The photos of the first millisecond of a nuclear detonation were taken using a rapatronic camera, which is capable of recording still images with exposure times as short as 10 nanoseconds. To put this into perspective, most modern cameras can take photos with exposure times of 1/8000 of a second, equal to 125 microseconds, meaning rapatronic cameras are up to 12,000 times faster than standard ones.
The photos were taken during the Tumbler-Snapper performed in Nevada circa 1952 from 7 miles away. In the first image, the fireball is about 20 m (66 ft) in diameter. The spikes at the bottom are known as the “rope trick” effect, and we can also observe a mottled surface.
The “Rope Trick” Effect
The “rope trick” is caused by the heating, rapid vaporization, and then expansion of guy wires (or specialized rope trick test cables) that extend from the shot cab, the housing at the top of the tower that contains the explosive device, to the ground.
A physicist named John Malik observed this effect when the rope was painted black, spike formation was enhanced, and if it was painted with reflective paint or wrapped in aluminium foil, no spikes were observed – thus confirming the hypothesis that it is the heating and vaporization of the rope, induced by exposure to high-intensity visible light radiation that causes the effect.
Because of the lack of guy wires, no “rope tricks” effects were observed in surface detonation tests, free-flying weapons tests, or underground tests.
Mottled Surface Explained
The reason for surface mottling is more complicated. Thermal x-rays emitted by the detonation process form a fireball around the bomb in the first microseconds after the explosion. The bomb is expanding inside the radiative fireball as a result of the heat generated by the nuclear reactions.
This generates a hydrodynamic shock wave that travels at supersonic speeds outward. This shock front reaches and then passes the radiative fireball after a brief duration. The shock front is roughly twice its size at the point of the explosion depicted in the shot above.