The diffusion of Ba in various carbons was investigated by electron microprobe ana-lyzer.
The analysis was carried out on an instantaneous source experiment. Diffusion coefficients were obtained by three methods: (1) slope of log C vs. X2, (2) total amount of diffusion sub-stances, and (3) coordinate of the point of inflexion in the concentration penetration curve. All methods gave values agreeing fairly well with each other. The diffusion coefficients and activation energies obtained were of the same order of the magnitude as the results obtained by other authors, and furthermore were in accord with the magnitude expected from the structure of impermeable carbons. The present method can therefore be considered as effective as out-pile tests for analyzing the diffusion mechanism of fission products.

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The neutron slowing down time in graphite was measured by means of capture γray detection. Bursts of fast neutrons produced by D-T reaction were injected into a graphite pile. Detection was by NaI(T1) scintillator covered by metallic foil of either In, Cd or Gd, serving as resonance absorber. The slowing down time was determined from the maximum point of the reaction rate registered by this counter and presented in the form of time spectrum. The values thus determined were 19.2±0.6, 39±3, 43.0±0.7, 46.1±1.0, 47.5±0.8, 55±2 and 85±6 μs, for 1.58, 0.48, 0.44, 0.40, 0.36, 0.30 and 0.17 eV respectively. These values agree well with calcu-lated based on crystal model. The time response of the resonance detector also was in reasonable agreement with calculation. The effect of the medium being finite and that of detector position on the observed slowing down time were estimated. From this experiment, it became clear that the process of the neutron slowing down shows some definite influence of the crystal effect of graphite and is explained pretty well by Williams' model.

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With the aim of finding the most desirable set of conditions for powder metallurgical preparation of graphite matrix fuels containing thorium carbide, the properties and structure of fuel samples prepared by compacting various mixtures of powdered material followed by heat-ing were investigated.
It was found that of the resulting compacts those consisting of (1) purified and milled na-tural graphite powder, (2) metallic thorium powder and (3) furfuryl alcohol as binder showed the best properties after heating to 600°C. These compacts possessed 1.902.40 g/cc density, kg/mm² Vickers hardness, a thermal expansion coefficient at 900°C of about 14×10^-6/ °C in the direction parallel to, and 2.5×10^-6/°C normal to pressing direction, and a thermal conductivity, in the same temperature range, of 0.02 (parallel) and 0.07 cal/cm•sec°C (normal).
Since these favorable properties and structural features are not impaired by heating to about 2, 000°C subsequent to treatment at 600°C, it can be said that a new, simple and effective set of conditions for fuel preparation has been found.

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The thermal diffusivity of the ThO2-UO2 system in solid solution was measured by laser pulse method at temperatures ranging from 20° to 500°C. Reproducibility of the data was confirmed to be within 3%. The compositions of the samples were ThO₂, ThO₂-1%UO₂, ThO₂-5%UO₂ and ThO₂-10%UO₂.
The thermal conductivity was calculated from measured thermal diffusivity data and the specific heat data available in literature and corrected to zero porosity by using Loeb's equation, in which the shape factor is unity.
The values on ThO₂ thus obtained agreed very well with the data found in literature, throughout the range of temperature of the experiments. The thermal conductivity of ThO₂, ThO₂-1%UO₂, ThO₂-5%UO₂ and ThO₂-10%UO₂, at 20°C, were 0.0312, 0.0288, 0.247 and 0.0184 cal•cm/sec•°C.cm², respectively.

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Thermoluminescence and electron paramagnetic resonance (EPR) of CaSO₄(Mn) powder have been studied. The intensities of the hyperfine lines in the EPR spectra of Mn⁺⁺ and the heights of the thermoluminescence glow peak are found to change in parallel, upon varying the conditions of heat treatment and the concentration of Mn⁺⁺ It is also found that Mn⁺⁺ present in aggregate state, which gives a broad EPR spectrum, is not an effective activator for ther-moluminescence; heat treatment at high temperatures serves to disperse this aggregated Mn⁺⁺, which increases the thermoluminescence sensitivity. The relation between the thermolumines-cence intensity and the radiation dose is linear, so long as the duration of irradiation is within certain limits; the deviation from the linear relation is explained in terms of fading of ther-moluminescence at the temperature of irradiation.

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The oxidation behavior of uranium monosulfide powder in oxygen and air has been studied over a range from room temperature to 900°C, by means of DTA, TGA, X-ray diffraction and chemical analysis. Most of the reactions occurring during the oxidation process have been identified. Intermediate oxidation products observed are γ-US₂, UOS, UO₂SO₄, UO₂ and UO_2+x.

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The radial distribution of photons backscattered in the direction perpendicular to the front face of a semi-infinite scatterer was examined for the case of a point isotropic γ-source placed on the scatterer. As a result, the following relations were found:
where N_n(r) and I_n(r) respectively are the fractions of photons and energies emerging perpen-dicularly at a point r.
Monte Carlo calculations by collision density method was performed to confirm the validity of the above relations, as well as to verify that the radial distribution of photons backscattered in all directions from the slab surface is subject to the same relations as above.
The values of the constants an and bn obtained by experiment were rather smaller than those by calculation, but the values of the constants for the radial distribution of photons backscattered in all directions were nearly equal to those for the normal direction. The rela-tion between the values of the constants and the number and energy albedos was examined.

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