ACTIVITY RATIO OF URANIUM IN FUKUSHIMA SOIL SAMPLES USING MULTI-COLLECTOR INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY.

The Fukushima soils have been collected from Namie and Futaba areas for the radiocaesium and uranium isotope ratio studies. The 137Cs activity concentration of soil samples ranged from 6 ± 1 to 756 ± 14 kBq/kg. The uranium isotope ratios are measured using multi collector inductively coupled plasma mass spectrometry.

Comparison experiments for radon and thoron measuring instruments at low-level concentrations in one room of a Japanese concrete building.

A comparison on commercially available radon (Rn) measuring instruments (three types of continuous monitors and a passive Rn-thoron (Rn) discriminative alpha track detector) was carried out at low-level concentrations in one room of a concrete building. The agreements between the continuous monitors were within 15%, while the agreements between each instrument were within 20%. It was also observed that the indoor Rn concentration measured by the continuous monitor was quite different from those by the passive detectors due to the mean concentration less than the limit of detection of both measuring instruments.

Sorption-desorption coefficients of uranium in contaminated soils collected around Fukushima Daiichi Nuclear Power Station.

Various radionuclides including fission products and heavy nuclides were released into the environment during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The dissolution followed by migration of deposited radionuclides of Cs, Sr and U on soils could take place to the local environment. Therefore, it is necessary to determine sorption-desorption coefficients of U in soil-water system around the FDNPS from a migration viewpoint.

Measurement of uranium isotope ratios in Fukushima-accident contaminated soil samples using multi collector inductively coupled plasma mass spectrometry.

In the present study, Cs and U activity concentrations, U/U activity ratio, and U/U isotope ratio were measured in fifteen soil samples collected from the exclusion zone around the Fukushima Daiichi Nuclear Power Station (FDNPS). The Cs activity concentrations of Fukushima-accident contaminated soil samples ranged from 29.9 to 4780 kBq kg with a mean of 2007 kBq kg.

Gamma dose rate distribution in the Unegt subbasin, a uranium deposit area in Dornogobi Province, southeastern Mongolia.

Unegt subbasin in Dornogobi Province, southeastern Mongolia, contains the Dulaan Uul uranium deposit, for which development for commercial mining has been conducted as of 2015. Zuunbayan is a commune located close to the Dulaan Uul uranium deposit, and residents of Zuunbayan and their livestock can easily approach the uranium deposit area, including an aboveground dump site, which was created as a result of the mining development. The present study measured and analyzed the gamma dose rate (absorbed dose rate in air) distribution in Unegt subbasin using data collected from a car-borne measurement survey.

CHARACTERISTICS OF INDOOR RADON AND THORON CONCENTRATIONS IN CAVE DWELLINGS IN GANSU PROVINCE, CHINA.

Short-term measurements were made in four different types of Chinese cave dwellings, 'ground', 'open-cut', 'aboveground' and 'underground', located in Gansu Province, China, in order to evaluate the diurnal and seasonal variations in indoor radon (222Rn) and thoron (220Rn) concentrations. As a result, in most of the 'ground' and 'open-cut' cave dwellings in summer, the indoor 222Rn concentrations during the nighttime were higher than those during the daytime. In the winter, such fluctuation was not observed.

REDUCTION IN AMBIENT GAMMA DOSE RATE FROM RADIOCESIUM DUE TO SNOW COVER.

In the present study, variations in ambient gamma dose rate associated with snow cover were examined in a radioactive-contaminated site in Fukushima Prefecture, Japan. The ambient gamma dose rates decreased with increasing snow depth. The reduction trends were different between fresh snow (0.

Fungal spore involvement in the resuspension of radiocaesium in summer.

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10 to 10 Bq per m and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied.

Pu/Pu activity ratio as an indicator of Pu originating from the FDNPP accident in the terrestrial environment of Fukushima Prefecture.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident has caused significant radionuclide contamination. Pu isotopes at the level of GBq were released from the damaged reactors to terrestrial and marine ecosystems. In this work, 35 samples were collected at different locations of Fukushima.

