A flash of light, then an explosion
“Now I am become Death, the destroyer of worlds.” Nuclear scientist J. Robert Oppenheimer recalled this line from the ancient Hindu text the Bhagavad-Gita after witnessing the flash of light and massive destructive power of the world’s first A-bomb test, known as Trinity, on July 16, 1945. The blast produced a force equivalent to about 19,000 tons of TNT and signaled the opening of the atomic era.
Nicknamed “The Gadget” lest spies discover information referring to it as a bomb, the device was assembled on the top of a 100-foot tower and had an implosion-type design. This is how it worked:
THE TEST SITE
After considering locations in California, Texas and Colorado, the Army chose an isolated section of the White Sands Proving Ground in New Mexico.
At ground zero, the radiation was upwards of 75 roentgens for the first hour. Over time, the cloud of particles at the Trinity test site, which were radioactive, dissipated and lost most of its radioactive properties.
The explosion took place at 5:29 a.m. The heat of the blast was 10,000 times greater than is found on the surface of the sun, and the light was so intense that it could be seen from 180 miles away.
The explosion left a green, glassy residue on the desert floor. The sand reached temperatures above 2,678 degrees and melted.
THE FIRST 10 SECONDS
According to the official evaluation of the test, Trinity delivered a yield of about 19 kilotons of TNT, similar to the bomb detonated on the Japanese city of Hiroshima.
Trinity created an intensely hot and bright fireball that emitted thermal radiation capable of causing skin burns and igniting flammable material at a considerable distance. After the explosion, a destructive shock wave moved rapidly away from the fireball.
The primary blast wave struck the ground, creating another blast wave by reflection. The two fused to form a single wave called a Mach front.
Trinity’s fireball diminished in brightness, but it was still very hot and rising at a rapid rate, causing air to be drawn inward and upward, somewhat similar to the updraft of a chimney. This produced strong air currents, called afterwinds, that raised dirt and debris from the surface, forming the stem of what would become known as a mushroom cloud. The particles of the cloud, which were highly radioactive, were eventually dispersed by the wind.
The bomb’s core, a sphere of plutonium in the center of a sphere of uranium, is surrounded by explosive charges and detonators.
Detonating the explosives simultaneously causes the plutonium to be dramatically compressed, increasing its density and initiating an uncontrolled nuclear reaction.
Sources: Department of Defense; “The Effects of Nuclear Weapons”; nuclearsecrecy.com; wsmr.army.mil; 1945 report on the Trinity Test by Gen. L.R. Groves.