The distribution of fission fragments recoiled from a thick layer of uranium oxide into aluminum was measured with the application of an anodizing technique to strip layers from aluminum. Details of the procedure are described. The distribution thus determined gave the recoil ranges of the fission fragments: They were 4.06 mg/cm² for ⁹⁵Zr-⁹⁵Nb and 2.67 mg/cm² for ^l40Ba-¹⁴⁰La. The correction factors for these ranges to account for the scattering effect in the uranium oxide layer were estimated. The measured recoil ranges are compared with those previously reported by a number of investigators, and with calculation by semi-empirical formula.

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A fuel rod scanner with an automatic decay correction system was manufactured to measure the reactor power density distribution by the γ-activity from an irradiated fuel rod.
The detection head is a scintillation counter surrounded with Pb shield. A fuel rod travels on this head by the feed mechanism operated by compressed air force. Main advantages are that this mechanism does not give any oscillation to the fuel rod in moving and settles the measuring point accurately within ±0.01 mm.
It is hardly possible to calculate the correction for decay of the fission product because it includes many kinds of decays and it has decay constant varying with time. Therefore, an automatic correction for decay time is highly desirable. A system of automatic decay correction, combining an automatic fuel rod scanner and electronic circuits, is used which effects the remote and automatic counting with minimal personnel.
The effect of background counts in measuring and monitor channels and the pulse pile-up at high counting rate in electronic circuits are discussed in detail. In case of predominant background counts, it is preferable to make a measurement so as to satisfy the following equation,
BM/B=P/Nprii,
where BM, B are background counts in monitor and measuring channels respectively and P, NiPri a preset count in monitor channel and an observed count in measuring channel.

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U, Np and F.P. in neutron irradiated uranium oxide were separated from each other using focusing chromatography. Individual nuclides were determined by γ-ray spectrometry. As complex forming agent, 1.0M lactic acid and 0.05M nitrilotriacetic acid (NTA) were tried, and various mixtures of hydrochloric acid and sodium chloride as complex decomposing agent.
The efficacy of the forming and decomposing agents for the separation was observed with various solutions of electrolytes. In all cases, Tc, Mo, Ru, Rh, I, Zr and one fraction of Np migrated toward the anode. As the hydrogen ion concentration of the complex decomposing solution was decreased, these nuclides became more easily separable. Te and a small amount of Np generally remained in the area of the spot where the sample had been introduced. Sr and Ba always migrated toward the cathode. Rare earth elements were sensitive not only to the kind of complex forming agent used but also to the pH value of the decomposing solution. Np manifested three different modes of focusing characteristic, their proportions varying with the conditions of the separation system.
The concluding result was that the system of 0.1 M sodium chloride-1.0M lactic acid was found the most suitable for separating these multi-component mixtures.

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The behavior of radiation induced gas bubbles in Al-Li alloys was observed, by mess of 3H autoradiography. The autoradiographs were compared with photomicrographs of the corresponding areas. Autoradiography proved to reveal the gas bubbles in the alloys more distinctly than photomicrography.
It was found that the bubbles first appeared at the grain boundaries and subgrain boundaries, and there also appeared depleted zones along the grain boundaries. This was followed by crystallo-graphic alignment of the bubbles when heated to higher temperatures. In the case of large gas concentrations, bubbles as large as 5 μ in diameter were observed in specimens heated for 1 hr at 500°C. Bubbles precipitated along the boundaries of recrystallized grains in a specimen of irradiated Al-2.7 W/OLi when it was tension stretched and then heated for 1 hr at 300°C.

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A refinement on the calculation of the effective cutoff energies of neutron filters has been made by taking into account the scattering and higher resonances of the filters. The effect of scattering is found to be considerable, especially in the case of resonance detectors. With Sm and Gd filters the higher resonances introduce marked deviations of the cutoff energies from those calculated without taking their effect into account. These two factors of scattering and higher resonances cause the epithermal neutron flux from the 1/E-spectrum to strongly affect the cutoff energies.

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Nb and Nb-V alloys are promising as high-temperature reactor materials. For this reason their oxidation behavior was studied in the temperature range 485°-735°C. The specimens were prepared by electron-beam and arc melting. The work included kinetic studies of the oxidation as well as X-ray studies of oxide films. The oxidation reactions of Nb and Nb-V alloys were found to have a very peculiar temperature dependence. The complex oxidation behavior shown by the individual Nb and Nb-V alloys is suggested to he due to the formation of oxide layers with differing compositions in different temperature regions. The formation of a double oxide NbVO₄ was identified, and the structure was examined by X-ray diffraction.

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Breeding ratio, effective multiplication factor keff and sodium-void reactivity effect of Pu-U fast reactors having a 3, 000 l core volume are investigated as functions of burn-up. Following results are obtained.
(1) Initial breeding ratio does not fail to be a measure for roughly estimating breeding character.
(2) By charging Pu fuel in the internal blanket situated inside core region, heft. of the system remains almost constant along with burn-up.
(3) The variation of sodium-void reactivity due to fuel burn-up of the above system does not seem to be serious.

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