[en] For investigating property changes of ceramics by radiation to study radiation resistance and modification, changes of dielectric loss tangent at ultra low frequency region (0.1 to 100 Hz) and microwave region (0.1 to 10 GHz) were examined by irradiating ⁶⁰Co γ-ray to alumina ceramics. As a result, it was found that the dielectric loss tangent in ultra low frequency had nearly same slope in graph of irradiated sample as that of non-irradiated one, and showed to decrease with decline of test frequency even in non-irradiated alumina ceramics. And, it was also found that in the alumina ceramics irradiated 300 KGy of γ-ray, the test dielectric loss tangent increased in a wide range in comparison with that of non-irradiated one. On next, as a result of measuring the dielectric properties at microwave frequency ranges from 0.1 to 10 GHz, it was found that radiation effect was rarely found and the alumina ceramics was a very stable material as well as testing at frequency ranges from 100 Hz to 15 MHz. (G.K.)

[en] The level gauges using sealed radiation sources have been utilized for pulp and chemical industries, however, for those gauges, transmission type gamma sources are used, which require considerably large radioactivity, and it hinders the spread to medium and small enterprises. Recently, Cf-252 has become easily available, and various He-3 counters are on the market, consequently, the scattering type level gauges combining them have been examined. With the level gauges of this type, the judgement of level can be made sufficiently with the Cf-252 below 3.7 x 10⁶ Bq, therefore, if the practical instruments are made, they seem to spread into medium and small enterprises because of the safety and the chief handling radiation being unnecessary. For the purpose of developing and manufacturing for trial this scattering type level gauge, the basic experiment was carried out to examine the effects of the change of salt content and the thickness of vessels and the effect of scattering materials. The possibility of the on-off operation as level gauges was also examined. The experimental method and the results are reported. The count considerably decreased with increasing salt content. Scattering materials worked effectively to increase the count. (Kako, I.)

[en] The surface potential, surface charge density and thermally stimulated current of the FEP films which were changed to electrets by irradiating 170 keV electron beam were measured, and the relationship among their measured values was investigated. As the result, it was known that the mean value of surface potential was proportional to surface charge density. Besides, according to the results of measurement of surface charge density and thermally stimulated current, also positive charges seemed to exist in the samples irradiated with electron beam. The measurements of surface potential, surface charge density and thermally stimulated current are reported. There are the FEP film surfaces irradiated with electron beam on which potential distributed largely changing from positive to negative, and on which only negative potential distributed with relatively small change. Thermally stimulated current is due to the polarization in samples and the relaxation phenomena of trapped charges. As FEP is assumed to be without polarity, the latter cause is conceivable, and also positive charges seemed to exist. (K.I.)

[en] Short communication

[en] Short communication

[en] The measurement of environmental radioactivity in Tokyo Metropolis was carried out. The objects of measurement were rainwater, atmospheric floating dusts, spatial dose and the activated sludge in sewage treatment plants. Rainwater, atmospheric floating dusts and spatial dose were analyzed mainly considering radioactive fallout, and activated sludge was analyzed mainly considering radioactive medical matters. For the analysis of nuclides, a Ge(Li) semiconductor detector was used, and spatial dose rate was measured with a DBM type dose rate meter. In activated sludge, the nuclides used for radioactive medicines were found, but in rainwater, atmospheric floating dusts and spatial dose, particular abnormality was not found. The objective of this investigation is to collect over long period at definite time and definite points the data on environmental radioactivity in Tokyo, thus to grasp the level of normal values, and in abnormal case, to clarify the cause and to evaluate the exposure dose. The instruments used, the method of measuring each object and the results are reported. (K.I.)

[en] Short communication