It is now well estadlisnad that fallout rarticl2s are re~ moved from this lower layer of the atmospher2 in the first month or so3 ther2fore, the tropcspheric fallout stays airborne at most a matter of a month or two before being deposited. Of course, in this time, it will in general move zreat distances, possibly even clear around the e2arth; but, in Zaneral, it stays in the general latitud? in which the exriosion occurred. So, the second type of fallout, the troposzneric world-wide fallout, produces a band of raiioactivity in the general latitude of the firing site. Th2 fraction of the fallout which falls in this category depends mainly on the bomb yield and the coniitions of firinz. 4 bomb which is fired on the ground produces a maximum of local fallout, naturally leaving less for the world-wide fallout of either the tropospheric or stratospheric variety. Tha bomb yrend determines the division of the world-wide fallout bdetwe the two kinds of worldwide fallout. 4 general rough rule is that a one mesaton bomb will produce clouis which cush inte the higher layer of the atmosvhere, the stratosphere, before disseminating and thet the clouds from dombds of less than one megaton wiil tand to stay mainly in the trovopsnere. Thus, we s22 that 2a 590 xiloton wespon fired so its fireball did not touch the ground would be expected te put the major part of its radioactivity in a band stretching clear around the world in the general latitude of the firing site. The distribution of the activity we ld be worldwide ani vould be completed within the first month or Simils“rly, the sam2 bomb fired in coneact with thea two. 2artn with orainery soil would have a large fraction-- somatnins like &O percent--of its fallout deposited within the first faw hours within a few hundred tiles test Site and the rest of the material would be i ropospnsric world-wide fallout patt arth in the same Zensral lat . (it time. > ch Wwlw SH wv es fo [tt 2 od eth e oO to uw Cc w if he third type of fallout is the 5s sllovt. weapons of yields of on thrust their radicactive clouds int n and the material which doss nct fall cf its ownwe within the first few nours is then very largely borne in the stratosphere for great lenzths of An average time seems to be about 10 years or somewhat less. They produce a small amount of tropospheric world fallout elso, presumably due to a small (more) (24