The United States of America dropped the world's first operational atomic bomb above the Japanese city of Hiroshima at 8:15 a.m on the 6th of August 1945. It was carried to its target by the United States Army Airforce (USAA) B-29 bomber Enola Gay, flying from the American airbase on the Pacific island of Tinian. Nicknamed 'Little Boy', the bomb exploded with the equivalent force of over 12 Kilotons of TNT. Around 5 square miles of the city was reduced to ashes, with over 60% of the total building stock destroyed. Within four days of the blast, 120,000 civilian inhabitants had died, many of the civilians were instantly vaporised by the explosion. Three days later, at around 11 a.m on the 9th of August, another B-29 bomber from the Tinian airbase dropped the second operational atomic bomb on Nagasaki. This bomb was nicknamed 'Fat man' and had a similar impact to the Hiroshima bomb, approximately 2.5 square miles of the city was laid waste, and over 70,000 people killed as an immediate result of the blast. Imperial Japan announced unconditional surrender on the 15th of August and formally signed on the 2nd of September 1945, ending the Second World War.
Nuclear Fission occurs when a nucleus of a heavy atom splits through natural radioactive decay or instigated in a controlled environment by absorbing a neutron, producing two smaller nuclei and releasing a lot of energy.
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In 1909, Austrian physicist Lise Meitner and German chemist Otto Hahn partnered together in Germany to study how different substances produced different types of radiation. In 1934, Italian physicist Enrico Fermi discovered that if you bombard atoms with neutrons, you can make them undergo radioactive decay, where they release particles and become slightly lighter elements. Meitner, Hahn and another scientist named Fritz Strassmann started their bombardment experiments to try and figure out how these reactions worked.
In March 1938, Meitner having Jewish ancestry, had to escape from Germany to Stockholm, Sweden, where she continued to correspond with Hahn about their ideas and experiments. In November 1938, Hahn secretly left Germany to share some strange results with Meitner. When they bombarded uranium with neutrons, one reaction product looked like radium, lighter than uranium. They thought it was radium because of how it reacted with other atoms and molecules, but they couldn't figure out how bombarding uranium with neutrons would produce radium.
Hahn returned to Germany, where he and Strassmann studied the radium product from the experiment and found that it was not radium at all; it was barium, a much smaller element about half the uranium's weight. Hahn and Strassmann could not understand how the bombardment of neutrons could make uranium turn into a whole different element half its size. Hahn kept communicating with Meitner, asking for her help. Meitner being in exile made Hahn and Strassmann submit the paper to a German scientific journal describing their scientific results.
Meitner and her nephew Otto Frisch, a nuclear physicist, worked together where Meitner proposed an idea in which she imagined atomic nuclei as liquid droplets. This idea made Meitner realise that when a neutron hits a uranium nucleus, it could make the nucleus stretch out, pinch together in the middle, and then split into two nuclei, just like one drop of water splitting into two smaller droplets. She and Frisch found that the larger uranium atom would split into two lighter elements - barium and krypton releasing a lot of energy along with many neutrons. Meitner discovered Nuclear Fission. Meitner couldn't publish a paper with Hahn and Strassmann as she was in exile, so Meitner and Frisch published their conclusions in the journal Nature in 1939.
Nuclear Fission has great potential as a source of energy. It is a relatively simple way to produce huge amounts of energy compared to other sources, which is the primary use today in nuclear power plants. Nuclear fission produces two or more neutrons that induce further fissions. This process is known as the nuclear fission chain reaction. It is a self-propagating sequence of fission reactions, which release a vast amount of energy. This process occurs in a proper multiplication environment under controlled conditions (Nuclear Reactors).
Meitner realised that the discovery of nuclear fission had destructive potential, and she warned about this in her journal. Germans knowing the discovery of atomic fission through Hahn and Strassmann alarmed other scientists. With the help of Albert Einstein, Leo Szilard and Enrico Fermi, the physicists in the U.S. wrote a letter to President Roosevelt explaining the danger of weaponisation of this discovery by Nazi Germany. Ironically, all three scientists had Jewish ties and were refugees in the U.S. escaping from the Nazis and the Fascists; therefore, they understood the situation. The President formed a committee and funded Fermi and Szilard at Columbia University to conduct their research in radioactive isotope separation. The name of this committee kept changing, and in 1941, it was named the Office of Scientific Research and Development (OSRD).
