of whether a surface or air burst, the fireball will spread upward from 100 to 300 miles per hour at the beginning, and slowing as it approaches peak altitude, If the explosion occurred on the ground, the fireball will suck up with it great auantities of soil and incinerated materials, carrying the lighter ones to its highest altitude, Local fallout of this material will be heavy and only the lightest particles will ascend to thousands of feet. If, however, an air burst, the heat and shock waves will be maximized, but little material drawn up into the cloud with the fireball; consequently, there will be little local fallout. out during the gaseous firehalls' Great amounts of radioactivity are sent formation and as it rises. However, if it is an air shot ,little radioactivity will be dispersed locally since little material has been uplifted, and since the majority of the some 200 radioactive products are so short-lived that many of them have gone throughone or two half-lives before the cloud has peaked. Essentially, in an air burst the main radioactive elements are from the material itself, water vapor in the air, and the metal bomb parts themselves, which have become mixed with the fireball. A nominal 20 kilotron (20,000 tons of TNT) burst will rise to about 20 or 30,000 feet, A one megaton bomb (1 million tons of TNT) will rise within 10 minutes to a height of roughly 100,000 feet, If it was a ground burst, it will have pulled up with it tremendous amounts of matter and made it radioactive. The cap of the cloud will have poked itself into the stratosphere where high winds will begin dispersing it worldwide, The rest of the cloud column will be torn about by lower winds which will carry the radioactive debris with it. The heavier particles fall out first, and lighter ones fall hack down later upon the earth below, in a design created by the wind, a? 12