One Millisecond After a Nuclear Explosion

This picture of a nuclear explosion in just one millisecond after detonation was made on the ground in Nevada 1952, by the Rapatronic camera model Edgerton with exposure time of 3 microseconds.

At this stage of the detonation the surface of the fireball has a temperature of 20,000 degrees (it's three times hotter than the surface of the sun). At such temperatures the amount of thermal radiation given off is so enormous, so anything it touches is vaporized ahead of the expanding fireball.

The three spikes in this image result from the guide wires supporting the tower on which the bomb was located absorbing enough heat to turn into light emitting plasma. Because thermal radiation travels faster than the fireball, the spikes extend out ahead of it.

One might expect an explosive fireball to expand in a perfect sphere. Actually, variations in the density of the bomb's surrounding case create the mottlings and and complex shapes in many of these images.

A little bit later, we can see the shockwave propagating ahead of the fireball. Under the balloon, you can see how the blast wave is reflected from the surface of the desert and rises up.

Some other bomb-facts:

• During the early years of nuclear research, the main effort was in creating larger and more powerful bombs, many of which were rated at several tens of megatons. However, military experts quickly discovered that since the energy from a detonation expands in a sphere, much of the energy is wasted at high altitudes. The optimum size, in terms of the most destructive power from the smallest amount of fissionable material, comes from bombs in the 100-kilotons class.
• The average US bomb measures 250 kilotons.
• The average Russian bomb measures 400 kilotons
• A nuclear detonation occurs when enough fissionable material (called the critical mass) is brought together quickly enough to cause a runaway chain reaction. For uranium 235 this is around 22 pounds.
• Nuclear fuel is unbelievably energy dense. The volume of plutonium used in the Nagasaki bomb was the size of a softball. Even more amazing is that the 21 kiloton yield reflects a very inefficient use (a few percent) of the total energy potential of the plutonium.
• Nuclear explosions are possible from smaller amounts of fissionable material by using the extremely high pressure of a surrounding chemical explosion to compress fissionable material to such a high density that a runaway chain reaction can be sustained.
• The largest nuclear weapon ever exploded was Russia's "super-bomb," rated at 57 megatons. Detonated in 1961, it was largely for political purposes because at the time the Soviet Union had no airplane or missile that could carry the 27 ton bomb over any great distance.