For surface bursts of high (million ton range) yield from 50-80 percent of the radioactive debris is deposited as "early faliout:, i.e. within 24 hours. Air bursts - where the fireball does not approach the surface - create little, if any, local fallout. Table 2 tabulates some of the key data on estimated nuclear energy yields from all past nuclear weapons tests. rei: jres The total energy release is of interest in estimating the amount of carbon-14 produced. it is assumed that the carbon-14 is distributed more or less uniformly around the world. Of the total energy release of 511 million tons equivalent of INT about 70 percent resulted from USSR tests. un Table 2 also shows that tons of the fission products from 161 million tons was scattered globally. Approximately two-thirds of this amount originated from USSR tests. It will, however, account for about three-quarters of the long-term fallout in the United States because of meteorological] factors - there will be more deposition in the North Temperate Zone from a nuclear detonation in the lower atmosphere at a northerly latitude than from the same shot at an equatorial site. Atmospheric tests at the Nevada Test Site have contributed very little to the deposition of long-lived radioisotopes but at times have been the source of relatively high amounts of short-lived iodine-131 in the local environment. At the time of a nuclear detonation something like 200 different radioactive substances are formed by fission and additional ones by In