Vertical penetration of Sr-90 and Cs-137 down to 5, 000m depth was confirmed in the western North Pacific. Surface values of these radionuclides range from 0.6 to 3.1 μμC/L for Sr-90 and from 0.8 to 4.8 μμC/L for Cs-137, while at 5, 000m depth both nuclides of about 0.1 μμC/L were determined. From the vertical variation in the concentration of radio-nuclides, the vertical diffusion coefficient from 200 m to 4, 000m depth was calculated and the value of 200 was obtained. Time required to attain practically a homogeneous vertical distribution of substances which is put in the western part of the north Pacific Ocean would be a few hundred years.

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It has been pointed out that Sr-90 deposition is much greater in the temperate zone than in the tropical or polar zones with respect to the same amount of precipitation. This means that there is a difference in the air-borne activity between zones. The concentrated accumulation of radioactive debris in the temperate zone seems to be related to the meteorological conditions in the upper troposphere. In the temperate region between 30°N to 60°N, troughs at 500 mb and above are often observed while few troughs appears in the polar and tropical regions. The radioactive dusts may be carried down to the lower troposphere owing to the subsidence of the air behind troughs and north of jet streams. This may accelerates the deposition of radioactive dust on the middle latitude.

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For evaluating the yearly variation of C¹⁴ concentration in diet, radioactivities of C¹⁴ in ethanol were measured by liquid scintillation counting. Samples used were ethanol produced by fermentation from various vegetables and their data of photosynthesis ranged from 1949 to 1960. After purified from alcoholic beverage or ethanol of chemical grade, they were mixed into toluene scintillator and were counted by a low level liquid scintillation counter.
Increase in C¹⁴ concentration, which was caused by the artificial production of C¹⁴ from nuclear test explosions, was remarkable from 1955 and the rate of increase was 4%/ per year.

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Measurements were made of potassium, rubidium and cesium in a variety of Japanese diet samples to know the fate of these elements in food chain.
Each component of the diet contributes potassium evenly to the diet, however, almost a half of cesium is estimated to be contributed by meat, eggs and milk products. Thus, the daily intake of cesium varies greatly depending on the dietary intake of this component. The daily intake by the Japanese adults as a whole is estimated as 1.4 g of potassium, 1.5 mg of rubidium and 0.01 mg of cesium per person.
The biological half-lives are estimated as 54, 140 and 76 days, respectively, for potassium, rubidium and cesium on the basis of the balance between the human body and diet assuming a single exponential function of excretion.

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The influence of stable carriers on the deposition of radioactive strontium in the bone was investigated. The deposition of calcium-45 or strontium-89 was observed to depend on the solubilities of their salts at the time of administration. Therefore, the concentrations of radioactive strontium in bone calcium were calculated on the basis of calcium content in soluble fraction of foods. The interference of calcium carrier on the deposition of strontium-89 in rats femurs could be recognized only under the calcium deficient condition. Using tissue culture of chick embryonic bone, the uptake of strontium-89 was evidently depressed by the addition of strontium carrier in the medium rather than by calcium carrier.

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Stuies on the detection of the long-lived radioactive fallout due to the A-bomb explosion in Nagasaki were carried out in Nishiyama district in 1959. Mud collected near the Nishiyama water reservoir was treated chemically. The radioactivity of the sample No. 10 was 20 times as much as the natural background, and its beta and gamma components of the sample was also measured.

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Measurements have been made of the cesium-137 content in human musle, total diet and cereals collected in Japan during the period from February 1960 to May 1962.
The simple methods of evaluation of mean levels in the human body are proposed which are based on the distribution studies on the common cesium irrespectively of potassium concentration or the cesium unit.
The total body burden was estimated as 3.2-4.0 mμc for the period from August 1960 to January 1962 and it rose up to 7.6 mμc in March 1962 in correspondence with the increased fallout deposition rate in Autumn 1961. The daily intake of cesium-137 by Japanese people was 29 μμc, on average, for the period from August 1960 to August 1961 and increased to 50 μμc in February 1962.
The contribution of cesium-137 by cereals to the total intake was estimated as approximately 40% for the period from November 1960 to November 1961 and it decreased to 32% in February 1962. The relative decrease was attributed to the increase in the daily intake, probably other than cereal, through leafy vegetables.

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