Ammonium plutonium(IV) fluorides, PuF₄•7/6NH₄F and PuF₄•2NH₄F, were prepared by the addition of an acidic solution containing Pu(IV) to a mixed solution of NH₄F and HF. Anhydrous PuF₃ was obtained by thermal decomposition of the ammonium plutonium(IV) fluorides under reduced pressure or else in an inert gas flow. The anhydrous fluoride was then reduced with Li vapor to Pu metal. Cerium metal was prepared by the same method.

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In an attempt to gain information on the propagation characteristics of pressure waves in a two-phase system consisting of gas and liquid, experiments were performed on a nonflowing air-water mixture in a range of pressures from 1.0 to 7.5 bar and void fractions from 0 to 60%. Stepwise pressure disturbancies were applied to a water column dispersed with rising air bubbles by bursting diaphragm. The pressure transients at several points down the fluid column were measured with strain gage type pressure transducers and recorded on magnetic tapes.
The nonlinearity of the pressure wave records was scarcely marked. The propagation velocity of pressure wave front down the fluid column was found almost independent of the magnitude of the pressure change applied, nor whether it was depressive or compressive. At higher void fractions where the flow regime became sluggy, the measured propagation velocities showed increasing deviation from the calculated values based on the nonslip homogeneous adiabatic model, though good agreements were obtained at lower void fractions of bubbly regime. Evidence was offered in disproof of the effect of heterogeneity due to slug regime as the preliminary step to attribute this discrepancy to the effect of slip in Part (II).

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The Langmuir vaporization and the surface ionization of LaC₂, CeC₂, PrC₂, NdC₂, ThC₂ and UC₂ from a heated graphite filament have been studied mass spectrometrically. It was found that there were present small amounts of neutral and ionic metal dicarbide molecules in addition to neutral and ionic metal atoms in the LaC₂, CeC₂, PrC₂, ThC₂ and UC₂-C systems with the exception of NdC₂-C, where neither neutral nor ionic metal dicarbide molecules were observed. The reason for this exceptional behavior of the NdC₂-C system is explained by the very small vaporization coefficients, as estimated from the measurements of neutral MC₂/M ratios and ionic MC₂/M ratios.
From the measurements of the heats of vaporization, it was surmised that the ionization potential of Th measured by the surface ionization comparison technique might be too high.

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The distribution ratios of 42 inorganic ions were radiochemically determined in a system of Diaion SKN-1 in H-form and 0∼4M hydrochloric acid, and in another system of Diaion SAN-1 in Cl-form and 1∼9M hydrochloric acid. The results are presented in an arrangement that follows the sequence of the periodic table. Several data were also obtained on Amberlite IRN-77 and -78 for comparison.

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Studies were made on the hydrolysis by water and water vapor of thorium nitrides-ThN, Th₃N₄, Th₂N₂O-and carbonitrides. All the thorium nitrides and carbonitrides were found to decompose in water below 100°C, changing thereby into ThO₂. The order among the thorium nitrides in their propensity toward hydrolysis is: ThC_1-xN_x>ThN>Th₃N₄>Th₂N₂O. Upon hydrolysis, ThN produced NH₃ and H₂, but in the case of the higher nitrides no H₂ was found to evolve.
In the reaction between ThN and water vapor, no higher nitride was produced, in contrast to the case of UN. The difference in behavior between ThN and UN was studied from the standpoint of differences in crystallographic conditions for the transformation from mononitride into higher nitrides. Through the hydrolysis of ThC_1-xN_x in water vapor, products containing C-C, C-C-C and C-N bonds, such as ethane and amines, were found in smaller quantities than for the case of UC_1-xN_x. This fact as well as the difficulty of formation of higher nitrides has resulted in a fairly simple hydrolysis behavior of thorium nitrides.

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Spontaneous two-phase flow oscillation, which can induce reactivity instability in BWR, is studied by numerical simulation, using a Fortran code. It is indicated that unstable flow is much more influenced by heat transfer characteristics than currently believed. In this study, particular attention is paid to such processes as energy storage, dissipation and transformation. Nonlinear flow oscillation of two-phase flow is dominantly governed by exchanges of heat between fluid and channel wall, which alternatively stores and releases the heat energy.

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An improved discriminating circuit which can eliminate noise counts induced in nuclear radiation counting systems by various control devices such as motor controllers has been developed. A description is given of its principle, its circuit in outline and some experimental results. The circuit is basically composed of an ordinary threshold discriminator, an undershoot detecting circuit, a temporary memory and a delay pulse generator. The temporary memory is triggered by the output pulse of the threshold discriminator and reset by the output pulse of the undershoot detecting circuit or the output pulse of the delay pulse generator. This discriminating circuit generates an output pulse when the undershoot detecting circuit does not emit its output pulse within a predetermined time from the leading-edge of the threshold discriminator output pulse. The experimental results show that this discriminating circuit can reject 97% of the noise counts in a nuclear radiation counting system, compared with the corresponding data obtained with a conventional discriminator with the pulse-height discrimination alone.

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