This paper reports preliminary studies on the mechanism of the mortality reduction effects in sublethally irradiated mice by ad-ministration of zinc at the high concentration. At first, accumulations of65Zn in non-irradiated mice, which were orally administered with the artificial diet containing the radio-tracer and the stable metal at the high cocentration (1000 ppm), were investigated, and compared with those in mice which were administered with the artificial basal diet containing the tracer (control) . Then the irradiation effects of60Co gamma-ray at the sublethal dose on the accumulation were studied. The concentrations of zinc in whole body, tissues and organs of non-irradiated mice which were administered with the former diet were 2-fold higher than in the mice which were administered with the latter diet (control) . But the accumulation of the tracer was affected by the irradiation, i.e. the concentrations in tissues and organs (except for blood and bone) of irradiated mice were lower than those in non-irradiated mice. However, the concentration in spleen of irradiated mice was remarkably higher than in the other tissues.
The small-volume electrolytic enrichment device was developed to concentrate the low-level tritium in water samples such as the combustion water of soil or vegetation in the environment. The system was controlled by a personal computer. The reliability of this device was checked by comparing the results obtained by this system with those of the conventional large-volume one. The same seawater samples in the Pacific Ocean that had been used in case of the large-volume one were also used in this case. The results obtained showed good agreements within the statistical error of one sigma. The detection limit of the tritium concentration by this system is about 0.7 TU with 50% C.V., and it is effective enough to measure the lower tritium concentration of 1 TU or so.
The control scintigrams of four kinds of organs in rats with99mTc were presented by the Kaneko's method using the improved pinhole collimator. All images were high resolutive, and the fine structures of the organs were found in them.