Nuclear Fission
In 1933, Hungarian inventor and physics instructor Leo Szilard conceived of the idea of nuclear fission. "[I]t … suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbs one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction …. I didn't see at the moment just how one would go about finding such an element, or what experiments would be needed, but the idea never left me. In certain circumstances it might be possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs." Intrigued by this theory, Italian physicist Enrico Fermi bombarded at least 63 different elements with neutrons. In so doing, he discovered that uranium reacted differently than any other element. Most elements were somewhat altered after being hit by neutrons, but the uranium nuclei seemed to break into two equal pieces. No one understood what had really happened to the uranium.
On December 21, 1938, two German chemists named Otto Hahn and Fritz Strassman set up a similar experiment in their lab. They placed a piece of uranium beside a radioactive element. A radioactive atom has an unstable nucleus, so neutrons shoot out of its nucleus at high speeds. The chemists used the radioactive element to bombard the uranium with neutrons. At first, their results seemed just as baffling as Fermi's. The force of the crash seemed to be splitting the uranium atom in two, which was then believed impossible.
Hahn turned to his former partner, Lise Meitner, for an explanation. Lise Meitner brought up the topic with her nephew (and fellow physicist), Otto Frisch. They discussed the Danish physicist Niels Bohr's idea that the nucleus of an atom might act like a droplet of liquid and determined that the force of the collision between particle and atom had caused the uranium nucleus to stretch until it split. After extensive calculations, they concluded that if such a division were to take place, it would release an enormous amount of energy. They called this process "fission."
In 1933, Hungarian inventor and physics instructor Leo Szilard conceived of the idea of nuclear fission. "[I]t … suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbs one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction …. I didn't see at the moment just how one would go about finding such an element, or what experiments would be needed, but the idea never left me. In certain circumstances it might be possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs." Intrigued by this theory, Italian physicist Enrico Fermi bombarded at least 63 different elements with neutrons. In so doing, he discovered that uranium reacted differently than any other element. Most elements were somewhat altered after being hit by neutrons, but the uranium nuclei seemed to break into two equal pieces. No one understood what had really happened to the uranium.
On December 21, 1938, two German chemists named Otto Hahn and Fritz Strassman set up a similar experiment in their lab. They placed a piece of uranium beside a radioactive element. A radioactive atom has an unstable nucleus, so neutrons shoot out of its nucleus at high speeds. The chemists used the radioactive element to bombard the uranium with neutrons. At first, their results seemed just as baffling as Fermi's. The force of the crash seemed to be splitting the uranium atom in two, which was then believed impossible.
Hahn turned to his former partner, Lise Meitner, for an explanation. Lise Meitner brought up the topic with her nephew (and fellow physicist), Otto Frisch. They discussed the Danish physicist Niels Bohr's idea that the nucleus of an atom might act like a droplet of liquid and determined that the force of the collision between particle and atom had caused the uranium nucleus to stretch until it split. After extensive calculations, they concluded that if such a division were to take place, it would release an enormous amount of energy. They called this process "fission."
The Possibility of An Atomic Bomb
This news was shared with Niels Bohr, who exclaimed, "Oh what idiots we have all been! Oh but this is wonderful! This is just as it must be!" He announced the discovery at the Fifth Washington Conference on Theoretical Physics in January 1939 and it quickly spread. I heard of the discovery from one of my fellow professors at the University of Columbia. He had read in the San Francisco Chronicle that some German chemists had found that the uranium atom could be split by a neutron. I couldn't get my mind off of it all day.
It quickly became obvious to myself and many other physicists that an atomic bomb might actually be possible. It was both a frightening and exciting idea. Leo Szilard, alarmed that the discoveries being made might help the German scientists working for Hitler to create an atomic bomb, took action. He made an attempt to get other nuclear physicists to consent to not publish papers about their work. When this failed, he decided (along with his friends Eugene Wigner and Edward Teller) to notify the United States government of the danger of an atomic bomb in the hands of the Nazis. The trio enlisted Albert Einstein (likely the most well-known scientist in the world at the time) to help them get the president's attention. Even though Einstein and Szilard did get President Roosevelt to take action, little progress was actually made on the project until 1942, after the bombing of Pearl Harbor.
