What elements make a mushroom cloud?

Answer 1

Particles from air bursts are smaller than 10-25 micrometers, usually in submicrometer range. They are composed mostly of iron oxides, with smaller proportion of aluminum oxides, and uranium and plutonium oxides. The particles larger than 1-2 micrometer are very spherical, corresponding to vaporized material condensing into droplets and then solidifying. The radioactivity is evenly distributed through the particle volume, making total activity of the particles linearly dependent on particle volume. About 80% of activity is present in more volatile elements, which condense only after the fireball cools to considerable degree. For example, strontium-90 will have less time to condense and coalesce into larger particles, resulting in greater degree of mixing in the volume of air and smaller particles.