Chemistry Name: _____________________________
Ms. Boon Period: _____ Date: ___________________
As part of our study of nuclear chemistry, we will show the movie “Fat Man and Little Boy” about Oppenheimer and the Manhattan Project. The movie is rated PG-13. If you do not want your student to watch the movie, please check the box below and he/she will be given an alternate assignment.
I do not want my student to watch the movie “Fat Man and Little Boy.” Parent Signature: ___________________________
Fat Man and Little Boy—Pre-Movie Reading and Questions
Making the Bomb
Once discovered, the basic science underlying the bomb seemed almost simple: bombard a uranium nucleus, and the resulting split atom would release a huge amount of energy. However, the physics involved in the construction of the bomb itself was very complex. The physicists had to figure out how to produce enough radioactive material because there was not a large natural source available. They also needed to determine how to control a nuclear chain reaction. Specifically, they had to learn 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. Finally, they had to figure out what would happen after a nuclear explosion. For example, there was a question whether such an explosion would vaporize the atmosphere and destroy all life on earth.
Perhaps the most difficult and most crucial problem that J. Robert Oppenheimer, creator of First Atomic Bomb, 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. 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 type of bomb 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, explosives surround a subcritical sphere of plutonium. When the explosives fire, a shock wave compresses the plutonium into a critical mass, setting off a nuclear reaction. The Fat Man bomb 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 minds was the thought that they had beaten Germany to the creation of the bomb. The race against Germany was the driving purpose of the Manhattan Project. Many of the physicists joined the project for this purpose. But how real was the German threat? In 1944, as the Los Alamos physicists readied themselves to 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 barely existed.
The Manhattan Project was intended to get the bomb before Germany. But the United States now knew that Germany would never have the bomb. Yet the project continued. 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, Japan showed no sign of backing down. 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.
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 believed that succeeding in the creation of the atomic bomb was the best way to protect the United States.
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 realize the devastating power of their creation.
The Bomb Tested
On Monday, July 16, 1945, 5:29:45 a.m., the bomb exploded. The flash of light was seen in three states. The mushroom cloud rose 38,000 feet high. The explosion itself created a half-mile wide crater in the earth, the heat of the bomb fusing the desert sand into glass. William Laurence, the only journalist allowed on the site, reported, "One felt as though he had been privileged to witness the Birth of the World–to be present at the moment of Creation when the Lord said: 'Let There Be Light.'"
Among the physicists, there was applause and cheering, a sense of triumph and relief. The gadget had worked! Oppenheimer was less than enthused. As the bomb exploded, the man perhaps most responsible for its creation instantly thought of a line from the ancient Hindu text the Bhagavad Gita: "I am become Death / The destroyer of worlds." Soon after, Oppenheimer joined in the general celebration. Everyone was thrilled that the device worked. It was only after the initial relief wore off that the scientists began to have their own second thoughts, realizing what their hard work had created: the most effective killing machine known to man.
The Trinity Test Site was more than a demonstration of the A-bomb: for some, it was a fearful reminder of what nuclear power might be capable of; for others, however, it was the triumphant realization of years of work and over two billion dollars of government money. The time had come to decide for what purpose all those years and all those dollars had served. The time had come to decide whether or not to use the bomb, not in a demonstration, but in an act of war.
President Harry Truman endlessly debated the question with his advisors–should the United States use the bomb against Japan? The only other option, Groves argued, was to invade the country, a mission that threatened the loss of over one million men. While not everyone agreed that the losses would be this high, they did agree that even 35,000 losses (a more conservative estimate) were too many to risk.
A compromise was proposed: perhaps the United States could give Japanese leaders a demonstration of the bomb's power in an uninhabited area. Surely, these reluctant physicists and politicians argued, this would be enough to convince the Japanese that they should surrender. But Oppenheimer–as well as Groves and Truman–objected to this plan, afraid that the Japanese would refuse to back down, and the element of surprise would be lost.
Eventually Truman decided that the bomb would be used against Japan. In fact, historian Martin J. Sherwin has argued that the issue was never seriously in question and that it was always assumed that the atomic bomb would be used to end the war. Oppenheimer agreed, explaining, "The decision was implied in the project."
On August 6, 1945, a B-29 bomber, the Enola Gay, dropped the Little Boy bomb on the city of Hiroshima, population 400,000. The city had been evacuated in anticipation of attack, leaving only 300,000 residents – the majority of whom were civilians. In a single instant, the bomb destroyed 70,000 buildings–over ninety percent of the city's structures. One hundred thousand people died instantly, or within a couple days of the explosion. At least 100,000 more died within five years. Three days later, on August 9, the United States dropped a second bomb, the Fat Man. This bomb was dropped on the Japanese city of Nagasaki, and it killed another 100,000 people. Five days later, the Japanese Emperor Hirohito announced his surrender.
The majority of the country supported the dropping of the bomb on Japan, as did the majority of the scientists who worked on the project. Oppenheimer was initially thrilled to hear that the bombs had worked, and it was only later that he began to fear the consequences of a nuclear world.
What was the original justification for developing the atomic bomb? How did the purpose of the project evolve as the war continued?
If you were a physicist in the 1940’s, would you work on the Manhattan Project? Why or why not?
Today, nuclear power plants provide energy to many cities. How do you weigh this use against the danger of nuclear war?