The power noise measurements were carried out on the Kyoto University Reactor at various reactor power levels under natural convection for two kinds of core configuration with different temperature coefficients of reactivity. Analysis of the results revealed strong noise in the low frequency region at higher power levels, even with a core configuration of essentially zero temperature coefficient of total reactivity.
A conventional theoretical model assuming a white noise input in reactivity and a reactor trans-fer function with temperature-reactivity feedbacks was adopted for comparison with the observed data, but it resulted in considerable disagreement at higher power levels.
As a result, it is concluded that there must exist other power effects not yet clarified in the reactivity feedbacks or in the noise inputs to the reactor, which are responsible for the experimental noise spectrum distortion in the low frequency region.

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A silicon semiconductor radiation detector has been used to study the diffusion of Au into Cu in the temperature range 356°-440°C by detecting elastically scattered deuterons. In the above temperature range, the measured diffusion coefficients of An into Cu are somewhat larger than the results of Sippel's experiments, while the activation energy of the diffusion is roughly the same.
Diffusion lengths (=√Dt) as small as 2×10^-7cm can be measured by the present method, which may make it possible to detect the effects of radiation damage on diffusion phenomena in metals.

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Flux monitoring in the specimen chamber of FGRL was carried out by directly and continuously reading with a γ-ray spectrometer the content of ¹⁶N in the primary cooling water produced by ¹⁶O(n, p)¹⁶N reaction within the cooling jacket of FGRL. ¹⁶N generation is not influenced by γ-ray build-up in the reactor nor by the temperature in the specimen chamber. The detector can be simply set outside the pipe through which the cooling water flows, because the high energy γ-rays (6.13MeV) emitted during the ¹⁶N decay easily penetrate the pipe wall.

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The purpose of the persent work is to evaluate the heat of formation of uranium sesquinitride, U₂N₃. The U2N3 phase is known to form a single solid solution with UN₂, while the U2N3 compound with minimum N/U ratio is in equilibrium mith UN under a given condition of temperature. The heat of formation for the terminal U₂N₃ has been calculated from measured pressure of decomposition from U₂N₃ to UN, by Gross, et al., Lapat, et al. and Bauer, et al. In the present work, the decomposition pressure was measured by a simple Sievert apparatus with an oil manometer. From the nitrogen pressure-composition-isotherms obtained by Lapat, et al., the interaction energies for U-U, U-N and N-N were calculated statistico-thermodynamically. Using these values, the heat of formation for the single phase U₂N₃ was determined to be
ΔH⁰(U₂N_3+x)=-172.2-48.9x+25.4x²kcal/mol.

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Plutonium nitrate solution stored for long after separation from uranium and fission products by anion-exchange and containing a large amount of hydroxyl-amine hydrochloride used as eluent, was repurified by anion-exchange. Radiochemical determination of plutonium isotopes-both in the purified plutonium solution and waste solution - was also studied.
The results were as follows;
(1) Pu(IV) was adsorbed on anion-exchange resin (Dowex-1×2, 200-400 mesh) in 7.2N nitric acid solution at about 60°C, and was eluted with 0.35 N nitric acid.
(2) Plutonium was recovered with a yield of 97%.
(3) High purity plutonium was obtained, leaving 241Am in the waste solution.

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An improved n-γ discriminator circuit has been devised, which compares the peak amplitude of Owen pulses with that of the coincident linear pulses produced by an organic scintillation counter.
The scintillation pulses induced by γ-rays have been eliminated to an extent of more than 95 % in ranges of electron energy up to 10 MeV and to about 80 % between 10 and 12 MeV.

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A method has been developed to enrich ^87mSr by (n, 2n) reaction, as a preliminary study for the enrichment of ⁴⁷Ca. The method is based on capturing the recoils from a scattered target into a solidified phase of several percent by weight of gelatine in water. A fine strontium carbonate pow-der is suspended uniformly in gelatine phase, and irradiated with neutrons of 14 MeV. The results show that 4-23% of the induced 87mSr activities were separated into the gelatine phase, with an enrichment factor of 4-16.

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The oxides of scandium, yttrium and all elements from lanthanum through lutetium, except promethium, were irradiated for 1 hr with bremsstrahlung γ-rays converted from a 20 MeV electron beam, and the radioactive species produced as a result have been examined on the basis of photonuclear reactions, their yields, and their applicability to activation analyses. The sensitivity and selectivity of the proposed method are discussed from the data thus obtained.
The (γ, n) reaction was predominant for most elements, and at least 28 product nuclides have been identified. A number of other (γ, 2n) reactions have also been observed.
The yields of the (γ, n) reactions have been estimated for the lanthanide rare earths through measurement of the resultant activity to be about 107/mole•R and somewhat more than 10 % smaller for the corresponding (γ, 2n) reaction. Reactions with charged particle emission contributed only a small fraction in the observed radioactivity.
Extraneous activity arising from neutron capture was also measured; these activities could be reduced considerably by encasing the sample in boron.
The lower limits of detection averaged about 1μg for most of the rare earth elements.

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A solvent extraction method using a mixture of 0.1M thenoyltrifluoroacetone and 0.1M tributylphosphate in carbon tetrachloride has been developed for the separation and purification of ²²⁸Ac in ²²⁸Ra solutions. The ²²⁸Ra was first purified by a preliminary extraction cycle. The ²²⁸Ac which had accumulated int his ²²⁸Ra fraction after the purification was separated and purified by a second solvent extraction cycle. Since commercially available ²²⁸Ra solution very often contains ²²⁶Ra, the γ-radioactive decay products of the ²²⁸Ra have to be carefully removed. The ²²⁸Ac thus prepared was found to be pure enough for use as tracer.

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