Cloud radioactivity intensity

Figure 2. Typical cloud radioactivity intensity contours 15 minutes after burst. Intensity is in arbitrary units...

The detailed structure of the radioactive cloud after stabilization has occurred (within 10 minutes) has not been studied extensively. Figure 2 shows some relative radiation intensity data obtained by rockets following the Zuni explosion (3.5-megatons, coral island surface). The data pertain to the situation 15 minutes after the explosion. The evidences of a toroidal structure are still marked. Note that the bulk of the radioactivity is in the core of the cloud and that the distribution, either horizontally or vertically, is far from uniform. The aircraft samples on Zuni were collected at 41 kft., well below the core of concentration as found at 15 minutes. Since only the lower fringes of the nuclear cloud were penetrated, analyses probably do not represent fairly the nuclear cloud as it existed at the time of sampling. 

One of the causes of aerosol increase in the atmosphere is the radioactive burst in the epicenter of underground nuclear explosions. If after an explosion, the aerosol cloud gets into the zone of jet flow, it will settle down or rise up depending on the leg it encountered (anticyclone or cyclone). The higher the wind velocity in the jet is, the higher the layer of maximum values of aerosol concentrations is located. The upward aerosol transfer on a cyclone leg is more intensive than the downward transfer on an anti-cyclone leg, as the ascending vertical velocities are more powerful than the descending ones. 

The intense heat lofted this cloud of lethal materials high above the surface, forming a cloud more than 120 miles long and 30 miles wide. As the cloud cooled, much of the radioactive contents returned to earth as a powdery shroud. The fallout particles clung to the skin of people exposed to the powdery rain. The fallout was inhaled as people breathed and ingested when they ate contaminated food. Particles in the environment and on the skin of the people emitted gamma rays, which penetrated their bodies, and beta rays, which burned their skin. 

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