In JAERI, Kodak Personal Neutron Monitoring Film, Type A-NTA film-has been used to estimate personal exposure dose due to fast neutrons. Track fading, spectrum of track after fading and prevention of track fading of the NTA film were investigated at various relative humidities of the atomosphere. The phenomenon of track fading of the NTA film was remarkable at higher relative humidity and the fading curves consist of two components of exponential function. Relationship of lineality between dose and number of track was found to be still maintained in the advance of fading. In addition, dose dependence of fading was not observed. As relative humidity and storage time increases, track length became shorter and grain density of track decreased. Track fading is prevented by wrapping the NTA film with vinylidene chloride film and putting in the badge case.
The purpose of the present investigation was to extend the study on the plutonium skin contamination and decontamination which was reported in the first paper of this series. In this study, the preparation of the contaminated samples for autoradiography was carried out by frozen-dried method and the autoradiography was done by dipping method. Dispersed and aggregated plutonium were observed on the pig skin as contamination forms. The ratio of the aggregated to the total contamination increased with contaminating time. The residual contamination on the samples which were decontaminated by synthetic detergent involved almost aggregated plutonium, while by EDTA or sodium hypochlorite decontamination, the reverse happened. The percutaneous absorption through the intact skin was not found by shorter time contamination but it was observed through a broken stratum corneum by 60 min. contamination.
Samples of liquid milk from Hsinchu, fifteen varieties of powder milk from Taiwan, and imported powder milk from Holland, Denmark, United States of America, Japan, and Australia have been measured for their 90Sr and 137Cs contents. The average 90Sr and 137Cs content of Hsinchu milk is 2.5 pCi/gCa and 6.4 pCi/gK respectively between October 1968 and July 1969. The increase in the average level of 90Sr by a factor of 1.4 as compared with that in 1964 is attributed to the nuclear weapon tests at Lop Nor. The 90Sr and 137Cs contents in the Australian powder milk is found to be about the same and in the North European and American powder milk about two or three times that in Taiwan powder milk.
A technique of solidification in bottle had been desired of plutonium liquid wastes for safe transportation and storage. Experiments were thus carried out for studying the physico-chemical properties of materials concerning a solidification of the wastes. It has been found that vermiculite was superior to water absorbability, water permeability, acid resistibility and plutonium sorbability, and that plaster was excellent in solidifying ability over the wide range of acidity. And that the mixture of vermiculite and plaster with an optimum composition was useful for the solidification of the wastes. In conclusion, the best result is obtained by pouring the wastes into the mixture consisting of vermiculite and plaster in 1: 1 by volume, and hereupon, volume of the wastes poured is limited to half compared with volume of the mixture. Furthermore, the practical procedure of solidification in bottle and safety controls regarding storage disposal of the resultant wastes have been described.
The principle of whole-body counting is widely applied to various fields of science. Much emphasis has so far been laid on the detection of a very small quantity of radioactivity, thus strenuous efforts having been made to improve sensitivity and energy resolution of equipments. In order to accomplish the purpose of radiation protection effectively, however, the following three points become more important. Namely, (1) Clearifying the role of whole-body counting in the radiation protection service. (2) Giving the whole-body counter the function as an individual monitor of internal exposure. (3) Utilizing the whole-body counter more easily and frequently, feeding the result back to the radiation protection service rapidly. The present paper gives some basis for the argument that a simplified whole-body counter can meet these requirements satisfactorily, and that effective and economical radiation protection can readily be accomplished by this simplification. The basic properties required of the simplified whole-body counter for the monitoring purpose are considered in view of efficiency of detectors, its mechanism, and the way of utilizing it in the routine monitoring program. As an example, the paper describes the outline of the simplified whole-body counter intended to be installed in a certain nuclear power station.