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.

 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.

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.