Fluorine-18 was prepared by neutron irradiation of lithium carbonate in the reactor JRR-1. Five grams of lithium carbonate was irradiated for 2 hr with a thermal neutron flux of 6×10¹¹ n/cm²/ sec. An alumina column was used to separate ¹⁸F from the irradiated material. The various factors which affect the separation were studied, and purity and specific activity were determined. About 90μc of ¹⁸F per gram of lithium carbonate was prepared by this method with a chemical yield exceeding 80%. The prepared ¹⁸F was pure enough radiochemically but contained a small amount of lithium and aluminum. The specific activity was about 0.5 mc/mgF.
The chemical form of the 18F obtained by the above method was studied by paper-chromatography. A sample was developed on filter paper by the ascending method using butanol-methanol-water mixture as solvent, and the distribution of ¹⁸F radioactivity was determined. From the results of the paper-chromatographic study, it was found that most of the ¹⁸F existed in the form of fluoride but about 16% in other form possibly a complex with aluminum.

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The electric potential drop near the electrode surfaces in MHD power generators is studied theoretically by considering a simple model, in which the current flows in the direction normal to the electrode surfaces. In order to simplify the situation so as to permit analytic solution, the idea of a "boundary layer" near the electrodes is introduced, and the problem is treated entirely macroscopically, wherein the following assumptions are made:
(1) The electrical conductivity is constant.
(2) The Hall effect and the induced magnetic field can be neglected.
(3) The behavior of the flow in the boundary layer may be described by equations for laminar flow.
(4) The temperature variation in the boundary layer perpendicular to the electrode surfaces may be neglected.
The theory predicts that the magnitude of the electric potential drop near the electrode is of the order of 10 V in typical MHD power generators.

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The neutron life has been determined in a D₂O system by combining observation of the inherent fluctuations which occur in the neutron population and reactivity measurements by period method.
The ratio of variance to mean number of counts was measured as a function of counting intervals. Short counting-time intervals were chosen in the experiment to eliminate contribution of delayed neutrons. Also, the variance was measured in the subcritical state, to eliminate the counting loss due to the dead time of the detector.
The decay constant for the critical state has been determined by extrapolation of the observed relation between the decay constant and reactivity.

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Isotopic ratios of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am in a plutonium sample were approximately determined by means of combined α- and γ-ray spectrometry without chemical separation of americium from plutonium. The intensity of α-ray followed by internal conversion was determined by measuring the intensity of LX-rays. The ratio of ²⁴⁰Pu to ²³⁹Pu was obtained from the ratio between the α-ray intensity thus determined and the total α-ray intensity from the two nuclides.

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Since aluminum is widely used in reactor construction, the recoil ranges of ²⁷Mg and ²⁴Na produced by the (n, p) and (n, α) reactions play an important part in evaluating the amount of activity in the coolant of swimming pool type reactors. These recoil ranges however do not seem so far to have been studied in any great detail. Acrylic acid resin vessels containing aluminum sheets immersed in water were irradiated in the H.T.R. (Hitachi Training Reactor), after which the activity from the water was measured by β-γ coincidence. Background activity was determined by preparing blank water samples in which aluminum sheets were soaked for the same time interval without irradiation. Argon-41 activity was corrected by taking the decay curves from each of the coincidence channels. Aluminum foils were also irradiated dry and counted to determine the reaction rate. Recoil ranges of ²⁷Mg and ²⁴Na thus determined were 4.18×10^-5 cm and 1.37×10^-4 cm respectively, which agreed well with calculated values.

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In order to measure reactivity from instant to instant during reactor operation, real time computation based on reactor kinetic equations must be made.
The authors developed some reactivity meters capable of such computation based on the analog computer technique. After their characteristics were checked by an analog computer and a kinetic simulator, they were applied to reactor experiments and operation. It was found that the reactivity meter method for measurement of reactivity worth (especially for control rod calibration) is better than other current methods, and the reactivity meter can also serve as a tool in nuclear instrumentation of reactors for its ability to indicate reactivity even in reactor start up conditions.

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