DISTRIBUTIONS OF INDOOR GAMMA DOSE RATES IN RELATION TO GAMMA-RAY EMISSIONS FROM BUILDING MATERIALS: CASE STUDY OF HIGH-RISE CONCRETE BUILDING IN FUKUSHIMA.

The spatial distribution of ambient gamma dose rates in a high-rise steel-reinforced concrete building in Fukushima, Japan, was examined relative to the gamma-ray emissions from building materials and radionuclides derived from the 2011 nuclear accident. The results revealed the minor role of accident-derived radionuclides in ambient gamma dose rates ~7 y after the accident. The ambient gamma dose rates were higher in the upper floors because of gamma-ray emissions from natural radionuclides in the floor slabs.

ELEVATION OF GAMMA DOSE RATE BY CONSTRUCTION OF THE ASIAN HIGHWAY 3 (AH3) BETWEEN ULAANBAATAR AND SAINSHAND, MONGOLIA.

The present study aimed at examining changes of gamma radiation level associated with road construction in Mongolia. A car-borne survey of gamma dose rate was made for a paved, ~450-km long part of the Asian Highway 3 between Ulaanbaatar and Sainshand. The gamma dose rates ranged from 48 to 173 nGy/h.

Radiation dose due to radon and thoron progeny inhalation in high-level natural radiation areas of Kerala, India.

In order to evaluate internal exposure to radon and thoron, concentrations for radon, thoron, and thoron progeny were measured for 259 dwellings located in high background radiation areas (HBRAs, outdoor external dose: 3-5 mGy y) and low background radiation areas (control areas, outdoor external dose: 1 mGy y) in Karunagappally Taluk, Kerala, India. The measurements were conducted using passive-type radon-thoron detectors and thoron progeny detectors over two six-month measurement periods from June 2010 to June 2011. The results showed no major differences in radon and thoron progeny concentrations between the HBRAs and the control areas.

NATURAL RADIOACTIVITY LEVEL AND ELEMENTAL COMPOSITION OF SOIL SAMPLES FROM A HIGH BACKGROUND RADIATION AREA ON EASTERN COAST OF INDIA (ODISHA).

A comprehensive study was carried out to determine the radioactivity concentration of soil samples from different sites of a high background radiation area in the eastern coast of India, Odisha state. The dose rate measured in situ varied from 0.25 to 1.

Long-term measurements of residential radon, thoron, and thoron progeny concentrations around the Chhatrapur placer deposit, a high background radiation area in Odisha, India.

The Chhatrapur placer deposit is found in a high background radiation area which has been recently identified on the southeastern coast of India. Previously, some geochemical studies of this area were carried out to assess external dose from radionuclides-bearing heavy mineral sands. In this study, radon, thoron and thoron progeny concentrations were measured in about 100 dwellings during three seasons (autumn-winter, summer, and rainy) in a 10- to 12-month period and annual doses due to inhalation of them were evaluated.

Strontium-90 activity concentration in soil samples from the exclusion zone of the Fukushima daiichi nuclear power plant.

The radioactive fission product (90)Sr has a long biological half-life (˜18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Assessing (90)Sr is therefore extremely important in case of a nuclear disaster.

Radiation survey on Fukushima Medical University premises about four years after the Fukushima nuclear disaster.

This study was conducted on the Fukushima Medical University (FMU) premises (in Fukushima City, Fukushima Prefecture) about four years after the Fukushima Daiichi Nuclear Power Plant accident.　Its objectives were (1) to create a map of the ambient gamma dose rate (air-kerma rate) distribution, (2) to evaluate the air-kerma rate originating from natural radionuclides, and (3) to investigate the effects of snow cover on changes in the air-kerma rate.　This man-borne survey revealed that the air-kerma rate varies widely, ranging from 0.

An intercomparison done at NIRS, Japan on continuous monitors for measuring ²²⁰Rn concentration.

