Following a single subcutaneous injection of ⁹⁵Zr-⁹⁵Nb to young and adult rats, the concentrations of the nuclides in several organs were studied during the observation period of 63 days. The concentrations in the tibia, lungs, liver, kidneys and spleen of the young rats were much higher than those in the adult rats. The concentration in the tibia, among these organs was the highest both in the youngs and in the adults. Moreover, in the tibia, ⁹⁵Zr-⁹⁵Nb retained longer than in other organs. So, if ⁹⁵Zr-⁹⁵Nb invade into the body fluid through any route of entry, the radioactive nuclides deposit mainly in the bone and may have possibility to cause radiation injury to the bone marrow.

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Quantitative distribution pattern of cesium-137 and strontium-90 was determined in a forest area after preliminary studies in different sites. Both radionuclides were found in the fallen leaves in the highest concentration and this fact can be reasonably explained by that the fall-out rates were the highest three years before this observation. About 80 and 63% of the total deposition respectively of cesium-137 and strontium -90 were found in the upper 5 cm layer of soil, 18 and 23% in the vegetation, of which 11.4 and 10.7% in the fallen leaves. Root absorption of strontium-90 by pine tree and shrub was considered at least two times higher than that of cesium-137.

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Cysteamine afforded marked protection against the effects of X-irradiation on both dose-dependent accumulation of fructose-1, 6-diphosphate and ATP depletion to an approximately equivalent extent, giving the dose-reduction factor of about 2. This was considered as support for the view that both phenomena are closely related and arose from a common event. Little protection was afforded under the same conditions against irradiation-induced accumulation of pyruvate and lactate in the lower dose range. Possible mechanisms underlying these phenomena are discussed.

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In adults of the small fresh water teleost, Oryzias latipes, it was shown that the curve showing the relationship between the survival time after X-irradiation and the dose applied is similar in shape to those reported for laboratary rodents : Small doses of X-rays did not exert acute lethal effect on the fish, while very large doses killed the irradiated fish instantaneously. Between these extremes, some dose ranges were distinguishable from others by the difference in effects on the post-irradiation survival time. The survival times of adult fish irradiated with various doses within the range from 4 kR to 32 kR were approximately the same. When the fish were irradiated during early embryonic stages, such “dose-independent range” as demonstrated in adult, was not demonstrated and dose-survival time relationship curves for the embryos were simpler in shape than those for adults of the same species. A possible explanation for the change in the relationship during embryonic development is discussed.

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An experiment was made in order to confirm the possibility to determine the age of nuclear debris by measuring the activity ratio of ⁹⁵Zr to ⁹⁵Nb. The photopeaks due to ⁹⁵Zr 757 kev γ-rays and ⁹⁵Nb 766 kev γ-rays can be clearly resolved from each other by a Ge (Li) detector with high resolution. The agreement between calculation and experiment was fairly good. This method can be applied with appreciable accuracy for the age determination of nuclear debris in an age range from about 15 to 100 days. In the case of debris samples which are much depleted in volatile nuclides, such as highly radioactive fallout particles from an air burst, the youngest age that can be determined by this method is appreciably less than 15 days.

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Experiments were conducted to determine the LD_50/30 of Wistar strain male rats, aged 72 to 112 days, bred in National Institute of Radiological Sciences. The animals were irradiated at eight exposure levels between 600 and 90O R of X-rays at rate of 23.5 R/min. Probit analysis of mortality data yielded an LD_50/30 of 761.6±31.8 R. The body weight of the animals was decreased gradually after irradiation, reaching a minimum value at 4th day after the exposure. The body weight of 30-day survivors shows the second minimum value at 18-21 st day after irradiation.

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The ionizations by the beta and gamma-radiations near the ground were measured in and around Nagoya during the last four years (1963-1966). Although the ionization by the beta-radiation decreased gradually from 1963 through 1966, that by the gamma-radiation did not decrease remarkably. Therefore, the contribution of the beta-radiation to the ionization of the air exceeded that of the gamma-radiation from 1963 through 1964, while the latter exceeded the former in 1966.
In general, the ionization by the beta-radiation from the ground surface covered with the grass exceeded that from the ground covered with no grass because of the fallout radioactivity accumulated in the leaves and roots of the grass.

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The results of the measurements of ionization due to the beta and gamma-radiations near the ground surface from 1967 through 1969 are reported, and are discussed comparing with those obtained from 1963 through 1966. The ionization due to the beta-radiation decreased gradually, and the mean value for this period is about I J at one meter above the ground surface, and that by the gamma-radiation (including the cosmic rays) is almost constant, i. e., 5-6 J.
In January 1967, sudden increase of the ionization due to the fallout radioactivity caused by the 5th Chinese nuclear explosion test was observed. ¹³⁷Cs, ⁹⁰Sr+⁹⁰Y, ¹⁰⁶Ru, and ¹⁴⁴Ce were detected from the grass and soil samples taken on the campus of this university in 1964. ¹⁴⁴Ce, ¹⁴⁰La, ⁹⁵Zr, ¹³²I, and ¹³²Te were also detected from the fallout particles caused by the 3rd Chinese nuclear explosion test on May 9, 1966.

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Activation of myosin-ATPase by irradiated histidine was studied. The kinetic constant and the optimum pH for the activated enzyme were found to be different from those of non-activated enzyme. An activating agent was separated from the irradiated histidine solution, through a column chromatography on ion-exchange resin. From its chemical properties and spectral characteristics, this was first assumed to be hydroxyhistidine. However, a peroxide which is more effective in activating the enzyme was also obtained from histidine on irradiation. Oxygen is needed for the production of this peroxide. Based on the studies of its sulfhydryl reactivity and heat stability, it was concluded that the peroxide concerned was not hydrogen peroxide, but presumably hydroxyhydroperoxide of histidine. From comparative studies on the activating effect on myosin of irradiated histidine and other sulfhydryl reagents, it was confirmed that irradiated histidine attacks a sulfhydryl group which is concerned with the conformation of myosin molecules, leading to an activation of myosin-ATPase.

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It has been already shown that ionizing radiation brings about the enhancement of phosphofructokinase reaction in rat thymocytes and a consequent accumulation of fructose-1, 6-diphosphate. Protein synthesis inhibitor, such as cycloheximide was shown to have no effect on this accumulation. Explanation of fructose-1, 6-diphosphate accumulation in terms of the stimulated de novo synthesis of phosphofructokinase could be, therefore, ruled out.

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