The ionization of the air due to beta- and gamma-radiations near the ground. (II).

The results of the measurements of ionization due to the beta and gamma-radiations near the ground surface from 1967 through 1969 are reported, and are discussed comparing with those obtained from 1963 through 1966. The ionization due to the beta-radiation decreased gradu ally, and the mean value for this period is about I J at one meter above the ground surface, and that by the gamma-radiation (including the cosmic rays) is almost constant, a. e., 5-6 J. In January 1967, sudden increase of the ionization due to the fallout radioactivity caused by the 5th Chinese nuclear explosion test was observ ed. 13 7Cs, 90Sr+90Y, 106Ru, and 144Ce were detected from the grass and soil samples taken on the campus of this university in 1964. 144Ce, 140La, 95Zr, 132I, and 132Te were also detected from the fallout particles caused by the 3rd Chinese nuclear explosion test on May 9, 1966.