FORMATION OF RADIOACTIVE PARTICLES 4 At the time of detonation of a nuclear weapon, about 60 different isotopes are formed, representing some 35 elements. Most of these give rise to decay chains consisting of several isotopes so that there may be 170 isotopes produced eventually. ° In terms of activity, a one megaton detonation (1,000,000 tons) TNT equivalent energy produced by fission of atoms will result in about 300,000 megacuries of radioactivity, measured one hour after the burst. In addition there may be present induced radioactive isotopes resulting from the reaction of neutrons released at the time of detonation, with natural materials such as soil and water. fA fusion reaction produces no radioactive substances directly but may cause induced activity because of its release of neutrons./ The total radioactivity of the products of a fission reaction will greatly exceed that of the activity induced in the soil or water. In the case where the fireball clears the ground, there will be a relatively small percentage of the total fission product activity deposited around ground zero and the neutron induced activity probably will be much greater. However, none of the neutron-induced isotopes that might be produced in appreciable quantities have long half-lives. Shortly after a nuclear burst, some of the radioisotopes combine with oxygen to form negative radicals while the halogens form halides which combine with the strongly electropositive elements to form compounds. The noble gases such as~radiokrypton and radioxeon ~~ if