Abstract
After various kinds of the dust collector were inspected and compared in order to observe radioactivity in the air, the electric dust collector was proved effective for the purpose.
Natural radioactivity in the air averages some 10-16C cm-3, which is mostly due to Radon daughter and Thoron daughter. The rel a tion between suction time and saturated time of natural radioactivity was studied.
Also is reported the diurnal variation of artificial radioactivity in the air from November 1954 to March 1956. Its activity reached some 10-7μc/l at maximum.
