The Results of Routine Observations of the Ionization and the Natural Radioactive Dust Concentration in the Atmosphere in Tokyo. (Preliminary Report)

Abstract

The ionizations byα-, β-, γ- rays and β-, γ- rays and the natural radioactive dust concentration in the atmosphere near the ground have been observed continuously at Tanashi, Tokyo, from April 1958. On fine days, the diurnal variation of the ionization by α-, β-, γ- rays is similar to that of the ionization by β-, γ-rays. The maximum value occurs at night (4-6h), and the minimum in the daytime (11-13 h). On cloudy and rainy days, the time variations are very irregular and the values are considerably larger than those on fine days. On fine days, the values of (β/γ)/(αβγ) are about 2-5 per cent, being large in the daytime and small at night, but the values on cloudy and rainy days are considerably smaller than those on fine days. According to the results of observations with an electrostatic precipitator the natural radioactive dust concentration is large at night and small in the daytime, and the diurnal variation being similar to that of ionization. But, the amplitude of the diurnal variation curve of the dust concentration collected with the electrostatic precipitator is remarkably larger than that of the ionization by β-, γ- rays measured with an ionization chamber.
The results of simultaneous observations mentioned above seem to be important for the researches on the natural radioactivity and on the frequency distribution of the particle size of the radioactive dusts in the atmosphere.
The abnormal increase of the ionization by α-, β-, γ- rays was found during the solar eclipse, 19 Apr., 1958. The maximum value occurred at the time of the maximum obscuration, and was over twice that on the other days.