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| | Investigators from the United Nations are all but convinced that a number of governmental leaders in Pakistan knew that the country's top atomic scientist was giving other nations nuclear technology and information. This scientist particularly was supplying North Korea with nuclear information. It is also thought that some terrorist groups have benefited from information provided by this Pakistani scientist over the years. In regard to equipment that has been sold, the most common items are uranium enrichment centrifuge components which appear to have gone to Libya and Iran. Libya actually finally did confess to having had a program to develop weapons of mass destruction -- which that country says has not been brought to an end. Iran has denied that it has such a program and intends to use nuclear technology only for peaceful means.
“The Manhattan Project”:
First nuclear weapon was developed at the end of World War II in 1944, within the frameworks of American top-secret “The Manhattan Project” under the supervision of Robert Oppengeimer. First bomb was tested in USA during routine tests on July 16, 1945. Second & third were dropped by Americans in August of the same year on Japanese cities of Hiroshima (August 6) & Nagasaki (August 9) –this is the first & only combat use of nuclear weapons in the history of mankind.
Working principle:
Uncontrolled nuclear fission chain reaction is main principle of nuclear weapon. Two basic schemes exist: “cannon”, otherwise called ballistic & implosion. “Cannon” scheme is characteristic for the most primitive models of 1st generation nuclear weapon & also for artillery & infantry nuclear ammunition, having restrictions with respect to weapon calibre. Its aim concludes in “firing” of two units of fissionable material of sub critical mass towards each other. Given detonation method is possible only in uranium ammunitions as plutonium has higher neutron background which leads to increase in required joining speed of parts of charge, exceeding the technically achievable. Second scheme is to obtain supercritical condition through compression of fissionable material by focused shock wave, created by explosion of regular chemical explosive, with which rather difficult shape is imparted for focusing & explosion takes place simultaneously at several points with precision accuracy.
Power of nuclear charge, working exclusively on principles of fission of heavy elements, is limited to hundreds of kilotons. To develop more powerful charge, based only on nuclear fission, if it is possible, then it is extremely difficult: increase in mass of fissionable substances does not solve the problem as just begun explosion sprays part of fuel, it does not have enough time to react completely and, thus appears useless, only increasing mass of ammunition & radioactive damage of locality. Most powerful ammunition in the world, based only on nuclear fission, was tested in USA on November 15, 1952; power of explosion constituted 500 кт.
Uranium bomb:
So that reaction could support itself, corresponding “fuel” is required & uranium isotope was used as “fuel” during initial stages.
In nature, uranium is available in the form of two isotopes - uranium-235 & uranium-238. When uranium-235 absorbs a neutron, from one to three neutrons are released during disintegration process:
Uranium-238, on the contrary, during absorption of moderate-energy neutrons does not release new neutrons thus obstructing the nuclear reaction. It transforms into uranium-239, then into neptunium-239 & at last, into comparatively stable plutonium-239.
To ensure serviceability of nuclear bomb, content of uranium-235 in nuclear fuel should not be below 80 % otherwise uranium-238 quickly extinguishes nuclear chain reaction. Natural uranium consists mostly of uranium-238 (about 99.3 %). Therefore, complex & multi-stage uranium enrichment process is used during the production of nuclear fuel as a result of which, percentage of uranium-235 increases.
Bomb on uranium base was the first nuclear weapon, used by human being in combat conditions (bomb “Kid” dropped on Hiroshima). Due to number of shortages (difficulties in procurement, development & delivery), at present they are not widely used conceding to more modernized bombs on the base of other radioactive elements with lower critical mass.
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