Studies on the radioactive contamination of fruit trees by fission products, 5

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.