Monthly mean concentration of radon daughters is estimated assuming the radioactive equilibrium by use of the survey data of radioactivity obtained at five stations in Japan for the past ten years. An overall mean is 90×10^-18 curie per cm³ of the air. Causes of errors accompanying the measurement and estimation are discussed.

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The changes with time of the dietary levels of fallout ⁹⁶Sr, ¹³⁷Cs and ⁹⁵Zr-⁹⁵Nb at Tokai-mura, Ibaraki Pref., Japan (36°36'N, 140°27'E) were determined during the time from 1962 to 1965. During these four years total diets were collected for thirteen periods, each period of time consisting of 5 consecutive days. The mean daily intakes for 5 days were determined. On the other hand, surface air dust was continuously collected and mean monthly concentration was measured.
The levels of these nuclides in the diets and the air were minimum in the summer of 1962. The air concentration of ⁹⁵Zr-⁹⁵Nb reached the maximum in the spring of 1963. However, it decayed thereafter rapidly. This variation of ⁹⁵Zr-⁹⁵Nb with time was similar to that of the dietary level. The level of ¹³⁷Cs in the diet increased since the summer of 1962, reaching about 10 times higher level in 1964. The dietary level of ⁹⁰Sr also increased but it was not so conspicuous as ¹³⁷Cs. The dietary level of ⁹⁰Sr and ¹³⁷Cs changed in parallel to concentrations in the air, although the latter fluctuated more intensely than the former.

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Reaults of quantitative studies of radiosensitivity and radiolytic mechanisms of methionine in aqueous solution exposed to gamma-irradiation are presented. The products of methionine, methionine sulfoxide, methionine sulfone, α-amino-n-butyric acid, homoserine, homocysteic acid and homocystine, which were irradiated separately under identical conditions were studied using an amino acid analyzer. The probable pathways on the radiation decomposition of methionine are discussed.

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Two single doses of coupled radioisotopes of ¹³²Cs-⁸⁶Rb and ¹³²Cs-⁴²K were orally administered to a human subject. Body retention, urinary and fecal excretions as well as the plasma and erythrocytes contents of radioisotopes were determined. The proportion of urinary to fecal excretion was found different in cesium and rubidium, the urinary excretion being 85.3% of the total in the former and only 68.1% in the latter. Loss of cesium in the sweat amounted to 1.5 and 3.5% of the total excretion for the first two days. Uptake by the plasma of oral dose was rapid and the whole blood content reached max. 11.4% of the dose of cesium at 1 hour, while 2.9 and 2.4% respectively of rubidium and potassium was reached. The levels in the erythrocytes seemed to grow at a slower rate in cesium than in the other alkali elements. The different feature of blood metabolism found in the alkali elements was interpreted by the slow rate of clearance of ingested cesium from blood. Daily fluctuations of fall-out ¹³⁷Cs in blood and the errors involved in the assessment of the total body burden of ¹³⁷Cs by blood analysis were also discussed.

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