Estimation of ^<137>Cs Body Burden in Japanese II. The Biological Half-life

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The biological half-life of ^<137>Cs in the total body of human subjects was determined in 23 individuals of Japanese male adult in their normal works by measuring amount of ^<137>Cs in both their total body and daily urine in the same period. For the group, the value was determined by averaging the half-lives for individuals, by comparing the mean body burden and the mean daily urinary excretion, or by applying a curve fitting method to the body burden estimate. The biological half-life averaged 86 days, ranging from 50 to 161 days. The averages of the biological half-lives for the group were 83, 87 and 82 days in the different periods of observation. By the curve fitting method, 85 days was found for the group. The biological half-life for the individuals depended on both body weight and age, to a lesser extent, of the subjects. ICRP 2 gives the biological half-life of 70 days to Cs distributing in the total body. However, the value was derived based on very limited number of subjects from some limited area. A lot of factors like age, sex and ethnic group may result in a different biological half-life and even economic status may contribute to the biological half-life because of possible difference in food consumption in both quality and quantity. In fact, the available values of Cs biological half-life in the total body obtained thereafter indicated the rather wide distribution as indicated graphically later.
日本放射線影響学会の論文