Once discovered, the basic physics underlying the bomb seemed almost simple: bombard a uranium nucleus, and the resulting split atom would release a huge amount of energy. But if the basic principle was simple, the physics entailed in the construction of the bomb itself was anything but. The physicists needed to figure out how to produce enough radioactive material, as there was not nearly enough to be found in nature. They needed to find a way to create a nuclear chain reaction they could control, and then they needed to figure out how to control the speed of a fast nuclear reaction, so that it would release energy quickly enough to create a super-powerful bomb but not so quickly that the bomb would explode too soon. And, of course, they needed to figure out what would happen after a nuclear explosion; there was a question at the outset, for example, whether such an explosion would vaporize the atmosphere and destroy all life on earth.

Perhaps the most difficult and most crucial problem that Oppenheimer and his team faced was the design of the bomb mechanism itself. How could they create a mechanism that would release the immense power of nuclear fission on command? In a triumph of theoretical and applied physics, the Los Alamos group eventually came up with two workable bomb designs, code-named "Little Boy" and "Fat Man."

Little Boy, the U-235 bomb, had the simpler design of the two, and the physicists were certain that it would work. The mechanism used a gun-assembly method, in which one subcritical mass of U-235 is fired at another subcritical mass of U-235. When the two join, they form a critical mass and ignite in a nuclear reaction. This is the type of bomb which was dropped over the Japanese city of Hiroshima.

Fat Man, the plutonium bomb, used a different method: the implosion method. In the Fat Man bomb, a subcritical sphere of plutonium is surrounded by explosives, and when the explosives fire, a shock wave compresses the plutonium into a critical mass, setting off a nuclear reaction. It was the Fat Man bomb that was dropped over Nagasaki, Japan. As this method was somewhat more complicated than the gun-assembly method, scientists were less sure it would work, and decided to test it out.

As the scientists were celebrating their breakthrough, foremost in their mind was the thought that they had done it, they had beaten Germany to the creation of the bomb. After all, the race against Germany had been the driving purpose of the Manhattan Project and the reason given by many of the physicists involved for why they were so passionately committed to the bomb effort.

But how real was the German threat? In 1944, as the Los Alamos physicists were readying themselves for a test of the nuclear bomb, the American government finally learned the status of the German nuclear program.

In June of 1944, the Allies invaded France. A special team sent in by General Groves was charged with discovering how far German nuclear development had progressed. As the Allies pushed further and further into the continent, Groves's special team was able to report back: the German nuclear program had barely existed.

In 1940, the Germans had started investigations into the possibilities of nuclear power, but in 1942, they stopped. This was probably due in part to Hitler's lack of vision; he was unable to see the potential of nuclear weapons. Also, pro-German, anti-Nazi physicists who were unwilling to hand over such a dangerous weapon to Hitler may have sabotaged the bomb project from the inside. Whatever the reason, the nuclear program had been cast aside, and by December of 1944, the United States was aware of this.

The Manhattan Project had been intended to get the bomb before Germany; the United States now knew that Germany would never have the bomb. And yet the project continued unabated. The swift progress continued even after the German surrender. In fact, Oppenheimer later remembered this as the period in which the Los Alamos physicists worked the hardest.

The United States government had its own reasons for continuing with the Manhattan Project. For one thing, there was still Japan with which to contend–the country showed no sign of backing down, and the war in the Pacific was still going strong. For another, the Soviet Union was waiting in the wings as a potential American enemy, and some historians have speculated that farsighted American leaders anticipated the post-war Cold War and had always wanted the bomb for use against the Soviet Union, rather than the Axis forces.

But whatever the government's reasons, the question remains: why did the scientists at Los Alamos continue their work without pause, even after the German surrender? Were they blinded by their excitement over the technical and scientific breakthroughs? Whether or not this was the case among some of the residents at Los Alamos, it cannot be said that Oppenheimer and the majority of his colleagues were blind to the political and moral implications. Oppenheimer and Bohr had even started holding discussions among the scientists at Los Alamos, providing a forum for scientists to discuss the dangers and possibilities of nuclear power. As they later explained in numerous speeches and memoirs, these scientists were well aware of the dangers that accompanied their discoveries, but they felt strongly the duty to protect their country and believed that succeeding in the creation of the atomic bomb was the best and only way they could effectively do so.

If any of the scientists at Los Alamos did blind themselves to the larger ramifications of the atomic bomb, choosing instead to focus on solving the technical problems of the "gadget," as the bomb was commonly called, they were about to get a wake up call that no one could have ignored. In 1945, the scientists at Los Alamos would finally see their work come to fruition and would fully realize the devastating power of their creation.

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