Before the Uranium-235 "Little Boy" bomb was finished, another bomb was proposed. The Uranium-238 that had been earlier ruled out as an option was now being looked at. The Uranium- 238 could capture a free neutron without fissioning and become Uranium-239. But the Uranium- 239 produced is unstable(radioactive) and decays first to Neptunium-239 and then to Plutonium- 239. This proved to be very useful discovery because the newly created plutonium-239 is fissionable and it can be separated from the uranium by cheimcal techniques, which would be far simpler than the physical processess to seperate the Uranium-235 from the Uranium-238.
The problem to overcome in the design of the plutonium bomb was an isotope of plutonium. Scientists feared this isotope would explode prematurely and most of the plutonium would blow apart beofore it could all fission. To overcome this defect, the plutonium had to be brought inot a supercritical mass far faster than conventioanl ballistics could achieve.
Physicist Seth Neddermeyer and mathematicitan John von Neumann devised the theory of implosion. A small sphere of plutonium was surrounded by chemical high-explosives. When the 5,300 pounds of explosives were all detonated, they focused the blast wave to compress the plutonium instantly into a supercritcal mass. This was a much more complex theory than the Uranium bomb, and many people doubted that it would work.
There was a hugh debated back at the labortory over whether to test the new plutonium bomb before it was actually dropped. Many of the experts were afraid that if the test failed, the precious plutonium would be scattered all across the countryside. And the other argued that if an untested plutonium bomb was dropped and it failed, that the enemy would find themselves with a gift atomic weapon. The final agreement for the test was that the bomb would be placed in a gigantic, 214-ton cylinder-shaped tank(called "Jumbo"). If the plutonium correctly fissioned, the tank would be vaporized. If it did not workd correctly, the conventional explosives woudl be contained in the tank and the plutonium would stay in the tank. Later on the scientists were afraid that such a large tank would distort their communication, and detonating equiptment with the bomb, so it was never used.
See the section on Trinity to learn about the test.
Copyright @1998 Matt Fields