The thermalization parameters of light water have been measured using 'a pulsed neutron source and non-1/v absorbers (Cd, Gd and Sm). The pulsed neutron source utilizing the D-D reaction was placed at the center of an effectively infinite system of water poisoned with non-1/vabsorbers. The time dependent capture γ-rays from these absorbers were detected by a NaI(T1) scintillation counter. The neutron thermalization time constant of right water was determined to be 5.3±0.3μsec from the difference of the decaying reaction rates of the γ-rays, expressed asthe sum of two asymptotical exponential components. The resulting value was larger than that of Moller's experiment (4.1±0.4μsec), but agreed fairly well with the theoretical value of 5.6μsec, calculated by Hoshino based on the Nelkin model. A supplementary experiment was performed using thick neutronic filters of Cd and Ag.

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A new method of electronic collimation is reported. The counter is composed of two proportional counters with cathodes arranged end-to-end on a common axis occupied by a common wire anode. The whole is placed in a methane filled envelope. Energy signals taken from the center wire are gated by coincidence signals between the pulses taken from the two cathodes. By such an arrangement only particles which are parallel to the center wire are detected or analyzed. The method is applicable to gas recoil neutron spectrometers and permit the conven-tional collimator to be dispensed with.

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Experience involving basic concept of nuclear criticality has shown that there are many complex effects involved, some of which have been little studied and are not well understood. One of these involves the effect of added scatterers on criticality.
A study has been made of the effect of added scatterers (O, C, N) on criticality by means of transport theory calculations utilizing the DTE-IV codes. This study pertains to plutonium compounds likely to be encountered throughout the nuclear industry - in fuel processing and fabrication operations. It is shown that in some cases of undermoderated thin slab with hydro-genous reflectors, the effect of added scatterers can cause an increase in the critical dimension contrary to the usual expectation that the size should be reduced in such cases.
Interpretation of the reswksrobtained for water-reflected and nickel-reflected slabs, including scatterers added homogeneously to the core region, contribute to a better understanding of the observed effects. The dominant factor causing the increase in slab thickness is the decrease of neutron leakage into the moderating reflector.

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The role of the water of crystallization and the effects of the cations on the initial reten-tion and the thermal annealing of 51Cr were investigated for chromates of potassium, sodium, manganese and thallium, which were irradiated at dry ice temperature. It was found that thermal annealing took place below room temperature. A hitherto unnoted effect found in the thermal annealing process of sodium chromate quadrahydrate was dehydration during the thermal annealing process.

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A series of dicarboxylic acids of Li-(CH₂)_n(COOLi)₂, n=05, i.e., Li-oxalate, -malonate, -succinate, -glutalate, -adipate and -pimelate, was irradiated with mixed radiations in a nuclear reactor. The subject of study was the decarboxylation and the reaction of labelling with T atoms brought about by the exposure of the dicarboxylic acid lithium salts to neutrons.
The T-labelled hydrocarbons were determined by radiogaschromatography, while gaschro-matography was used to measure macroscopic amounts of compounds. The gaseous products of radiolysis produced from the neutron irradiation of dicarboxylic acid lithium salt were CO₂, CO and hydrocarbons.
The yield of CO₂ from the different dicarboxylic acid lithium salts was higher than obtained from γ-ray irradiation, and decreased with increasing number of methylene groups in the original salt. Also, while with y-radiolysis, CO is only generated in negligibly small amounts, it was found quite significant in the present case of neutron irradiation. The yield of tritiated hydro-carbon was proportional to the number of methylene groups in the salt molecule. Hydrocarbon was mainly produced by the decarboxylation of the original compounds. Several kinds of degradated hydrocarbon were also observed from the mass peaks as also from activity peaks.

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Several problems encountered in the measurement of heat capacity at high temperatures by the laser flash method are discussed with the view to improving the accuracy of the measure-ments. The samples were disks of sintered alumina. The heat capacity measurement was carried out at temperatures ranging from 25°C to 700°C. The energy of the laser beam was determined with the use of a silicon photoelectric cell and a standard sample of pure iron. The experimental results are compared with the NBS standard data for alumina. Agreement is seen within experimental error, estimated to be ±1.5 %.

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Pressure propagation phenomena in regularly spaced two-phase layers is discussed from theory. The value for sound velocity becomes that usually expected for a homogeneous com-pressible medium in the limiting case where the thickness of each layer is small compared with the wave-lergth. There must be a sufficient number of layers for the homogeneous concept to hold. Otherwise dispersion is expected.

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