Throughout the spring of 1942, research focused on obtaining enough fissionable material to create a chain reaction. In laboratories across the United States, teams of scientists worked to solve this dilemma. The rare isotope of uranium called U-235 (one of the only known fissionable materials) needed to be separated from the more abundant U-238, and they knew of no good way to do this. All of the methods that had so far been devised were extremely painstaking. Scientists in Great Britain figured out that a vast industrial plant would do the trick, it would just come at an extremely large expense.
Then Emilio Segrè discovered that plutonium-239 was also fissionable material. A chain reaction with natural-occurring uranium produced by fast neutrons would lead to the formation of a certain amount of plutonium. Now there were two ways to build a bomb.
The need to build secure, vast industrial plants got the project handed off to the Army Corps of Engineers. They had experience with large construction projects and military security. Colonel James C. Marshall was appointed to head the endeavor, and he set up the Manhattan Engineer District in New York City as headquarters. From then on, the program was known as the Manhattan Project.
As was evident from the way he proceeded with the project, Colonel Marshall lacked the boldness and familiarity with physics required to be successful, and so he was replaced by Colonel Leslie R. Groves (later General Leslie R. Groves). Groves was just the man for the job- demanding and decisive, intelligent, energetic, and self-confident. Some later called him "the Manhattan Project's indispensable man."
This news was shared with Niels Bohr, who exclaimed, "Oh what idiots we have all been! Oh but this is wonderful! This is just as it must be!" He announced the discovery at the Fifth Washington Conference on Theoretical Physics in January 1939 and it quickly spread. I heard of the discovery from one of my fellow professors at the University of Columbia. He had read in the San Francisco Chronicle that some German chemists had found that the uranium atom could be split by a neutron. I couldn't get my mind off of it all day.
It quickly became obvious to myself and many other physicists that an atomic bomb might actually be possible. It was both a frightening and exciting idea. Leo Szilard, alarmed that the discoveries being made might help the German scientists working for Hitler to create an atomic bomb, took action. He made an attempt to get other nuclear physicists to consent to not publish papers about their work. When this failed, he decided (along with his friends Eugene Wigner and Edward Teller) to notify the United States government of the danger of an atomic bomb in the hands of the Nazis. The trio enlisted Albert Einstein (likely the most well-known scientist in the world at the time) to help them get the president's attention. Even though Einstein and Szilard did get President Roosevelt to take action, little progress was actually made on the project until 1942, after the bombing of Pearl Harbor.
Throughout the spring of 1942, research focused on obtaining enough fissionable material to create a chain reaction. In laboratories across the United States, teams of scientists worked to solve this dilemma. The rare isotope of uranium called U-235 (one of the only known fissionable materials) needed to be separated from the more abundant U-238, and they knew of no good way to do this. All of the methods that had so far been devised were extremely painstaking. Scientists in Great Britain figured out that a vast industrial plant would do the trick, it would just come at an extremely large expense.
Then Emilio Segrè discovered that plutonium-239 was also fissionable material. A chain reaction with natural-occurring uranium produced by fast neutrons would lead to the formation of a certain amount of plutonium. Now there were two ways to build a bomb.
The need to build secure, vast industrial plants got the project handed off to the Army Corps of Engineers. They had experience with large construction projects and military security. Colonel James C. Marshall was appointed to head the endeavor, and he set up the Manhattan Engineer District in New York City as headquarters. From then on, the program was known as the Manhattan Project.
As was evident from the way he proceeded with the project, Colonel Marshall lacked the boldness and familiarity with physics required to be successful, and so he was replaced by Colonel Leslie R. Groves (later General Leslie R. Groves). Groves was just the man for the job- demanding and decisive, intelligent, energetic, and self-confident. Some later called him "the Manhattan Project's indispensable man."