An intercomparison for continuous monitors that measure thoron ((220)Rn) concentration was carried out using a (220)Rn chamber of National Institute of Radiological Sciences (NIRS), Japan; eleven (220)Rn monitors (four types) from nine laboratories were evaluated. The (220)Rn detection principle was the same for the eleven instruments and one reference instrument, which were commercially available silicon semiconductor detectors using an electrostatic collection method. The intercomparison results showed that there was a negative deviation of more than 30% in measured (220)Rn concentrations given by the laboratories relative to the reference values, which were obtained by making a decay-correction during the travel of (220)Rn through the sampling assembly (sample tube, filter and drying unit) and using a calibration factor.

Novel method for estimation of the indoor-to-outdoor airborne radioactivity ratio following the Fukushima Daiichi Nuclear Power Plant accident.

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan resulted in significant releases of fission products. While substantial data exist concerning outdoor air radioactivity following the accident, the resulting indoor radioactivity remains pure speculation without a proper method for estimating the ratio of the indoor to outdoor airborne radioactivity, termed the airborne sheltering factor (ASF). Lacking a meaningful value of the ASF, it is difficult to assess the inhalation doses to residents and evacuees even when outdoor radionuclide concentrations are available.

Variability of radiocaesium inventory in Fukushima soil cores from one site measured at different times.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the deposition of radioactive contamination of soils mainly by (134)Cs and (137)Cs. The contaminated areas are of a great concern since external radiation may lead to significant long-term doses to humans and animals. External dose rate above ground will decrease with physical decay of the radionuclides and as they migrate deeper into the soil with time.

Measurement of 90Sr in contaminated Fukushima soils using liquid scintillation counter.

A method based on liquid scintillation counting system has been developed for the measurement of (90)Sr in Fukushima soil samples due to contamination of (134)Cs and (137)Cs. Three soil samples were collected within 30 km radius from the Fukushima Daiichi Nuclear Power Plant (FDNPP). Activity concentration of (134)Cs and (137)Cs were measured using a gamma spectroscopy system with high-purity germanium detector.

Characteristics of indoor radon and its progeny in a Japanese dwelling while using air appliances.

Characteristics of radon and its progeny were investigated in different air conditions by turning four types of indoor air appliances on and off in a two-story concrete Japanese dwelling. The four appliances were air conditioner, air cleaner, gas heater and cooker hood. The measurements were done using two devices: (1) a Si-based semiconductor detector for continuous measurement of indoor radon concentration and (2) a ZnS(Ag) scintillation counting system for equilibrium-equivalent radon concentration.

Preliminary Experiments Using a Passive Detector for Measuring Indoor 220Rn Progeny Concentrations with an Aerosol Chamber.

This paper describes preliminary experiments using a passive detector for integrating measurements of indoor thoron (²²⁰Rn) progeny concentrations with an aerosol chamber. A solid state nuclear detector (CR-39) covered with a thin aluminum-vaporized polyethylene plate (Mylar film) was used to detect only alpha particles emitted from ²¹²Po due to ²²⁰Rn progeny deposited on the detector surfaces. The initial experiment showed that Mylar film with area density of more than 5 mg cm⁻² was suitable to cut off completely alpha particles of 7.

Estimation of external dose by car-borne survey in Kerala, India.

A car-borne survey was carried out in Kerala, India to estimate external dose. Measurements were made with a 3-in × 3-in NaI(Tl) scintillation spectrometer from September 23 to 27, 2013. The routes were selected from 12 Panchayats in Karunagappally Taluk which were classified into high level, mid-level and low level high background radiation (HBR) areas.

Development of an aerosol chamber for calibration of ²²⁰Rn progeny detectors.

This paper describes an aerosol chamber system that can be used for calibrations and performance experiments of passive (220)Rn progeny detectors. For the purpose of this study, an aerosol generation system using carnauba wax as the aerosol material was mounted into the (220)Rn chamber. We used the chamber to measure characteristics of the equilibrium factor (F) of (220)Rn and unattached fraction (f(p)) of (220)Rn progeny, which are important parameters for dose estimation.