TRITIUM, HYDROGEN AND OXYGEN ISOTOPE COMPOSITIONS IN MONTHLY PRECIPITATION SAMPLES COLLECTED AT TOKI, JAPAN.

Monthly precipitation samples have been collected at Toki, Japan, from November 2013 to March 2017. In this report, selected data were analysed to identify the regional hydrogen and oxygen isotope compositions. Tritium (3H) concentration in the precipitation ranged from 0.10 to 0.61 Bq L-1 and higher 3H concentrations were observed in spring rather than in other seasons. This range was similar to values reported in Chiba City, Japan. 3H concentration and the ratio d-excess, and δD values were roughly clustered according to each separate season. These regional hydrogen and oxygen isotope compositions will be used for environmental assessments of effects of the deuterium plasma experiments of the large fusion test device.

EVALUATIONS OF INVENTORY AND ACTIVITY CONCENTRATION OF RADIOCESIUM IN SOIL AT A RESIDENTIAL HOUSE 3 YEARS AFTER THE FUKUSHIMA NUCLEAR ACCIDENT.

Soil samples from the surface to a 5 cm depth were collected at a residential house in Koriyama City, Fukushima Prefecture using a scraper plate every three months from March 2014 to September 2014 to evaluate the vertical distribution profiles and inventories of 134Cs and 137Cs in soil. The vertical distribution profiles of radiocesium (134Cs and 137Cs) in soil showed that greater than 86% of the total radiocesium was absorbed in the upper 2 cm 3 years after the accident. Radiocesium in the surface layer seems to move to the lower layer over time. The migration of radiocesium in surface layer might be influenced by the ground surface runoff by rainfall. Radiocesium inventories in June increased significantly over the short period between March and June. In contrast, the radiocesium inventories in September did not increase significantly compared to the values in June. Radiocesium resuspension and deposition caused by decontamination work and meteorological events might be one possible reason for the increased radiocesium inventories observed in June.

RECENT TRITIUM CONCENTRATION OF MONTHLY PRECIPITATION IN JAPAN.

To obtain a better understanding of recent tritium concentration and its seasonal cycle in Japan, monthly precipitation samples were collected in Hokkaido, Gifu and Okinawa prefectures from June 2014 to December 2017. The arithmetic mean ( ± standard deviation) of tritium concentrations in precipitation samples from Hokkaido, Gifu and Okinawa were estimated to be 0.62 ± 0.27 Bq L-1, 0.32 ± 0.12 Bq L-1 and 0.13 ± 0.05 Bq L-1, respectively. These results indicate that the concentrations increase with latitude. In addition, the highest and the lowest concentrations appeared in spring and summer, respectively. To clarify the origins and sources of these cycles, further analyses of chemical compositions of precipitation and meteorological conditions are needed.

CHANGES OF ABSORBED DOSE RATE IN AIR BY CAR-BORNE SURVEY IN NAMIE TOWN, FUKUSHIMA PREFECTURE AFTER THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT.

The latest car-borne survey was carried out by Hirosaki University in order to grasp the local distribution of the absorbed dose rate in air after the evacuation order was lifted on Namie Town in 2017. The car-borne survey of absorbed dose rate in air was carried out on most of the roads which were accessible by car in Namie Town using a 3-in × 3-in NaI(Tl) scintillation spectrometer. The range of the absorbed dose rate in air was calculated to be 0.041-11 µGy h-1. The distribution maps of the absorbed dose rate in air were drawn based on the data obtained during the surveys in 2011, 2015 and 2017. The comparison of these absorbed dose rates in air suggests that the elevated absorbed dose rate in air in Namie Town caused by the FDNPP accident may be decreasing faster than natural decline which includes weathering effect and physical decay due to the artificial decontamination.

Evaluating anthropogenic and environmental tritium effects using precipitation and Hokkaido snowpack at selected coastal locations in Asia.

Tritium dating requires a good understanding of the tritium and water inputs into hydrologic systems, including their main trends due to latitudinal, seasonal and altitudinal effects. Although tritium reached ambient levels at the end of the 20th century, tritium released from nuclear facilities and bomb tests since then has the potential to confound use of tritium for age dating. We therefore collected precipitation and snowpack samples for tritium analysis to confirm that tritium levels in Japanese precipitation had not exceeded ambient levels following the North Korean nuclear tests in January 6th 2016 and September 3rd 2017. As the result, the highest tritium concentration was 5.52(±0.27)TU at samples collected from January 8 to 11th at one Honshu and four Hokkaido locations and samples collected at six Honshu locations had 8.01(±1.5)TU from September 6 to 19th 2017. Confirming ambient tritium concentrations after both events we investigated the latitude tritium effect at selected coastal stations in Asia, indicating a break of latitude trend around Tokyo area, and established the latitude scaling factors to the north and south of the Tokyo area data. The seasonal trend was investigated during the winter-spring 2016 in precipitation samples confirming the higher spring tritium compared with winter continental tritium values. The altitude effect on tritium and stable (18O and 2H) isotopes was observed in Hokkaido snowpack, which had tritium concentrations ranging between 4.08 and 5.93 TU during March-April, and demonstrated two trends for western and central Hokkaido mountain ranges. Using established latitude and altitude scaling factors with the long-term continuous time-series of monthly Tokyo area tritium we estimated the annual weighted tritium at 110 meteorological stations in Japan with monthly precipitation demonstrating the applicability of this approach for future tritium-tracer studies across Asia.