An atomic bomb requires an explosive source which needs to be an unstable radioactive isotope of uranium or plutonium. Leo Szilard, a German physicist, was the first scientist to theorise that scientists could use nuclear materials to create energy from self-propagation in nuclear fission.
Natural uranium contains two isotopes, uranium-235 and uranium-238, where uranium-238 is much more abundant. Uranium-238 is not fissionable as it becomes more stable by becoming uranium-239 when bombarded by neutrons. In contrast, uranium-235 becomes more unstable and fissionable by becoming uranium-236 when bombarded by neutrons. The scientists from OSRD investigated four methods: gaseous diffusion, liquid thermal diffusion, electromagnetic separation and centrifuge, to separate the two isotopes of uranium. Fermi and Szilard successfully enriched the uranium to produce uranium-235, the fissionable component. The scientists combined uranium with fluorine to form a gas to filter the extract isotope that they wanted (gaseous diffusion). In 1942, underneath the University of Chicago rugby stadium, Enrico Fermi created the first controlled nuclear chain reaction named 'Chicago Pile 1'. Meanwhile, supported by the Canadian government and military, Glenn Seaborg was developing microscopic samples of pure plutonium.
The scientists believed that the Nazis were already developing the atomic bomb. President Roosevelt's initiation of 'The Manhattan Project' was to produce an atomic bomb before the Nazis. In 1942, the OSRD formed the Manhattan Engineer District when the Army Corps of Engineers joined the OSRD. Manhattan project was the code name of this military programme lead by American physicist J. Robert Oppenheimer and U.S. Army Colonel Leslie R. Groves. The project was costly, and it took place over four years in three different locations: Los Alamos, New Mexico, Oak Ridge, Tennessee and Richland, Washington.
The project needed several pieces of research simultaneously in a limited time, such as finding out the exact amount of uranium-235 needed to achieve critical mass. In 1943, many scientists moved to the U.S. to join the project after establishing a combined policy committee with Great Britain and Canada. In 1943, J. Robert Oppenheimer had already begun designing and building the first Manhattan project bombs in Los Alamos, New Mexico laboratory. In 1944, The U.S. started mining natural uranium-238 from the Navajo Nation in Arizona.
The Trinity test, which is the first-ever testing of an atomic bomb, took place on the 16th of July, 1945. The U.S. did this test in Alamogordo, New Mexico, a remote desert location. The scientists did the Trinity test in a controlled environment where scientists could analyse the results remotely from a distance. People felt the heat from the blast 10 miles away and described the explosion as bright as the sun. The Trinity test blast had an explosive power of 20,000 tons of TNT and created a 40,000 feet high mushroom of clouds. The Trinity test bomb was named 'The Gadget', and it was plutonium fuelled bomb.
Oppenheimer developed two more bombs, 'the little boy' gun-type design with uranium-235 as its nuclear source and 'the fat man' was developed with implosion assembly method that used plutonium-239 source. The plutonium core bomb had to use the implosion assembly method due to some issues. The University of Chicago developed the only method for obtaining plutonium-239, which was through transmutation in a reactor pile of uranium-238. The isotope plutonium-239 is ideal for nuclear fission, whereas plutonium-240 has a relatively higher spontaneous rate, lowering the energy for the bomb's detonation. The isotope of plutonium-240 increases the risk of pre-detonation. For plutonium production, the manhattan project built a reactor on the Colombia river near Washington, the Hanford Engineer Works. The Hanford reactor produced less pure plutonium-239 and had traces of plutonium-240. Physicist Seth Neddermeyer at Los Alamos overcame this problem by incorporating conventional explosives around a central plutonium mass. He thought that increased density would allow plutonium to reach its critical mass; the explosives would ignite and release shock wave that would compress the inner plutonium for detonation.
A single scientist is not responsible for the development of the atomic bomb. Brilliant minds from all over the world joined 'The Manhattan Project' to create a weapon of mass destruction against Nazi Germany before they have gained such destructive power for themselves. The Manhattan project had employed nearly 130,000 employees, and its cost was around $2 Million, which, according to this date, is roughly $25 Million. The Allied forces did not use the Atomic bomb against Germany as the allied forces had already invaded France and defeated Germany.
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