Radiation Safety Management
Online ISSN : 1884-9520
Print ISSN : 1347-1511
ISSN-L : 1347-1511
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Displaying 1-3 of 3 articles from this issue
  • Wiseman Chisale BEKELESI, Triyono BASUKI, Satoru NAKASHIMA
    2022 Volume 21 Pages 1-12
    Published: 2022
    Released on J-STAGE: May 13, 2022

     The long-term migration of 137Cs in the environment is mainly through the 137Cs adsorbed on the dispersed soil particles of various sizes. However, the transfer of 137Cs from soil to plant, especially rice plant, remains questionable. The objective of this study is to determine the relation among soil characteristics, 137Cs distribution and transfer factor (TF) of 137Cs from soil to rice. In this study paddy fields in Kawauchi and Fukushima were chosen. This is because more studies have focused only on one sampling field and there have not been much discussion comparing various fields as envisaged in this study. The results have shown that TF for Kawauchi is 5-fold higher than that of Fukushima. Physicochemical properties of the soils showed that Fukushima soil has less percentage of exchangeable 137Cs and high percentage of exchangeable K in contrast to Kawauchi soil. These factors likely disturbed the transfer of 137Cs from soil into the rice plant. Powder X-ray diffraction has shown that Fukushima soil is rich in micaceous minerals which also release a lot of K+ to distract the 137Cs transfer. This study suggests that the presence of micaceous minerals in the soil would be a good amendment for radiocesium-contaminated rice paddy fields in enhancing adsorption of 137Cs in the soil. However, there is still a need to investigate adsorption kinetics of 137Cs to ascertain higher values of TF in Kawauchi soil.

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  • Hiroshi MATSUMURA, Go YOSHIDA, Akihiro TOYODA, Kazuyoshi MASUMOTO, Haj ...
    2022 Volume 21 Pages 13-25
    Published: 2022
    Released on J-STAGE: July 02, 2022

     It is essential to clarify the characteristics of the material activation in cyclotron-type proton therapy facilities for future decommissioning. In particular, concrete occupies the largest volume among object materials, but its activation characteristics of activity level and distribution are unknown. We investigated concrete radioactivation in cyclotron-type proton therapy facilities at the National Cancer Center Hospital East and Aizawa Hospital. The in situ 24Na measurement method, which is easy and high sensitivity, was applied for the investigation. Using the in situ 24Na measurement method, we obtained the thermal neutron fluence rates in concrete with high sensitivity. Based on these fluence rates, the sum of the 152Eu and 60Co specific activities in the concrete were predicted for an operation duration of 30 years. The study aims to predict general 152Eu and 60Co (which are major radionuclides) specific activities for cyclotron-type proton therapy facilities, and we found the following common characteristics in the investigation results. In the accelerator room, neutrons were mainly produced at the degrader and/or objects surrounding it and diffused over the room. As a result, the sum of the ratios of the concrete floor's specific activities of 152Eu and 60Co for their respective clearance level (0.1 Bq/g) was estimated to be close to 1. On the other hand, the production of neutrons both in the treatment and beam transport line rooms was low, and the sum of the ratios of the 152Eu and 60Co specific activities for their respective clearance level was estimated to be below 1.

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  • Wiseman Chisale BEKELESI, Triyono BASUKI, Shogo HIGAKI, Satoru NAKASHI ...
    2022 Volume 21 Pages 26-35
    Published: 2022
    Released on J-STAGE: October 26, 2022

    Strontium-90 (90Sr) and cesium-137 (137Cs) were released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Strontium-90 concentration in environment was extremely lower than that of 137Cs in the soil after the FDNPP accident. However, 90Sr may induce higher risk of health effect to human than 137Cs by considering longer biological half-life of 90Sr than 137Cs. Moreover, there is not sufficient data on 90Sr horizontal and vertical distribution compared to 137Cs, which is important for predicting their long-term migration. In the present study, the distribution of 90Sr and 137Cs in the soils of Kawauchi and Fukushima paddy rice fields was investigated and the migration of 90Sr and 137Cs in Lake Ogi sediment and its forestry catchment area was studied. A rough relation between 90Sr and 137Cs levels in soil is shown and such insufficient correlation might be defined by the low 90Sr concentration and because of global fallout. Furthermore, 90Sr gave higher coefficient of variation in comparison to 137Cs, portraying that the movement of 90Sr is more affected by the environmental factors rather than 137Cs. The depth dependency of 90Sr and 137Cs in Lake Ogi forestry catchment area is shown for both radionuclides, and the activity concentration decreases with the increase of depth. However, the 90Sr infiltrates more to 10 cm soil profile in contrast to 137Cs, showing 90Sr faster vertical migration than 137Cs. Sediment to soil ratio for 90Sr reported a higher value than that of 137Cs, which possibly depicts more horizontal flowing of 90Sr from forest soil to lake sediment than 137Cs. Consequently, the higher mobility of 90Sr than 137Cs was proposed.

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