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After a lot of thinking I decide to write about the Manhattan project because it was the first experience that mankind had with nuclear power. For one way or another it also cheap the way people think about nuclear power today. So to understand everything in this experience we have to understand the history events that led to it.World War II erupted at a moment when the promise of atomic energy had progressed from being possible to being probable. Every one could imagine the fear of what will happen if the Nazi Germany put their hands in this kind of power. However was not clear whether this energy could be released explosively. For a project like this to born it need a man of vision a man of believe of the project success and more importantly a man of action that man was Leo Szilard. He succeeds to squeeze a letter from Albert Einstein about the possibility of nuclear weapon. This letter is known as the Einstein Letter and it was addressed to President F.D. Roosevelt. Ten days after the letter was delivered the first meeting of the Advisory Committee on Uranium (the “Briggs Uranium Committee”) was held in Washington, DC on Pres. Roosevelt’s order.

Szilard and Einstein Together After the War

Due largely to persistent official lack of interest, the progress on the subject was desultory and inconclusive in the United States. The next key developments occurred in the United Kingdom. However through 1940 and well into 1941, work accelerated in the U.S., and important discoveries accumulated although official interest and support languished. In February, 1941 Philip Abelson began actual development of a practical uranium enrichment system (liquid thermal diffusion) and on February 26 Glenn Seaborg and Arthur Wahl discover plutonium. During March the first American measurements of the U-235 fission cross section allow Peierls to calculate the first experimentally supported estimate of a critical mass for U-235 (18 lb as a bare sphere, 9-10 lb when surrounded by a reflector). By July 1941 plutonium was demonstrated to be a superior fissile material, and the MAUD Committee completed its final report, describing atomic bombs and project propsals for building them in some technical detail.

Lawrence_Compton_Bush_Conant_Compton_Loomis_83d40m_March_1940_meeting_UCB

Compton asked the theoretical physicist J. Robert Oppenheimer of the University of California, Berkeley, to take over research into fast neutron calculations—the key to calculations of critical mass and weapon detonation—from Gregory Breit, who had quit on 18 May 1942 because of concerns over lax operational security. John H. Manley, a physicist at the Metallurgical Laboratory, was assigned to assist Oppenheimer by contacting and coordinating experimental physics groups scattered across the country. Oppenheimer and Robert Serber of the University of Illinois examined the problems of neutron diffusion—how neutrons moved in a nuclear chain reaction—and hydrodynamics—how the explosion produced by a chain reaction might behave. To review this work and the general theory of fission reactions, Oppenheimer convened meetings at the University of Chicago in June and at the University of California, Berkeley, in July 1942 with theoretical physicists Hans Bethe, John Van Vleck, Edward Teller, Emil Konopinski, Robert Serber, Stan Frankel, and Eldred C. Nelson, the latter three former students of Oppenheimer, and experimental physicists Felix Bloch, Emilio Segrè, John Manley and Edwin McMillan. They tentatively confirmed that a fission bomb was theoretically possible.

There were still many unknown factors. The properties of pure uranium-235 were relatively unknown, as were those of plutonium, an element that had only been discovered in February 1941 by Glenn Seaborg and his team. The scientists at the Berkeley conference envisioned creating plutonium in nuclear reactors where uranium-238 atoms absorbed neutrons that had been emitted from fissioning uranium-235 atoms. At this point no reactor had been built, and only tiny quantities of plutonium were available from cyclotrons. Even by December 1943, only two milligrams had been produced. There were many ways of arranging the fissile material into a critical mass. The simplest was shooting a “cylindrical plug” into a sphere of “active material” with a “tamper”—dense material that would focus neutrons inward and keep the reacting mass together to increase its efficiency. They also explored designs involving spheroids, a primitive form of “implosion” suggested by Richard C. Tolman, and the possibility of autocatalytic methods, which would increase the efficiency of the bomb as it exploded.

Considering the idea of the fission bomb theoretically settled—at least until more experimental data was available—the Berkeley conference then turned in a different direction. Edward Teller pushed for discussion of a more powerful bomb: the “super”, now usually referred to as a “hydrogen bomb”, which would use the explosive force of a detonating fission bomb to ignite a nuclear fusion reaction in deuterium and tritium. Teller proposed scheme after scheme, but Bethe refused each one. The fusion idea was put aside to concentrate on producing fission bombs. Teller also raised the speculative possibility that an atomic bomb might “ignite” the atmosphere because of a hypothetical fusion reaction of nitrogen nuclei. Bethe calculated that it could not happen, and a report co-authored by Teller showed that “no self-propagating chain of nuclear reactions is likely to be started.”[  In Serber’s account, Oppenheimer mentioned it to Arthur Compton, who “didn’t have enough sense to shut up about it. It somehow got into a document that went to Washington” and was “never laid to rest”.

At the 6 august and the 9 august all mankind witness the most brutality act in the history 35,000 people were killed and 60,000 injured.Citys were destroyed hops were lost and some men ginned power and victory. No one can change what happen that day and the nuclear power approved the strength that hold. Maybe that the problem nuclear power facing the fear of it fall at the wrong hands and be used like the sixth of august 1945. However since that day we never had a nuclear bombing and all the research are heading in way that make it safer every day. The third Newton law of motion stat “that action and reaction are equal and they have opposite direction”. We as human we can make a good use of that power in greeting good as we did in the other side. Overall since the attack on Japan no one used nuclear bomb and a lot of nuclear power plant were bulled to generate electricity.Untill now the nuclear power appear to be the cleanest sours of power we use. And for over 60 years of using that power only three accidents happened one of them was by nature (Fukushima Daiichi nuclear disaster) .So at the end the nuclear power is one of the most important Invention we have in our history and it also cheap our life today.

Reference:

http://nuclearweaponarchive.org/Usa/Med/Med.html

http://en.wikipedia.org/wiki/Manhattan_Project

 

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