when this trend was considered from the viewpoint of the wind direction data in Hirosaki, these dust components were attributed to the northwest monsoon in the winter to the spring coming from the Asian continent

Concentrations of Chemical Components, Including ^<210>Pb, Present in Aerosols Collected at Naha, Okinawa Prefecture, a Sub-tropical Region of Japan

Aerosol samples were collected at Naha, Okinawa Prefecture, Japan during July 2001 to March 2005 to elucidate the concentrations of chemical components, including ^Pb, present in air for a sub-tropical region of Japan. The NO^-_3, SO^_4, NH^+_4 and Ca^+_2 concentrations had clear seasonal variations and were high in winter to spring and low in summer. ^Pb concentrations ranged from 0.10 to 1.52 mBq m^ and were low in summer and high in the other three seasons. The source of sulfur compounds in the aerosol samples was clarified by combining the sulfur isotope ratio δ^S and ^Pb concentrations. The multi-isotope method using δ^S and ^Pb concentrations was judged to be a good tool for understanding the transported sulfur source

Measurement of Absorbed Dose Rate in Air at NIFS Site after the First Deuterium Plasma Experiment in LHD

The latest measurement of the absorbed dose rate in air was performed at the National Institute for Fusion Science (NIFS) site during the period for the first deuterium plasma experiment conducted in Large Helical Device (LHD). The arithmetic mean of the absorbed dose rates in air for 222 measurement points at the NIFS site was 43 nGy h^. Very little change was observed in the distribution maps of the absorbed dose rates in air before and after the deuterium experiment in the LHD. In addition, the absorbed dose rates in air around the buildings were distributed at similar high levels before and after the deuterium experiment. A radionuclide analysis of soil and broken stone was conducted using a high-purity Ge semiconductor detector. The absorbed dose rates in air at the NIFS site were mainly defined by the radiation from the ground and the building material around the measurement points. The effect of the deuterium experiment was so small that it was undetectable in this study

Development of Rapid Sampling System of Atmospheric Water Vapor for Tritium Measurement

We have developed a rapid sampling system for measuring the tritium in atmospheric water vapor. The system consists of a high-efficiency particulate air filter cartridge, an oil-free compressor, a water-vapor-separating module with hollow fiber membranes, two cold traps, and an oil-free rotary pump. Compressed air (0.4 - 0.7MPa) is introduced into the water-vapor-separation module, which consists of a stainless steel column containing polyimide membrane tubes. Water vapor permeates through the tubes and is collected by cold traps cooled with dry ice and ethanol. The module is heated with a flexible heater to control its temperature. We have determined the recovery yields under various sampling conditions and find that this system can collect atmospheric water vapor with a recovery yield of >99%. This system can thus be a useful tool for understanding short-term observations of tritium in atmospheric water vapor

Absorbed Dose Rate in Air at the NIFS Site before the Deuterium Plasma Experiment in LHD

The absorbed dose rate in air was measured at the National Institute for Fusion Science (NIFS) site before the deuterium plasma experiment in the Large Helical Device (LHD). A pocket survey meter was used for the measurement of 1 cm dose equivalent rates in units of μSv h−1 and these results were converted to absorbed dose rates in air (units: nGy h−1) using a conversion factor. The arithmetic mean of the absorbed dose rates in air based on 257 measurement points at NIFS site was 45 nGy h−1. The result of this study suggests that the building material and/or paving stone enhance the dose rates in air at the NIFS site

IN SITU MEASUREMENT ON THORON EXHALATION RATE IN OKINAWA, JAPAN

INTERNATIONAL WORKSHOP on the ENVIRONMENTAL THORON AND RELATED ISSUE

IN SITU MEASUREMENTS OF THORON EXHALATION RATE IN OKINAWA, JAPAN

INTERNATIONAL WORKSHOP on the ENVIRONMENTAL THORON AND RELATED ISSUE