l hour after the burst would be expected to be 0.1 R/hr after ff hours and 0.01 R/hr after 49 hours. This rule seems to be valid for abdut 6 months following an explosion, after which the obServed decay is som than that predicted by this relationship. The activation pro general, decay at a faster rate than the fission products. Fission products and the activation products, along with uranium or plutonium from the device, are the components of t fissioned radioactive material in the fallout cloud, and this cloud is the primary tential exposure to residual radiation. In a nuclear airburst in which the central core of intens terial, or fireball, does not touch the surface, the bomb res ing the fission products, the activation products resulting f interaction with device materials, and unfissioned uranium an nium) are vaporized. These vapors condense as the fireball r cools, and the particles formed by the condensation are small like. They are carried up with the cloud to the altitude at rise stops, usually called the cloud stabilization altitude. of this material then depends on the winds and weather. If tlle burst size is small, the cloud stabilization altitude will be in the lowdr atmosphere and the material will act like dust and return to the Earth's|surface in a matter of weeks. Essentially all debris from bursts with yie lent to kilotons of TNT will be down within 2 months (Referen areas in which this fallout material will be deposited will agfpear on maps as bands following the wind's direction. Larger bursts (yields equivalent to megatons of TNT) will have cloud stabilization altitudes ig’ the strato- sphere (above about 10 miles [16 km] in the tropics); the radgoactive material from such altitudes will not return to Earth for many its distribution will be much wider. @onths and Thus, airbursts contribgte little potential for radiation exposure to personnel at the testing grea, although there may be some residual and short-lived radiation coming fom activated surface materials under the burst if the burst altitude is sufficiently low for neutrons to reach the surface. 29