remain in the atomic state until they decay to a daughter isotope which can form an oxide or halide. With the rapid cooling of the fireball, there is condensation of the isotopes and inert materials. ¥ In the case of an air burst there will be available only small quantities of relatively fine particles of dust in the air and debris a from the bomb casing to act as a transport vehicle for the radioisotopes. When the fireball intersects the ground the intense heat melts or vaporizes large quantities of soil and transports them aloft to act as carriers for the condensing radioisotopes. A characteristic toroidal motion sweeps this debris in and around the fireball where the melting temperature is reached and the particles come in contact with the fission products still in gaseous form. Subsequent cooling results in the radioactive isotopes becoming associated within and on the surface of the particles. It has been estimated that from 50 to 90 percent of these particles are between 50 and 1,000 microns in diameter. Of these, probably less than half of the larger particles falling out near the site of the detonation will possess any activity, since most particles will not reach sufficiently high temperatures to incorporate the radioactive materials, and dry, relatively cool, soil is a poor scavenger. The high yield weapon detonated at the Pacific Proving Ground in the fall of 1952 resulted in a crater in the coral nearly a mile in diameter and 175 feet deep. Although a minor factor in the crater production might have been the compression of the coral by the blast, probably more than a hundred million tons of material were dis- lodged and thrown into the air. The exact results might not be ; i; a —