Nobuyuki Sugiura

Measurements of summer radon and its progeny concentrations along with environmental gamma dose rates in Taiwan

The concentrations of 222Rn (radon) and its progeny with surrounding environmental gamma-dose rates were measured simultaneously inside and outside of buildings at 10 locations around Taipei and Hualien in Taiwan. For summer radon in Taiwan, indoor concentrations were estimated to be about 20 Bq m(-3) with about 90 nSv h- of environmental gamma, and outdoors, about 10 Bq m(-3) with about 70 nSv h(-1). The equilibrium factors were calculated to be 0.2-0.3 indoors and 0.3-0.4 outdoors. Indoor radon concentration had a weak positive correlation with gamma-dose rate. Since there is a possibility that high radon concentrations exist indoors during the cool season in Taiwan because of extremely low ventilation rates in the dwellings, a winter survey in January through February will be needed for future estimation of the annual effective dose.

Methodology using a portable X-ray fluorescence device for on-site and rapid evaluation of heavy-atom contamination in wounds: a model study for application to plutonium contamination.

Workers decommissioning the Fukushima-Daiichi nuclear power plant damaged from the Great East Japan Earthquake and resulting tsunami are at risk of injury with possible contamination from radioactive heavy atoms including actinides, such as plutonium. We propose a new methodology for on-site and rapid evaluation of heavy-atom contamination in wounds using a portable X-ray fluorescence (XRF) device. In the present study, stable lead was used as the model contaminant substitute for radioactive heavy atoms. First, the wound model was developed by placing a liquid blood phantom on an epoxy resin wound phantom contaminated with lead. Next, the correlation between the concentration of contaminant and the XRF peak intensity was formulated considering the thickness of blood exiting the wound. Methods to determine the minimum detection limit (MDL) of contaminants at any maximal equivalent dose to the wound by XRF measurement were also established. For example, in this system, at a maximal equivalent dose of 16.5 mSv to the wound and blood thickness of 0.5 mm, the MDL value for lead was 1.2 ppm (3.1 nmol). The radioactivity of 239Pu corresponding to 3.1 nmol is 1.7 kBq, which is lower than the radioactivity of 239Pu contaminating puncture wounds in previous severe accidents. In conclusion, the established methodology could be beneficial for future development of a method to evaluate plutonium contamination in wounds. Highlights: Methodology for evaluation of heavy-atom contamination in a wound was established. A portable X-ray fluorescence device enables on-site, rapid and direct evaluation. This method is expected to be used for evaluation of plutonium contamination in wounds.

Neutron Leakage From Polyethylene Slit

A measurement of neutron dose rate on iron-polyethylene shielding structure was carried out by 252Cf source. Simulated geometry was slit-like opening of polyethylene in iron slab and polyethylene slab shielding. These experiment was done at research facility of Hazama Co,. Iron slab and polyethylene slab thickness were 10 cm each. A gap of the polyethylene was simulated. Neutron REM-counter, polyethylene covered BF3 counter (STUDSVIK 2202-D), was used for measurement of streaming neutron dose equivalent. The solid state track detector (SSTD), allyl-diglycol-carbonate, were used for measurement of fast neutron dose equivalent in the range of 170Kev to 15Mev. The experimental data was obtained against gap width, source location and detector location. Obtained data shows strong correlation between dose rate and above parameters. These data was investigated in the view of to make use of actual facility design and compared with calculation such as MCNP4B. From the result of gap streaming experiment and calculation, we obtained allowable gap width as 6mm for this case (10cm polyethylene thickness).

Development of a method for estimating the airborne concentration of radon progeny, using an imaging plate

Publisher Summary The airborne 222 Rn (radon) progeny is a primary natural radioactive source generating an effective dose. It is important to identify high concentration areas for the radon progeny and to estimate these concentrations in air. However, most of general commercial instruments for measuring radon progeny concentrations using a precise electric detector are not perfect, because they are not suitable for use in high humidity environments that can reach up to 100% such as caves, utility mains, spas, and underground facilities. A new technique for estimating the airborne concentration of individual radon progeny has been developed. This method uses an imaging plate (IP) of BAS-III as a radiation detector. This system has a strong advantage due to the special IP feature for measurements in environments with extremely high humidity. In addition, the mobility to sample the environmental data is high because of the simple construction and light weight of the IP and cassette. An electric device is not needed to record the alpha information from the sample filter into the IP.

Neutron Streaming Experiment for Radiation Shielding Hatch by 252Cf Source

aNuclear facilities with strong radioactivity need massive concrete shields. In the view of shielding design, there arise some difficulties in the estimation of radiation doses from a gap or a void between the hatch and the wall. So, there is a need of experimental data and calculational procedures on such geometry for a reasonable shielding design. The experiments were carried out by 252Cf neutron source. A gap between the shielding hatch and the wall, and the offset of the shielding hatch were simulated by piling up the concrete slabs to the height of 30 cm. The thickness of the slabs are 10 cm each. Neutron dose was measured by REM-counter and CR-39 plate. To simulate various types of the shielding hatch, gap width and offset length of each gap were changed. Results of the experiments shows that the dose rate goes up with increment of gap width when the offset was fixed. The experimental data were also compared with the calculations by MCNP4B. We obtain the guide of design for radiation shielding hatch.

Analysis of Neutron Streaming Experiment for Torus Duct by Cf-252 Neutron Source

The neutron streaming for torus duct was investigated experimentally and analytically by using actual scale of experimental setups and 252Cf neutron source, in order to obtain the basic data of the shielding design such as the nuclear fuel facilities. The torus ducts with 1 m of radius of curvature and 3 cm and 5 cm of the duct diameters were used. Neutron doses were measured by REM counter and solid state track detector (SSTD). The MCNP4A calculation was done for the comparison with the experimental results. In the case where the arrangement of the source and the detector is comparatively able to foresee through the duct, the doses were high as a matter of course. In the case where the other side could not be foreseen directly through the torus duct, the dose became 4E-2 as compared with the straight duct. The dose for 3 cm of the duct diameter was generally smaller than that of 5 cm. The doses for 3 cm increased only 7% as compared with the bulk case (90 cm thickness, source position: disk, detector position: center).

On-line Measurement of Oil Void Fraction by Using a Small Neutron Source

配管中の油中気泡割合を測定する方法として, 小型の中性子源と減速材型中性子検出器の組合せによるオンライン型ボイド率測定法を開発した。線源には高速中性子源である252Cfを使用し, 測定時のバックグラウンドを低減するために, 減速材厚みや測定部周囲の遮蔽等を検討した。静止状態でボイド率の校正を行い, さらにシャシーダイナモ上で実車によるAT油中のボイド率を実測し, 重量測定法との比較により本測定法の有効性を検証した。