Up till now, from a radiation safety management point of view, it has been discussed to construct guidelines on estimation of neutron fluxes produced via operating various medical small accelerators and to establish uniformly the clearance system related to having neutron activation effects into each accelerator facility.That is, it was the aim of this investigation to accumulate the data on estimation basis of neutron flux measurements at those medical small accelerators by an activation foil method.In this work, the neutron fluxes at the self-shielded PET cyclotron and the electron liniac apparatus of Tokushima University Hospital have been measured as the medical small accelerator.As a result, for the self-shielded PET cyclotron, it was found that the thermal neutron flux is (1.04±0.05) x107 cm^-2s^-1 and the fast neutron fluxes are distributed over the range 1x10⁴ (the neutron energy E_n=9MeV) to 1x10⁷ (E_n=1.5 MeV) cm^-2s^-1 into the radiation shelter, and while the thermal neutron fluxes would be distributed over the range 5.0x10¹ to 9.9x10¹ cm^-2s^-1 and then the fast neutron dose leakages were not detected outside there. For the 6/10 MV electron liniac apparatus, it was also found that nearly the same thermal neutron fluxes would be distributed all around the liniac room and those measured values are over the range (1.01±0.18) x103 to (1.32±0.10) x103cm-²s^-1.

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This work developed a fitting method of buildup factors for shielding calculation to predict the radiation dose of emergency actions in a nuclear power plant (NPP).The deviation for buildup factors of deep penetration calculated by the fitting were carefully estimated by varying the unit penetration depth, fitting range and method of inducing the error direction.Furthermore, as application examples of the optimum fitting parameters selected from the appearance frequency of penetration depth in NPP structures, the dose rates in movement routes during a nuclear disaster and also in recovery action in engineering safe guard system (ESFs) rooms was examined.The following results were obtained:(I) This method can extract the parameters with good accuracy for geometric progression formula (GP) using any fitting range.(2) The most suitable parameters for the evaluation object can be selected by changing the fitting conditions.(3) These GP parameters can be used to predict the radiation dose in the event of emergency action and to determine the priority level with recovery action of ESFs.

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Lumagel Plus scintillator was selected as the most suitable scintillator for simultaneous collection of H-3 and C-14 by using mono-ethanolamin (MEA) solution.The influence of air temperature and humidity on the collection efficien cy of H-3 and C-14 was examined.As the result, when the weight of water in MEA was less than 1000mg, the samples became colorless without separation into two phases, and the collection efficiency of 99% and more was obtained for C-14 within the collection time of 3.7 hours.On the other hand, the collection efficiency for H-3 decreased with increase of the weight of water in the collected air, but it was more than 90% even at high temperature of 30°C and high relative humidity of 90%.It was found that this method is practically useful for simultaneous determination of H-3 and C-14 concentration in air.

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A tabletop micro X-ray beam irradiation system has been developed to research biological radiation effects on living cells. The micro beam system is composed of a micro focus X-ray tube, a capillary for X-ray guide, an inverted microscope and others.A beam profile was measured by the knife-edge method and the focused beam size was proved to be 12μm in diameter. The micro dosimetric characteristics of the single cell irradiation was investigated by a photon-electron transport simulation.The maximum dose rate for a targeting cell was estimated to be 0.05Gy/s.
In a preliminary experiment, a normal human fibroblasts cell grown on a radiophotoluminescent glass plate was irradiated by the microbeam. After the irradiation, the targeting cell was stained with anti-γ-H2AX antibody to visualize the effects on DNA double strand breaks.In fluorescence microscopy, foci in the nucleus corresponding to the radiation damage and the X-ray beam spot were simultaneously observed at the position of the targeting cell.

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