Terrestrial gamma radiation dose rate in Ryukyu Islands, subtropical region of Japan.

In order to explain the distribution of natural radiation level in the Asia, in situ measurements of dose rate in air due to terrestrial gamma radiation have been conducted in a total of 21 islands that belong to Ryukyu Islands (Ryukyu Archipelago), subtropical rejoin of southwest Japan. Car-borne surveys have also been carried out in Okinawa-jima, the biggest island of the archipelago. Based on the results for these measurements, arithmetic mean, the maximum and the minimum of the dose rates at 1 m in height from the unpaved soil ground in the archipelago were estimated to be 47, 165 and 8 nGy h(-1), respectively. A comparative study of car-borne data obtained prior to and subsequent to the 2011 Fukushima nuclear accident, as for Okinawa-jima, indicated that the nuclear accident has no impact on the environmental radiation at the present time.

FWT and OBT concentrations in pine needle samples collected at Toki, Japan (1998-2012).

Free water tritium (FWT) and organically bound tritium (OBT) concentrations in pine needles have been investigated to understand the regional background tritium concentration in Toki City. Samples were regularly collected from pine trees on the National Institute for Fusion Science campus (1998-2012) and the nearby Shiomi Park (SP; 2002-12). FWT and OBT concentrations of the former samples ranged from 0.33 to 0.92 and 0.41 to 1.10 Bq l(-1), respectively, while those of the latter samples ranged from 0.32 to 0.86 and 0.33 to 0.79 Bq l(-1), respectively. Results of both sampling sites were almost the same, and they have been gradually decreased year by year. Concentration level of tritium for Toki City was close to the average background level in Japan. The OBT/FWT ratios were almost 1.0. The apparent half-life of FWT in this period was estimated as almost 10 y, and that of OBT was estimated as almost 12 y; these values were almost the same as the physical half-life.

Comparative dosimetry for radon and thoron in high background radiation areas in China.

The present study focuses on internal exposure caused by the inhalation of radon and thoron progenies because the internal exposures have not yet been clarified. For their dose assessment, radon, thoron and thoron progeny concentrations were measured by passive monitors over a long period (for 6 months). Consequently, radon, thoron and equilibrium equivalent thoron concentrations were given as 124 ± 78, 1247 ± 1189 and 7.8 ± 9.1 Bq m(-3), respectively. Annual effective doses are estimated to be 3.1 ± 2.0 mSv for radon and 2.2 ± 2.5 mSv for thoron. Total dose are estimated to be 5.3 ± 3.5 mSv a(-1). The present study has revealed that the radon dose was comparable with the thoron dose, and the total dose was ∼2 times higher than the worldwide average.

[Measurement of functional residual capacity by nitrogen washout during mechanical ventilation].

A medical gas analyzer AMIS 2000 SP, which is a mass spectrometer, incorporating a fractional residual capacity (FRC) measuring program based on a nitrogen washout method, has been introduced recently. The purpose of this study was to assess the reliability and the reproductivity of the FRC measuring system in a clinical situation. FRC was measured by this system connected to a ventilator (Bennet 7200ae). Our study examined; 1) the accuracy of the measurement using a syringe. 2) the difference in two consecutive measurements in the same subject during mechanical ventilation, and 3) the correlation between the measured and the predicted value calculated with Gorldman's formula in 18 subjects during ventilation. The first study has showed an excellent correlation (y = 0.953x + 0.092, r = 0.996, P < 0.001) or y = 0.909x + 0.132 (r = 0.999, P < 0.001) with a tidal volume of 400 ml or 500 ml, respectively) between the measured value and the syringe capacity. Reproductivity was proved by the linear regression (y = 0.977x + 0.024, r = 0.998, P < 0.001) between the two consecutive measurements. A good correlation was shown between the measured values and the predicted values (y = 0.656x - 0.415, r = 0.849, P < 0.0001). These results showed good reliability and reproductivity of our FRC measuring system. It is concluded that the FRC measurements using AMIS2000SP system can be used in clinical respiratory managements in ICU.