The Manhattan Project Bomb You Haven’t Heard Of
Two atomic bombs nicknamed Little Boy and Fat Man were detonated over Hiroshima and Nagasaki in August 1945, effectively ending World War II. The U.S. had rushed headlong into the development of the bombs, trying to develop the unprecedented nuclear weapons before the Nazis did, and succeeded.
Manhattan Project scientists built at least four bombs—Little Boy, Fat Man. the Gadget, and Thin Man. The first three made it to fruition, and the first two became the only atomic bombs ever deployed in war. Thin Man never saw the light of day.
How to the Atomic Bombs Were Built
There are two different ways to build an atomic bomb. One is gun-type assembly, in which a hollow, sub-critical (less mass than needed to sustain a chain reaction) fissile “bullet” is shot at a solid supercritical (able to sustain a chain reaction) core. The bullet strikes and compresses the core, fission happens, and the bomb explodes. This type of assembly is relatively simple in design, involving one thing being shot at another.
The second type of assembly is a bit more complex. Implosion-type assembly involves a hollow sphere containing an intricate arrangement of high explosives and detonators, surrounding a solid fissile, but not yet supercritical, core. The high explosives are detonated in such a way that the blast wave compresses the core to a supercritical density. This causes fission, which makes the bomb explode.
Thin Man was a gun-type weapon designed to use plutonium as fuel. But scientists found that the reactor-produced plutonium available at the time contained too many impurities, causing a greatly increased spontaneous fission rate—meaning that the fuel would pre-detonate and blow itself apart while trying to attain criticality, rather than after. It would be putting the nuclear cart before the horse. So the bomb was scrapped, and focus turned to Little Boy.
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