- 44 fallout 18 worldwide; in smaller detonations, the cloud remains in the troposphere and dgstribution of fallout is limited. The point of division between a large and a small detonation is about 200 KT (energy released equivalent to 200,000 tons of TNT). For all detonations there is a large amount of local fallout within a few hundred miles of ground zero, ation. occurring within a day or two of the deton- In the Bikini-Eniwetok area the radioactivity in the local fallout resides on particles of Nacl, cao, Ca(OH)o and CaCOz made by the great heat of the fireball acting on the coral of the islands and the sea floor. over other types of soil, For detonations different compounds would be formed by the fireball and would occur in the fallout. In the Atlantic Ocean fallout has been either tropospheric or stratospheric and measurable amounts are detectable if special techniques and sensitive counting methods are used. In the Pacific Ocean, local fallout in the vicinity of the test sites of the United States and the United Kingdom has contributed by far the greatest amount of radioactivity to the ocean. The movement of radioac- tivity from the U. S. test site at Bikini and Eniwetok Atolls has been estimated and the amount of radioactivity in the water has been measured by both United States and