returnito earth, during the first few hcurs, of the larger -particlas: from the fireball; these include nesidues from the soil and structures which are swept into the fiteball and) either*wholly or partially vaporized. — The fraction cf the total debris which falls out locally depends: very much on the conditions of firing. The Since the nuclear debris remains in the stratosphere for these long times, relatively complete mixing within the stratosphere should be obtained and one expects that the fallout from:this seurce should be essentially wiiform over tne entire world. After passing through the trgpopatiss into the troposphere it will be rained out rather quickly. Besause of the long residence time in the air,'this type of fallout_is not a serious gamma ray hazard since Cesium-137 (C5137), the principal gamma emitter jeft after one year is relatively harm- less. /: Two years ago, it was estimated that there were about 24 megatons of fission products stored in the stratosphereiccrresponding (iff it were all de- 7 posited uniformly on thaiearth) to:about 12 millicuries of Sx90 pev square mile ‘tand about 3137. ’ i — (more) ' the same amount of aes iisesishsaitiase . sere - cep ~ ee ‘ sas , named tas wal : lyn kts. « fae . Mar sane Thess TR, . Ee6 OlaeRaslSma ainbiel o NEta acnkeinatdisiceis residence time of seven years (or less). . >. few hours is than largaly borne ingthe stratosphere for | great Jengths of’ time. An averageztime seems to be about ten years or somewhat less, corresponds ng to a half .- ' which does not fsll of its own weight within the first . Wigh-yleld weapons thrust their yadioactive clouds into the stratosphere and the material a « atti ee ; wget world-wide fallout. | aernsee ' 7 hm on the:size of the explgsion and the conditions of firing. The third typeof falloutfis stratospheric 7 plosiontand so leads toa band of ‘radioactivity at the general lativude:of the#firing site. The fraction of the fallout. which falls‘:in tais category depends mainly Boece flag! ok — :. wirie , Although this fallout will in general move distances,:it stays near the’ latitude of the ex- os great = troposphere. 2 seconiitype, tropospheric world-wide fallout, is the - material which though not coarse enough to fall of its own weight in the firse:few hours “is nevertheless left in theflower layer of the atmosphere, that is the