An important application of neutron beam is boron neutron capture therapy(BNCT). Many facilities have recently been planning to use an accelerator for BNCT, in which cancer cells as well as normal cells near a cancerous region may be exposed to neutron beams with different energy profiles. In the present study, the cell killing effect and induction of DNA double-strand breaks(DNA-dsb) by neutron beams of different energy profiles were studied in Chinese hamster ovary(CHO-K1) cells and their radiosensitive mutant(xrs-5) cells. A neutron beam with mean energy 2MeV generated by the Neutron Exposure Accelerator System for Biological Effect Experiments(NASBEE) was more effective for cell killing than the thermal to epithermal neutron beams generated by the Heavy Water Facility of the Kyoto University Research Reactor(KUR-HWF). A focus assay of the repair protein of 53BP1 revealed a significant induction of DNA-dsb by these two neutron beams, but no significant difference in the induction and repair capabilities was noted between the two. These data suggest that an increase in the mean energy of neutron beam from thermal to fast neutrons increases cell killing effects, but not the induction of DNA-dsb.
We investigated the relationship between radiocaesium(134Cs and 137Cs) concentration(specific radio activity:Bq/kg) in rice and the paddy soil in Iitate village where people evacuated because of the high levels of radioactive contamination caused by the Fukushima Daiichi nuclear disaster. The radiocaesium concentration was measured of paddy soil and of lowland rice grown on variously decontaminated paddy soil in the year 2012 and 2013. The results showed that the concentration of radiocaesium in the brown rice cultured in the field of Sasu and Maeda with 2000 - 6000Bq/kg(DW) soil(0 - 15cm depth) was below 40Bq/kg, which was below the new standard for food(100Bq/kg), and the concentration of radiocaesium in the brown rice depended on the decontamination level of the paddy soil. In addition, the radiocaesium in rice was reduced depending on the exchangeable K content of the soil, which comes to plateau around 20mg K2O/100g dry soil. However, in 2013, in the fields of Komiya where the radiocaesium concentration was higher than 8000Bq/kg(DW) even after decontamination, brown rice with higher than 100Bq/kg was harvested, indicating the necessity of further decontamination. Overall, our results show that the suitable decontamination and additional fertilization of K can make the radiocaesium concentration of rice much lower than the new standard.
Much radioactive material was released to the environment with a Tokyo Electric Fukushima Dai-ichi Nuclear Power Plant accident. The quantity of the existing radioactive caesium is determined by evaluating total absorption peak on an energy spectrum observed by using a semiconductor detector. The conventional methods including this method have detection efficiency in inverse proportion to square for the distance of the radioactive material and the detector. If there is contamination with radioactive species in the neighborhood, a correct evaluation becomes difficult. It is necessary to put a sample and the detector in a heavy lead container. We suggest the simple and easy measurement method for 134Cs emitting plural γ rays. In the case of 134Cs, the release ratio of the γ rays of 605keV and 796keV is high. It is possible to have the detection efficiency in inverse proportion to the fourth power of the distance by the coincidence measurement of these γ rays. It means that the measurement by this technique is less affected by neighboring contamination. The determination of radioactivity is performed only by counting to occur on the coincidence measurement by use of NaI(Tl) scintillation detectors and the peak analysis on the spectrum is not necessary. This technique does not need a shielding container. Hence, it is possible to determine the radioactivity by in situ and non-destructive measurement in the environment.
A survey of personal dose equivalent for children using optically stimulated luminescent dosemeters has been carried out in the southern Miyagi Prefecture from 1 September 2011, about a half year after the Fukushima Daiichi Nuclear Power Plant accident. The survey results until November 2013 are summarized in this paper. This is the only survey report in Miyagi Prefecture as any survey of personal dose equivalent was not carried out in this area. Findings of indoor and outdoor staying time(home and school) for children were also reported. It was found that the most time(14 - 15 hours a day) was spent at the inside of their houses for all ages. Children stay at the inside of their houses and school about 21 hours a day in a total. These results are quite important to explain individual dose for children and to take measures to reduce exposure dose as well.
Radiological impact of releases of radionuclides into the environment should be evaluated with the aid of mathematical models with proper radionuclide transfer parameters in the environment needed to be assessed. However, this is not always practicable, and thus there is reliance on data obtained from the literature. For many years the IAEA has been very active to collect and evaluate data on radionuclide transfer through food chain in the environment to humans. They published collections relevant to the transfer in the environment, which is regarded as international reference values. The present paper describes radionuclide transfer parameters, with special emphasis on three transfer parameters, transfer factor from soil to plant, transfer parameters from feed to animal products, and concentration factor from water to aquatic biota. Main part of the information comes from the publication of the IAEA. For each of these parameters, definition of the parameter, geometric average and maximum and minimum of reported parameter values, and the modifying factors to parameter values are elaborated. The TEPCO Fukushima Dai-ichi Nuclear Power Plant Disaster resulted in a local environmental contamination of radionuclide. It is needed that information relevant to radionuclide transfer in our environment should be abstracted from the environment as much as possible.
The energy transfer between neutron and materials can occur in the scattering process with slow neutron because it possesses an incident energy, which is comparable to thermal energy of materials. That is to say, we can investigate inelastic and quasielastic neutron scattering from materials with slow neutron. There exist various dynamics in a very wide temporal and spatial scale as well as hierarchical structure due to motional degree of freedom for soft matter including polymers. However, the dynamical measurements with neutron has not been actively performed compared to the structural analysis by small angle neutron scattering. It is considered that we have to investigate both structure and dynamics of soft materials in order to understand it's functionality and physical properties adequately. In this review, we mainly focused on the dynamics of polymer in solid sate covering four topics：(i) low energy excitation in far below glass transition temperature(Tg)；(ii) evaluation of crystalline elastic modulus by phonon dispersion curve；(iii) local relaxation process “fast process”；(iv) the relationship between gas permeability and local dynamics.