To perform a safety assessment for the geological disposal of radioactive waste, it is important to understand the response characteristics of the disposal system. In this study, approximate analytical solutions for steady-state nuclide releases from the engineered barrier system (EBS) of a repository were derived for an orthogonal one-dimensional diffusion model. In these approximate analytical solutions, inventory depletion, decay during migration and the influence of groundwater flow in the excavation damaged zone (EDZ) were considered. These solutions were simplified by the Taylor theorem in order to clearly represent the response characteristics of the EBS. The validity of these solutions was shown by comparison with numerical solutions. The response characteristics of the EBS are useful for identifying target values for important parameters that would have the effect of improving the robustness of system safety. The robustness of the geological disposal system and the reliability of the safety assessment can thus potentially be improved using the approximate analytical solutions.

The effects of nitrogen doping as a terminator in an anodically oxidized film of tantalum have been investigated.

In the oxide film of nitrogen-free tantalum, the electric leakage current abruptly increased with the applied voltage. It is well-known as the Poole-Frenkel effect [1] [2]. After annealing at 623K in a hydrogen atmosphere, the leakage current increased.

On the other hand, in the oxidized films of nitrogen-doped tantalum the leakage current increased in proportion to the applied voltage, but it was very small as compared with the nitrogen-free oxide. Moreover the leakage current decreased after annealing. The decrement strongly depended on the amount of doped nitrogen.

We investigated the electrical and optical properties, the chemical composition, the surface morphology and the crystallinity of sputtered Sn-doped In2O3 films deposited on different substrate positions. Both the electric conductivity and the optical transparency are related to the free carrier density and moreover the preferred crystal orientation. The former relation is attributed to the Burstein-Moss effect and the latter suggests the Sn doping mechanism.

We have studied the distribution and diffusion of Te, Mg, and Zn dopants in GaAs which was grown by an LPE process. It was found that the distribution of the dopant atoms of Te and Zn in the Te-doped n-type epi-layer on the Zn-doped p-type substrate showed a sharp and clear interface. In contrast, the dopant distribution of Mg and Zn in the Mg-doped p-type epi-layer on the Zn-doped substrate indicated a diffuse interface because of significant interdiffusion. The X-ray diffraction of these epi-layers and substrates revealed that the Mg-doped epi-layer showed rather poorer crystalline quality than the other specimens. These experimental results can be accounted for by a model of charged vacancies in a p-type GaAs.

In order to realize a thin film of organic single crystals, we have been investigating fabrication process using vapour deposition technique. Up to now, highly oriented thin films of 2-methyl-4-nitroaniline(MNA) and 4-(N,N-dimethylamino)-3-acetamidonitrobenzene(DAN), both of which are promising organic materials for nonlinear optical devices, could be fabricated on a buffed polyimide and on a thermally oxidized silicon wafer, respectively. In the case of MNA films, a series of results by X-ray diffraction and by SEM observation showed weak two-dimensional characteristics suggesting the existence of topographic effects and/or of interaction between MNA molecules and molecular moieties of polyimide substrate. Small optical transmittance of both MNA and DAN thin films are explained in terms of light scattering by grain boundaries and surface roughness.