A visual image of the scattered X-ray distributions gives us useful information for beginners to study radiation physics. A pin-hole camera for X-rays can be made by use of simple materials as well as a two-dimensional X-ray detector (imaging plate: IP). In contrast with a pin-hole camera for the visible radiations, a pin-hole camera for X-rays uses a collimator, having a sufficient thickness to reduce X-rays. This design causes the following problem: in the case in which the X-rays are incident to the collimator from the diagonal direction, the some X-rays are absorbed by the wall of the collimator. Namely, the images in the surrounding part of the IP are underrepresented. The aim of this study is to suggest a correction method of the underrepresentation. We used a pin-hole camera (320 mm(long)×270 mm(wide)×300 mm(depth)) by means of the clinically applied IP (10×12 inch). In order to determine proper conditions for a size of collimators (pin-hole), experiments using medical X-ray equipments were carried out. The efficiencies and resolutions were experimentally determined for the collimator sizes of 2 to 8 mm^φ. Then, images of scattered X-ray distributions were measured by the irradiation of a head phantom, and considerations were taken for a practical use of the pin-hole camera. Moreover, an exponential absorption of X-rays in the phantom was visualized by our camera in order to indicate a potential of quantitative analysis based on the image of scattered X-ray distributions.

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  Measurement and decontamination of surface of trees and surrounding wooden structures contaminated by radioactive substance were studied in the gardens and public parks of Northern Fukushima Prefecture which experienced radioactive contamination due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Plant. The counts per minute (CPM) above the centre surface of wooden garden tables in open air were 1.5 times higher than those of garden benches and 9 times higher than that of a garden bench in the square gazebo. Decontamination of wooden garden benches by high-pressure washing was more effective than planing. The counts per minute (CPM) above the soil around garden trees increased by 1.2 times after high-pressure washing. Radioactivity counting rate did not decrease when the leaves fallen from zelocova trees were removed; however, they decreased by about half when soil cover was installed at the base of the trees. Clearly, the upper surfaces of garden trees and wooden surrounding structures were strongly contaminated by radioactive substances, and they should be decontaminated by high-pressure washing before removing the surface soil.

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  The radioactive cesium concentrations have been measured for the soil samples in Bihoku area of the Chugoku region. The samples were obtained before and after 11 March 2011, when the accident began in the Tokyo Electric Power Co. Fukushima Daiichi Nuclear Power Plant. The Bihoku area is the mountain area around the center of the Chugoku region. For the measurements of the gamma rays, cesium atoms were isolated from the soils by using nitric acids. The ¹³⁴Cs activities were detected in the soils sampled at two locations in June 2011, where the soils were rich in leaf mold and rainwater smoothly flowed into the grounds. After correcting for the isolation rates, the ¹³⁴Cs concentrations were 1.86±0.24 Bq/kg and 0.70±0.22 Bq/kg, respectively. The former well agreed with that in the sample obtained in September 2011, and the latter also agreed with that in the sample obtained in March 2012. In a wood, a soil was sampled from a layer of 5 cm-10 cm in depth in September 2010. The ¹³⁷Cs concentration was 27.34±1.31 Bq/kg. In November 2011, the ¹³⁷Cs concentrations in two soil samples from the same layer were 35.79±1.68 Bq/kg and 37.43±1.98 Bq/kg. Three soil samples were obtained from two agricultural lands in January and March 2012. The ¹³⁷Cs concentrations in these samples were approximately 10 Bq/kg. No ¹³⁴Cs activity has been detected in the soil samples from the wood and the two agricultural lands.

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  Techniques to decontaminate stone and concrete surfaces by an easy and practical method were studied in Northern Fukushima Prefecture, which experienced radioactive contamination due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Plant. Radioactivity counting rate could be decreased to 1/5.5 by high-pressure washing with hydrochloric acid treatment with clothes after treating concrete surfaces twice with high-pressure washing. Radioactive contaminants could be disposed using high-pressure washing by collecting soil saturated with polluted water from crevices in concrete pavements. In addition, radioactivity counting rate decreased by overturning surfaces of small stones and concrete. In conclusion, hydrochloric acid treatment and covering could be used if the decontamination of concrete and stone surfaces by high-pressure washing and overturning was insufficient; however, the cost and dangers of using hydrochloric acid must be considered.

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  Radioactivity decontamination by replacing soil and soil cover with deep-level soil and soil cover in flower beds and a vacant place in Northern Fukushima Prefecture were studied, which experienced radioactive contamination due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Plant. Radioactivity counting rate 1 cm above the soil surface after replacing surface soil with uncontaminated deep-level soil decreased to 13.7% of the control in gardens. The concentration of radioactive cesium in the cover soil increased after 132 days; however, it decreased in the old surface soil under the cover soil in flower beds. A 10 cm deep-level soil cover placed by heavy machinery decreased the radiation dose rate to 70.8% of the control and radioactivity counting rate to 24.6% in the vacant place. Replacing the radioactively contaminated surface soil and soil cover with a deep-level soil was a reasonable decontamination method for the garden and vacant place because it is quick, cost effective and labour efficient.

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