In this case,.the anomelous oscillation of the atmospheric pressure was not observed. This might indicate that it is rather an experiment of a large atomic bomb rather than the real hydrogen bomb, The half-life of the radioactivity observed after September 19 is short, being of the order of 7 to 10 days. Of course, this simply means that the explosion occurred very recently and not that the Russian bomb is made of radioactive substance of shorter half-lives, By the way, as is seen in Fig, 6, the air mass to the north of Japan receded northwards around September 25 and the air flowed to Japan from the south, It is interesting to notice that the amount of radioactivity carried by the rain decreased quite appreciably during this period, The result of chemical analysis shows that this rein involves the artificial radioactivity consisting of nearly the same elements as that made in Bikini. As mentioned before, this case is contrasted to the Bikini case in the sense that the radicactivity appeared only in the Tohoku district and the Japan sea coast and not on the Pacific coast, On the basis of the above informetion, it was concluded that the radioactive rain reported after. September 19 was produced in Russia. Department of Energy : Histcrian’s Oifice Dangerous Radioactive Snow haACKIVES It mzy be a troublesome problem if the Russian-mede radioactive rain turns into snow and fells on the Tohoku and Hoknriku districts which ere the pleces suffering ennually from heavy snowfall. It is not known how long the Russian redioactivity will renain to stain the rain or snow, but in view of the Bikini cese, it may be expected that the radioactive rain of several hundred cpm/1 will be observed for a considerable period. It is well known in the cese of natural redicactivity that the snow is a better collector of radicactive substances in the etmosphere than the rein. Tnis is due to the fect that the sncewfleke gces down slower in the eir than the raindrop. Thus, when the conitezinetion of the air is of the sere order, the snow will become more relicactive than the rain, Usuelly 60 to 70% of the rein weter escapes Girectly into the river. On the otner hand the snow wili ste} on the ground for 42 long tine and heave a larger probabiiity to sink inte the scil. Ynovgr it is very urtikecty, people in the snowy districts migni happen to be exncsed to the radicaectivity ever é long period, if the snow fails with stireng reecicacvivity. There is also @ possibility thai the water of rivers become redicactive when the snow melts and contaminates the water for drink eswell es the weiter in shallow bays elong the coasts resviting in é canage to the sea products. The nost dangerous of ell is, however, th cese where the snow itself is used for crinking and cooxing which is likely to occur in the moun om ilecle in such ceses will te to metncc Re ave The only practicalVV ometrnen Gistricts, ols + t2in ad ‘EY