The Manhattan Project was a secret program initiated by the United States government to develop the atomic bomb. It resulted from the apprehensions of American scientists that the Germans, specifically the Nazis, were aggressively developing nuclear bombs. Famous physicist Albert Einstein had written a letter to President Franklin D. Roosevelt to inform him about the Germans’ nuclear ambitions just before the beginning of World War II. He concluded that the world would be at a great risk if the Germans succeeded in building atomic bombs. Roosevelt gave approval for the formation of uranium research sites. Apart from the US, there was also immense contribution from the UK and Canada.
In many ways, the idea of creating atomic bombs can be traced back to discoveries by Ernest Rutherford about the nature of atoms that emit radiation, such as uranium, the discovery that atoms have a nucleus and that one element can be changed into another, in his case, turning nitrogen into oxygen, by deliberately causing a nuclear reaction..Rutherford, along with several of his students and colleagues, participated in the Manhattan Project.
In 1941, Eugene Booth and John Dunning successfully separated Uranium-235 from Uranium-238, and extensive research into nuclear fission reaction followed. (Nuclear fiction reaction is the splitting apart of an atom's nucleus, releasing tremendous amounts of energy.) Further research by Enrico Fermi revealed the destructive nature of Uranium-235, and this led to the “dream” of making an atomic weapon.
Around the same time, a new element called plutonium was discovered by Glen Seaborg. Soon, research into plutonium showed that it has similar properties as Uranium-235, though it is comparatively less fissile (able to support a nuclear fission reaction). It was later discovered that Uranium-238 could be converted into Plutonium-239 when exposed to alpha particles under suitable conditions. This discovery became the turning point in the development of atomic weapons.
By this time, the atomic bomb was already created on a scientific basis, but it was in the form of a nuclear reactor, which was obviously not suitable for aerial bombing. The very first design of an atomic bomb used Uranium-235 in a gun detonator. The purpose of the device was to achieve simultaneous collision and fusion of critical masses of Uranium-235. In this case, the sphere of Uranium-235 was placed at the center of the bomb, and it was surrounded by explosives to facilitate the propulsion of the U-235 bullet.
The device for Plutonium-239 was different. Its outer sphere was made from beryllium and polonium, and Plutomium-239 was placed in equal sections at the center. Explosives were placed around the sphere, and the inner plutonium would merge together to form critical mass and cause fission during detonation. The volume of plutonium must be constant throughout the reaction for successful fission. In spite of the paucity of time, uncertainty of the success of the bomb, and engineering difficulties, the bombs were finally designed.
On July 16, 1945, the first test of a nuclear weapon was carried out by the United States at the White Sands Proving Ground, near Socorro, New Mexico. The test was named “Trinity”, and it resulted in an explosion that measured approximately 20 kilotons.
The justification for the use of atomic bombs during World War II was under debate, with those against the idea blaming both scientists and military operators for irresponsible use of a scientific discovery. As the Manhattan Project progressed, scientists were more focused on their remarkable discoveries than on their consequences. In due time, they realized how the bomb was going to be used. Some of them considered quitting the project on moral grounds, refusing to contribute to the destruction of humanity.
Many people showed their opinions against the use of atomic weapons, reasoning that other nations would soon become atomic powers too and the peace and security of the world would be seriously threatened. Despite opposition, the United States decided to go ahead with the use of atomic bombs. The government and its supporters believed they were making the right decision, and it was the only way to end the war. They feared that the Union of Soviet Socialist Republics (USSR) would try to expand communism if the war was not stopped.
With the war in Europe ended and the United States and its allies victorious, the United States issued the Potsdam Proclamation demanding Japan's surrender. The Japanese refused and this led to the decision to use atomic bombs on Hiroshima and Nagasaki. Hiroshima was destroyed using a uranium bomb called the “Little Boy” on August 6, 1945, and a plutonium bomb called the “Fat Man” was dropped on Nagasaki on August 9, 1945. The first bomb took the lives of around 200,000 people, while the second one killed almost 140,000.
More about the Manhattan Project can be found in the following websites: