The radioactive intensity of the rain water which fell on Nagano-District from May 21,1954, to October 31,1956, was measured with the Radiation Counter (Model 32), manufactured at the Scientific Research Institute, LTD., Tokyo, Japan. In order that the measurements were to be carried out accurately, the Geiger-Muller counter tubes used in the measurements had been examined carefully and their characteristics were studied in conformity with the curves representing the relation between the applied voltage and counts per minute of the radiation-ray. The results of the measurements show that the radioactive intensity of the rain water in Nagano-District considerably increased at certain periods of time after the explosion experiments on the nuclear-missiles were made on the coral-reeves in the South Pacific Ocean by U. S. A. and in Siberia or its vicinity by U. S. S. R.. From the manner of the radioactive decay, it can be concluded that the intensely increased radioactivity was not due to the natural source, but to the artificial one. This paper is attached by numerical data on the measurements of the radioactive intensity of the rain water in Nagano-District.
信州大学工学部紀要 6: 157-170 (1956)
信州大学工学部紀要 6 157-170, 1956-12-25