An analysis was made of a light water moderated lattice based on few group diffusion calcula- tions. The lattice under investigation consisted of 468 fuel rods in a square lattice arranged in a cylindrical core of 22.46 cm effective radius and 127.2 cm core height, with a water to fuel volume ratio of 2.918. The fuel was 2.02 % enriched UO2, clad in 0.8 mm thick aluminum tube.
The theoretically calculated values for thermal, epithermal and fast neutron flux distributions, as well as the effective multiplication constant λ of the lattice, were compared with experimental data. After detailed analysis of the problems encountered in the course of the study the value of 0.9935 was determined for λ. Uncertainty in the nuclear data for fast neutrons would appear to constitute the greatest factor of error in λ. The discrepancies between the calculated and experi- mental activation distributions of the thermal, epithermal and fast neutrons amounted for about 20, 10 and 15 %, respectively, in the reflector region adjoining the core. The fact that these discrepancies cannot be removed by multigroup P1 calculations would point toward insufficiency of the diffusion or P1 calculation this region.
It was also concluded that the following items could not be neglected without causing an error in λ of more than 0.3 % in the particular lattice under investigation :
(1) Heterogeneity in the fast neutron energy region.
(2) Intra-cell change of thermal neutron spectrum.
(3) Macroscopic spectral change near the core-reflector interface.

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Changes to plutonium extraction properties brought about through irradiation of 30 v/o TBP (Tri-n-butyl phosphate)/ kerosene and 5 v/o alkylamines/kerosene modified with lauryl alcohol were studied in such respects as extraction, scrubbing and stripping characteristics in nitrate media.
The alkylamines examined were tri-n-octyl amine (TOA), N-cyclohexyl dilauryl amine (N-CHDLA) and Amberlite LA-2 (LA-2). These extractants were irradiated to the extent of 10⁸R by ⁸⁰Co γ-ray, prior to extraction.
Marked changes with irradiation were observed in plutonium extraction performance with the TBP system tending to bring losses of plutonium, but very little change was found to occur with amine systems.
Calculation of the single stage decontamination factors of fission products from plutonium proved that separation deteriorated with irradiation in the TBP system but hardly changed in the amine systems. From these findings, tertiary amines, especially N-CHDLA, can be judged superior to TBP for the direct recovery of plutonium from irradiated fuels, a process that has to be carried out under high irradiation.
The phase separation time after mixing in the extraction stage varied very little with irradiation, and no formation of emulsion occurred in the extraction of tracer plutonium with either irradiated TBP or amines.

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An 8-quinolinol-extraction method has been applied to separate ⁹⁵Zr-⁹⁵Nb or ⁹⁵Nb from fission product mixtures and/or irradiated uranium. Radiochemically pure nuclides can be separated simply and rapidly from either origin. In the separation of ⁹⁵Zr-⁹⁵Nb, the extraction is made from a solution of pH 4.5 to 5.5, containing acetate as masking agent. ⁹⁵Nb is extracted from a solution of pH 4.8 to 5.2, containing fluoride as masking agent, in the presence of uranium. ⁹⁵Nb can be separated from ⁹⁵Zr and other fission products by extraction from a solution of pH 5.3 to 8, containing EDTA as masking agent. In these cases, after the first extraction, the chloroform solution should be washed with water to remove any remaining extraneous uranium or fission products. The addition of a small quantity of sulfite is required to prevent the extraction of ¹⁰⁸Ru.
The method can be also used for the separation of the short-lived nuclides, ⁹⁷Zr-⁹⁷Nb or 97Nb, from irradiated uranium.

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Neutron activation analysis of thorium in mineral springs and coastal waters is reported. After preliminary concentration of thorium in natural waters with coprecipitation of ferric hydroxide, the samples were irradiated in JRR-2. The ²³³Pa produced in the target materials was radiochemically separated by solvent extraction with DIBK-hydrochloric acid system, and the electrodeposited source was counted. The chemical yield was verified by ²³¹Pa tracer. The reliability of this method was ascertained by the use of standard rock G-1. Values of 0.01 to 0.5 μg/l were obtained for thorium content in waters from several springs in Japan. These values are very much lower than those previously reported, and the characteristics varying with region are reported. Some geochemical considerations with regard to the origin of uranium in the springs of such localities as Asanbara and Misasa are discussed.

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An elaborate calibration of BF₃-gas-filled proportional counters with and without moderator was made for isotropic neutron fluxes. The effective sensitivity of a hare BF₃ counter in a nondiffusing medium was determined by means of a calibrated indium foil. The flux-depression effect in a diffusing medium was experimentally evaluated. Details of the experimental techniques and results are described. For the measurement of fast neutrons, energy dependence of sensitivity of two differently moderated counters was determined in the energy region from 1 eV to 10 MeV. Angular dependence of sensitivity of the moderated counters and its dependence on neutron energy are also described.

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