核弹英文资料

The atomic bomb originated in 1939. Doctor Albert Einstein convinced Franklin Roosevelt to fund development of the bomb. U.S. scientists worked in extreme secrecy to finish the bomb, which they told the Army was ready for use by 1943. On August 6, 1945, the B-29 flew struck Hiroshima, Japan, on the world's first atomic bombing mission. Three days later another fighter-bomber dropped the plutonium bomb on Nagasaki. The Japanese surrendered in the following days thereby ending World War II.These are bombs whose huge explosive power is caused by a sudden release of energy resulting from the splitting of nuclei of a heavy chemical element such as plutonium or uranium by neutrons in a very rapid chain reaction.Uranium Bomb-the nuclear bomb that was dropped on Hiroshima was a gun-type uranium bomb. Uranium is supposedly the material of choice for terrorists since the design is simple, although highly enriched U-235, the main element, is not easy to make.Plutonium Bomb-the bomb dropped on Nagasaki was a plutonium bomb, using the element Pu-239. Plutonium is not hard to obtain and is produced in most nuclear reactors. It can then be separated using chemistry. A higher component of the element, Pu-240, is highly radioactive and often tends to pre-detonate bombs before the chain reaction is complete. An implosion design is used to prevent this, but because the process is difficult, it isn't very likely a small terrorist group could do it without some sort of state help.The United Nations has proclaimed April 26, International Day in Memory of Chernobyl, Ukraine, where a nuclear reactor accident had taken place in 1986.