A study was made of the correlation between the focusing of an ion beam and thespatial distribution of the ion density in the source plasma, which determines thegeometrical shape of the plasma boundary, using a duoplasmatron ion source. It wasrevealed that the focusing of the ion beams extracted from a gaseous plasma through alarge-area single aperture is sensitively influenced by the concavity of the plasmaboundary, which concavity varies with the radial density profile of the plasma ions atthe plasma boundary.

View full abstract

A method of calculation is described to estimate the average number of neutronsemitted per fragment in medium-excitation fission from published experimental data onneutron emission in thermal-neutron induced fission, average total kinetic energy as afunction of fragment mass and mass yield in low- and medium-excitation fission reactions.Use is made of a relation of fragment excitation energy with internal excitation anddeformation energies, and the difference in kinetic energy between the fission reactionsat two-excitation energies. A tentative calculation is made for the fission of ²³⁸U inducedby 12 MeV protons. The results are in good agreement with experimental data.
The method developed in the present work may make it possible to predict theaverage number of neutrons emitted from individual fragment in medium-excitation fis-sion which has not yet been measured experimentally.

View full abstract

The parameter identification and adaptive control schemes applied in a previous study to a nonlinear point reactor are extended to the case of a loosely-coupled-core reactor with internal feedbacks, constituting a nonlinear overall system. Both schemes are shown to be stable, with the system newly represented on the pattern of the Model Reference Adaptive System (MRAS) with use made of the Lyapunov's method.
For either parameter identification or adaptive control of a loosely-coupled-core reac-tor, there exists no canonical form of multiple input-multiple output system which can be directly applied for deriving the MRAS with the matrix version of the Kalman-Yakubovich lemma as it was in the case of the point reactor. This difficulty is circum-vented by the practical assumption that the neutron density can be directly measured on each core as reactivity change is applied as input into the coupled core as a whole. For parameter identification, the model parameters are adaptively adjusted to those of each core, while for the adaptive control, plant parameters of each core can be adaptively compensated, again through control inputs, to asymptotically reduce the output error between the model and the plant.
The point reactor is shown to correspond to a special case.

View full abstract

In the subcooled decompression experiments of water in a vertical tube under a tem-perature gradient, a violent pressure oscillation was observed. By varying the gradient conditions it was ascertained that this pressure oscillation was due to the existence of the large temperature gradient in the system, and that it occurred in the low tempera-ture region of the system. The generation of the pressure oscillation could be explained by assuming a reflection surface for the pressure wave caused by the blowdown. Two positions of the reflection surface were experimentally obtained from the structure of oscillatory pressure behavior and by computing the autocorrelation function of the pres-sure curve. In the system of a linearly descending temperature distribution, a flashing occurred partially and those two values were in good agreement with the position of the phase boundary generated just after the passage of the decompression wave.
The conventional thermal equilibrium model could not completely explain this oscilla-tion. The anomalous pressure peaks appeared in the calculated pressure curve resulting from the prompt flashing in the second supersaturated region. Photographic observation showed that this region was kept in the supersaturated liquid state during the oscillation and that a flashing was delayed. 'Introduction of the flashing delay time into the thermal equilibrium calculation has well succeeded to reproduce the oscillatory pressure behavior.

View full abstract

The influence of γ-irradiation on the bulk etching rate of cellulose nitrate is described. The increase in bulk etching rate induced by r-ray from ⁶⁰Co has been measured at different irradiation doses and at different etching temperatures. From this temperature dependence the activation energy for the etching reaction is obtained. Some conclusions derived from experimental results are discussed in relation to a criterion for track registration.

View full abstract

The behavior of hydrogen in liquid sodium containing relatively large amounts of oxygen were investigated with the aid of the hydrogen sensor of niobium membrane. The partial pressure of the hydrogen in liquid sodium at hot zone of a cold-trapped na-tural circulation sodium loop was measured as functions of temperatures of the cold trap and the hot zone of the loop. It was observed that at constant cold trap temperature the partial pressure of hydrogen in sodium increases with increasing the hot zone tem-perature. This study also showed that, keeping the temperature of hot zone constant, a logarithmic plot of hydrogen concentration calculated from the equilibrium hydrogen partial pressure vs. the reciprocal temperature of cold trap yields a straight line whose slope is nearly equal to that on the solubility of sodium hydroxide in sodium. Finally, it was observed that the permeation of hydrogen in sodium through a niobium membrane is a process controlled by diffusion. But the permeability for hydrogen in niobium is a few-hundredths smaller than that in literature, owing to the oxide film on the membrane surface.

View full abstract

A solid uranium amalgam containing as high as 1.7 g U/ml Hg was prepared electro-lytically using a two-compartment electrolyzer separated with a cation exchange mem-brane at a kilogram scale. The design and operation characteristics of the electrolyzer is described. The results indicate that ca. 170 g of uranium ion in an aqueous solution could be reduced to metallic state by forming amalgam within 4 h with a current efficiency of 30% and uranium recovery of more than 80%

View full abstract

An examination is made of the dependence shown by the nuclear characteristics of a D-D fusion reactor blanket cooled by particles of boron carbide (B₄C) suspended in gas, on the design variations such as ¹⁰B enrichment in B₄C and the B₄C concentration in the coolant channel.
The results of calculation reveal that the flow of B₄C particles containing ¹⁰B with the natural abundance and loaded to the maximum attainable concentration is an optimal choice as coolant in terms of nuclear characteristics: the blanket cooled by the flow exhibits the maximum nuclear heating, the minimum neutron energy leakage and the minimum induced activity. The flow also would have the advantage of the lowest cost on account of no need of additional processing to enrich or deplete ¹⁰B.

View full abstract

This report is dealing with the basic mechanism for fast neutron dosimeter. It was based on the principle that the protons produced by elastic scattering between fast neu-trons and hydrogen atoms in polyethylene powder will excite their neighbor thermo-luminescent material CaSO₄: Tm powder. The mathematical formulation was according to Takenaga's approach. The optimum mixing weight ratio of polyethylene to CaSO₄: Tm was found to be 2:1. In this study the total experimental error for fast neutron dose determination was about 12%.

View full abstract