An exact equation, for use in the calculation of the γ-ray streaming after single scatterings in a cylindrical duct, and its approximate formula, are presented. The dose of single scatterings at the exit of a cylindrical duct from a disk source at the entrance can be approximated by
D={4π/(n+1)}S_ak₁E₀Q(L/R₀)^-2 for s0 ?? L/R₀ ?? s1
={4π/(n+1)}S_ak₂E₀Q(L/R₀)^-3 for s1 <L/R₀ ?? 60,
where D = dose at the exit of the duct, S_a = source strength, n = a parameter of the angular distribution of the source, E₀ = energy of the source photons, Q = conversion factor, R₀ = duct radius and L= duct length.
The coefficients k₁ and k₂, as well as the constants s₀ and s₁ vary with source energy and wall materials. The values for lead, iron, concrete, tin, magnetite concrete, graphite and water are given in graphical representation for an energy range from 0.5 to 10 MeV.
A study is made of the distribution of the arrival probabilities of photons, corresponding to the positions of scattering points for the photons from the source to the duct exit. It was found that the effective scatterings contributing to the flux at the exit occur mainly in the shallow part of the duct wall, near its surface.

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Temperature coefficients of slightly enriched UO₂-H₂O lattices were measured in the Ozenji Critical Facility and analyzed in terms of critical parameters. The lattices studied were mainly those of 2.5% enriched UO₂, 10 mm in diameter and clad in 0.8 mm thick Al tube, and with water to fuel volume ratios of 2.5 and 1.5. Analyses were made with Deutsch's four factor critical equation and also with three group one dimensional diffusion calculations.
The result shows the importance of the influence of the reflector, which is the largest positive contribution to the temperature coefficient, being about 1×10^-4Δk/k/°C. This was experimentally demonstrated by measuring the coefficient for a core with an inner reflector water gap. Analyses also show that the discrepancy between experiment and calculation, which increases from 0.2 to 0.7× 10^-4Δk/k/°C as the water to fuel volume ratio decreases, may be mostly resolved by applying correc-tions for the space-dependent spectrum within the cell using the THERMOS code and for the effect of Dancoff factor with the TUZ-ZUT code. Calculation with these corrections applied reproduces experiment within an accuracy of about 0.2×10^-4Δk/k/°C over the temperature range of 20°to 70°C.

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Fast reactors having a 3, 000 l core volume fueled with ceramic Pu-U and Pu-Th are compared with each other for their reactivity effects due to large-scale loss of coolant. Using one-dimensional multi-group calculation, the maximum volume fractions of fuel for both fast systems are determined on the assumption that total loss of sodium in the core should not result in positive reactivity effect. It is concluded that Pu-Th fast reactors can be charged with more than several volume percent of fuel above the limit applicable to Pu-U fast reactors.

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A simple correction formula is analytically derived to reduce the error due to coarse mesh adjacent to absorbing regions in diffusion code calculations. The formula is derived by equating the neutron current, obtained by the three point difference equation with a finite mesh size, with the true value corresponding to zero mesh size. The formula is numerically confirmed to be quite satisfactory in practical two dimensional critical calculations with quite coarse mesh size.
When a transitional fine mesh region is adopted to represent the geometrical heterogeneity in the vicinity of the absorber region, the error is almost entirely determined by the mesh size in the transitional region and the correction is only necessary for the mesh size therein if the region thickness is above one and a half times the diffusion length.

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A generalized theory of the Rossi-α method is shown and is applied to the analysis of an experiment made with a remotely subcritical system.
Starting from the neutron transport equation, a general expression for the probability of detecting correlated neutrons is given, which is a function of the positions and sensitivities of the neutron detectors used in the experiment.
Some numerical examples for this expression are also given under the one-group diffusion approximation for comparison with the experiment. The agreement between them is satisfactory.

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The cross-sections for excitation of π electrons in para-polyphenyls by electron impact are calculated by means of the Born approximation, using the free electron model and Davydov's exciton theory.
Our results indicate that the relative radiation stability of para-polyphenyls tends toward a certain value as the number of benzene rings involved in para-polyphenyl increases. Qualitative agreement with experiment is obtained in a satisfactory manner.

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Tensile tests were made on wires of Magnox AL80, Mg-Al alloy and unalloyed magnesium at room and liquid nitrogen temperatures. The grain size dependence of the yield and ultimate tensile stresses were investigated.
It was found that the Petch relationship, σ_y=σ₀+k_d^-1/2, was satisfied even for specimens as slender as 1 or 2 mm diameter, though definite values of σ₀ and k were not obtained. It is thought that the preferred orientation in the wire has an influence on both σ0 and k. Similar results were also obtained for ultimate tensile stress.
The strain rate dependence of the yield and ultimate tensile stresses were also investigated.

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