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The beam shaping assembly design has been investigated in order to improve the epithermal neutron beam for accelerator-based boron neutron capture therapy in intensity and quality, and dosimetric evaluation for the beams has been performed using both mathematical and voxel head phantoms with MCNP runs. The neutron source was assumed to be produced from a conventional 2.5 MeV proton accelerator with a thick (7)Li target. The results indicate that it is possible to enhance epithermal neutron flux remarkably as well as to embody a good spectrum shaping to epithermal neutrons only with the proper combination of moderator and reflector. It is also found that a larger number of thermal neutrons can reach deeply into the brain and, therefore, can reduce considerably the treatment time for brain tumours. Consequently, the epithermal neutron beams designed in this study can treat more effectively deep-seated brain tumours.

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The practical feasibility of 126 Sn transmutation in spallation targets of accelerator-driven systems was evaluated from the viewpoints of accumulation of radioactive spallation products and neutron production as well as transmutation amount of 126 Sn. A cylindrical liquid 126 Sn target whose length depends on proton beam energy was described, based on a Pb-Bi target design of accelerator-driven system being developed in JAEA. A proton beam of 1.5 GeV-20 mA was estimated to give the transmutation rate of 126 Sn 6.4 kg/ yr, which corresponds to the amount of 126 Sn annually discharged in 27 LWRs of 1 GWt and 33 GWd/ THM. The equilibrium radioactivity of spallation products would reach 9% of that of 126 Sn transmuted in the spallation target, and the equilibrium toxicity would be just 3%. Some parametric analyses showed that the effective half-life of 126 Sn could be reduced through a proper reduction of the target size. The 126 Sn target was calculated to produce 40 neutrons per proton of 1.5 GeV and give a neutron spectrum very similar to that of the reference Pb-Bi target. As a result, the transmutation of 126 Sn in the spallation target has a high feasibility in terms of better transmutation performance and comparable target performance.

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We report on optical reflection measurements on ternary alloy (CdMg)Te thin films grown by molecular beam epitaxy. Data have been obtained in the spectral range between 1.2 eV and 2.8 eV, and at temperatures between 300 K and 77 K.The reflection coefficient as a function of energy E has been theoretically described taking into account multiple reflections at the interfaces involved. The dispersion relation $(€) = a + bP/[1 -(€/c)~] has been used. A comparison with the experimental data has yielded the refractive index as a function of energy. The value of the refractive index n is given as a function of energy for the ternary alloy (CdMg)Te for different Mg concentrations and different temperatures. These results are essential for designing efficient waveguides for semiconductor laser structures using (CdMg)Te as a base material.

The impacts of chemical stability of inert-matrix-fuel (IMF) on the material attractiveness for states and non-state actors were evaluated in an open transuranic fuel cycle employing high temperature gas cooled reactors. The methodology for material attractiveness evaluation was developed to assess material attractiveness for states and treat IMF which is chemically inert for nitric acid solution. The material attractiveness was relatively assessed with physical properties of material in each of three discrete phases in the development of a nuclear explosive device. The material attractiveness assessment for non-state actors revealed that the non-irradiated TRISO fuel particle and IMF kernel for high temperature gas cooled reactors and the non-irradiated mixed oxide fuel (MOX) powder for MOX light water reactors were the most vulnerable targets in each fuel cycles. The TRISO fuel particle and IMF kernel would have less material attractiveness than the MOX powder because of their greater processing time and complexity. The material attractiveness assessment for states aiming concealed diversion revealed that the TRISO fuel particle and IMF kernel have less material attractiveness than the MOX powder, and are regarded as irradiated uranium fuel grade in the material attractiveness.