The detection of anomalous coolant boiling in non-boiling reactors is an important problem for assuring reactor safety. Acoustic techniques are an effective means of such detection. Reliable detection of boiling postulates frequency spectra peculiar to boiling, and if, moreover, the location of the boiling sites is to be determined, it should further be necessary to distin guish noise emanating directly from the point of boiling. The purpose of this paper is to find out experimentally whether the often observed resonance-like peaks of boiling noise are associ ated with the actual collapsing of bubbles or due to the resonances of the container system.
Localized nucleate boiling was generated by electric heater immersed in a water tank. Two hydrophones were suspended in the water at different distances from the heater and the acoustic signals detected therewith. The signals thus gathered were conditioned and processed in cross-correlation functions.
When the signals were processed to isolate those in the frequency range containing con siderable resonance-like peaks, the cross-correlation peaks were all found near the zero-lag position irrespective of the distance of the detectors from the noise source, indicating that the signals were mainly due to the resonance of the container system. When noise signals of frequencies higher than the resonance frequencies were taken up, the cross-correlation peaks shifted according to the difference in distance from source represented by the two detectors, and the shift, moreover, agreed quite well with the calculated values. Thus, signals not containing resonance frequencies should serve effectively in locating the boiling sites by triangulation technique.

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The isotopes of transplutonium elements were produced by irradiation of 10.5 mg of ²⁴¹AmaO₂ in the Japan Materials Testing Reactor during the period May 1970 through June 1971. Transplutonium elements were separated from plutonium, fission products and cladding materials by a combination of precipitation and ion exchange methods. Americium, curium and cali-fornium were mutually isolated by ordinary procedure. Plutonium-238242, americium-241 243 and curium-242245 were detected in the plutonium, americium and curium fractions, respectively. The ratios of the amounts present of these isotopes were determined by mass spectrometry. It was not possible to identify ²⁴⁹Bk in the berkelium fraction owing to the interference from other β-ray emitting nuclides. In the californium fraction, both spontaneous fission and a-activities due to ^{250, 252} were observed.

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Based on requirements felt in the domains of health physics and radiation protection, a study was made of the accuracy and sensibility of different practical methods utilized in dosimetry. The ionization chamber, the NaI true spectrum method, the method relying on the proportional counter, and soil sampling, were applied to measurements in various environments and in constant irradiation field. The three techniques first named yielded results agreeing quite well with each other in a field of constant exposure rate.
The results obtained with soil sampling, using a Ge(Li) measuring system indicated that the small amount of ¹³⁷Cs radionuclide remaining in the soil tended to give values somewhat higher than given by other methods.
The small difference in incident radiation entering a detector between one placed in natural environment and one shielded with thin concrete could be distinguished by the NaI true spectrum method.
The method utilizing the proportional counter also gave quite good results considering its small effective volume.
In respect of both accuracy and sensibility, it can be concluded that the NaI true spectrum method is the best among the techniques taken up in the present study.

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The rate of removal of oxygen from inert gas by metallic getter is measured continuously, and the dilution model is adopted for explaining the rate of purification. The rate of removal of oxygen increases with flow rate. It is found that hydrogen and water vapor present in the inert gas contributes very effectively to reducing the oxygen partial pressure. The rate of removal of oxygen with a titanium getter increases with temperature below about 800°C, but levels off above about 800°C.

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