The radioactive dusts floating in the sky over Japan at the altitude of between 10 and 12 km were collected by the use of an airborne sampler mounted on aircraft separately at the time when a nuclear test was carried out somewhere and at a normal time, and subjected to the measurement of radioactivity and ordinary chemical analysis to make a comparative study as to whether there exists any difference between the radioactive dusts collected at two different times.
As a result of this study, it was found that the density of radioactivity in the air at the time of a nuclear test was about 500 times as high as at a normal time, whereas the density of the dusts in the air was the same at about 10μg/m3 at both times and the component elements of the dusts were Si, Fe, Al, Mg, etc., with no much difference discovered.
