While the Manhattan Project was developing plutonium production facilities and producing plutonium at Hanford, Washington in the early 1940s, the Project was also working on the design of a bomb that would utilize the plutonium. It turned out that gun-type design being worked on for a uranium bomb would not work for a plutonium bomb. Plutonium-239 was being produced in reactors but the reactors were also creating plutonium-240 as well. P-240 spontaneously fissions and produces neutrons. In a gun-type bomb, these extra neutrons would cause the bomb to explode early before a full critical mass of plutonium was formed. The resulting fizzle blast would be much weaker than a full nuclear explosion.
After ruling out the gun-type bomb design, work was begun in 1944 at Los Alamos, New Mexico n a new implosion bomb design. The design was based on a sphere of plutonium with a neutron initiator at its core. The sphere was to be surrounded by conventional explosives that had different burn rates. When arranged properly and triggered in the right time sequence, the explosives would create a compression wave focused inward. This compression wave would compact the plutonium sphere into a smaller sphere that was much denser than the original sphere. Because the critical mass is a function of density in a volume, the amount of plutonium would be a critical mass in the smaller sphere. The neutron initiator was included to insure that the reaction triggered properly.
On benefit of this design was that it required much less plutonium than the amount of uranium needed for a gun-type bomb. The implosion design only required about fourteen pounds of plutonium. The new design was very complex and pushed the state of the art for creating a compression effect. While the gun-type design was simple and reliable enough that it was not felt that a test was needed, the implosion design was so new and difficult that it was decided to create and test such a bomb before deploying it as a weapon. The test bomb was code named “the Gadget.”
The Gadget was constructed and a new test site was created in New Mexico near Alamogordo during the first half of 1945. Laboratory leader J. Robert Oppenheimer named the site Trinity in reference to a poem by John Dunne. A one hundred foot steel tower was constructed for the test to simulate the air burst of an actual bomb to maximize effect. The components were assembled in July of 1945.
Early on July 14th, 1945, the Gadget was detonated in a blast equivalent to twenty kilotons of TNT. The blast created a crater of radioactive glass below the tower. The shock wave was felt over one hundred miles away. The mushroom cloud towered to about eight miles in the sky. The very first nuclear blast ever created by the human race lit up the surround mountains brighter than the sun and awed everyone who directly witnessed it. There were a number of reports in the area of a huge bright explosion which was explained as the explosion of an ammunition magazine to the media. Oppenheimer later remarked that he was reminded of a passage in the Hindu Bhagavad Gita; “Now I am become Death, the destroyer of worlds.”
This is a photograph of the Trinity fireball sixteen milliseconds after detonation:
