In the previous paper, we have reported the results of basic experiments to fix tritiated water using the hydration of cement, and found that most tritiated water transfers to surrounding water, even if it is incorporated using the hydration of cement. In this report, we tried to apply a simple compartment model to the tritium transfer curves reported in the previous paper, which represent the phenomena that most water containing tritium is exchanging with a surrounding water, regardless of its forms, i. e., a crystalline water, free water and so on. We divided a solidified cement into three groupes with respect to the exchangeability of water, i. e., a compartment of fixed water, of compositions except water, and of exchanging water. We developed a simple compartment model under the assumption that the water in the third compartment is exchangeable with the sorrounding water with a certain exchanging volume rate E, not altering by time. The transfer curves calculated with the model contains unknown parameter, E. By the method of least squares, varying the values of E, we could obtain most approximated transfer curves of tritium to those obtained by the previous experiments. In the result, we knew that the simple compartment model is applied to the tritium transfer curves reported in the previous paper.
Radiation shielding effect against γ-rays from radioactive noble gas cloud resulting from a major reactor accident was investigated for three typical residential houses in Japan; prefabricated, wooden and ferroconcrete houses. The shielding factors of the houses, the ratio of indoor dose rate to outdoor one, were estimated for the submersion and cylindrical plume trailing overhead, which contain monoenergetic γ-ray sources or γ-emitting noble gas radioactive nuclides. The shielding factors against the noble gas cloud decrease gradually with the release delay time and maintain the minima after 50 hours while 133Xe predominates in the cloud. Neither the mixing of iodine nuclides in the cloud nor the cloud shape affects significantly the shielding factors. Finally the shielding factors for the use of emergency planning were proposed as 0.4 for ferroconcrete residential houses and 0.9 for other ordinary residential ones.
In order to clarify the relation between the size of particles and their retention sites in the tracheal wall, Wistar rats were intratracheally administered four kinds of tracer particles, i. e., colloidal carbon of 0.03μm, colloidal gold of 0.01μm, and fluorescent latex particles of 0.27 and 1.24μm in diameter. The distribution of the tracer particles in the distal trachea was examined by light microscopy 3h and 3 days after instillation. The uptake of particulates by the epithelial cells of the trachea seemed to be rare events, especially for latex particles of both sizes. Only for colloidal carbon and colloidal gold, a slight uptake by the epithelial cells was observed 3 days after instillation. On the other hand, all the four kinds of tracer particles were buried in the tracheal wall 3 days after instillation. The latex particles were mainly situated in or beneath the basement membrane of the epithelial cells. The distribution of colloidal carbon and colloidal gold seemed to be a little broader than that of the latex particles but otherwise similar to it.
A radon daughter monitor with a build-up and decay method (B. D. R. D. monitor) was developed to investigate the behavior of short-lived radon daughters indoors and outdoors. The monitor was available for long term continuous measurements with simple maintenance every a month. The sensitivity of the new monitor was compared with that of the monitor with a decay method (D. R. D. monitor), which has been called Thomas method. As the results, it was found that the B. D. R. D. monitor is more better than that of the D. R. D. monitor in assessment of RaA having the shortest life time among radon daughters. It was found, also, that the plateout effect of radon daughter gave slight and unavoidable errors to the B. D. R. D. monitor through the process of both the counting loss and the enhancement of background level. It was concluded that even if the B. D. R. D. monitor had those disadvantages it was very useful instrument to measure individual radon daughters in the natural environment.
In order to carry out the measurement of low-level tritiated samples, such as environmeantal ones, liquid scintilation couting method is mainly used. In this method the back-ground water, tritium free water, plays a vital role. Generally, deep well water or deep sea water are adopted, but it is difficult to prove clearly that the waters do not contain any tritium. On this account, we developed an apparatus which synthesizes “tritium free water” from natural gas. The gas and oxygen mixed with argon were circulated in a closed system, the gas was oxydized to water by means of paradium catalyst, and synthesized water was trapped by a column filled with molecular sieve. The examination results on the synthesized water, which was produced by using the commercial oxygen gas products, indicated an unexpected level of tritium, 6.8±1.6pCi/l, and it was clarified that the presence of tritiated methane in the oxygen caused it. By this reason, we concluded that using more purified oxygen and improving the system would bring us “tritium free water” which was practically fit for use.