From 1961 through 1971, the distribution of fallout 137Cs in the skin, juice and residue part of the mature fruit of Satsuma orange trees grown on soils under clean, mulch and sod systems of soil management was investigated to compare its annual change with that of 90Sr. Due to a great dependency on the fallout rate the level of this nuclide in each of the fruit parts showed a high concentration during the period of heavy fallout deposition followed by a sharp decrease. After this, a slow exponential decrease was observed with almost the same half-time as that of the replaceable 137Cs content in soil during the period of very little fallout deposition. The ratio of the 137Cs contribution due to direct (surface) absorption, root absorption and translocation from leaves was 95:4:1 for skin, 44:45:11 for juice and 34:53:13 for residue in 1963 with heavy fallout deposition. The ratio of 137Cs/K in plant tissues to replaceable 137Cs/K in soil and the ratio of 137Cs to 90Sr in plant tissues were also discussed.
Tritium content in air and urine of workers was measured during and after the handling of about 30Ci tritium. Tritium content in environmental samples such as air and air-condensed water collected by a cold trap method was determined using a tritium monitor or a liquid scintillation counter. Internal radiation dose was estimated for workers by the analysis of their urine. The tritium concentration in air was about 10-9μCi/cm3 at the beginning of work, whereas the maximum value was observed during the working period as 2.6×10-4μCi/cm3 in hood, 1.3×10-6μCi/cm3 in laboratory and 1.8×10-7μCi/cm3 in corridor. The daily urinary excretion of tritium was represented approximately by a single exponential function with the effective half-lives of 14 days and 12 days for two workers, and their internal radiation dose was estimated as 12 mrem and 7.1 mrem respectively.
The ICRP Publication 14 contains two reports made by two Task Groups to Committee I. The first report is concerned with the spatial distribution of dose. In this report, many problems related to the basic concepts of radiation protection and inconsistency of the currently recommended dose limit are discussed. A scheme of dose limit for non-uniform exposure based on the risk estimate is presented tentatively. The second report is concerned with the relative radiosensitivity of different tissues and organs. In this report, risks of differnt kinds of biological damages by radiation are reviewed fully. A formal scheme for deriving dose limit for partial exposure of the body is presented. And, according to the data obtained from exposed populations, numerical values for dose limit to tumour induction are derived as an example for discussion. At present, the effect of radiation is not clear sufficiently, but it is suggested that the dose limit specified by ICRP for exposure of part of the body other than the lens and the gonads should be revised. In the present paper, the formal scheme for deriving dose limit and the example for the numerical derivation of dose limit are introduced somewhat in detail.