Nuclear Fission Process
Nuclear fission, the radioactive decay reaction where the heavy nucleus (uranium or plutonium) of an atom subdivided or split into two or more smaller, lighter nuclei. The decay process of nuclear fission release large amount of energy uses for preparation of atomic bomb, nuclear power reactor or atomic piles. In nuclear chemistry, the process of nuclear fission is spontaneous in some cases or going through the excitation of the nucleus with the particles like neutrons, protons, deuterons, or alpha particles or electromagnetic radiation obtained from gamma rays radiation. For example, uranium-238 spontaneous disintegration but uranium-235 does not go through spontaneous fission due to lack of activation energy.
In 1934, Italian (later naturalized American) physicist Enrico Fermi and his collaborators were engaged in studying neutron-induced radioactivity on heavy atoms of chemical elements having an atomic number greater than 92. They observed that such type of nuclear reaction produced two atomic nuclei with different atomic numbers and they are widely different from the nucleus of uranium. Therefore, uranium-235 suffers splitting or fission into smaller fragments.
Facts of Nuclear Fission
Experimental observation suggests the number of facts by which the nuclear fission reaction carried out. In the nuclear fission reaction, a large amount of energy is realized which is considerably greater than any other process. The sum of the mass of the fragments and released neutrons is less than that of the mass of disintegration uranium atom and targeted projectile neutron. In the fission process, the mass defect converted to energy by Einstein relativity equation, E = mc2. For example, 92U235 + 0n1 → 35Br87 + 57La146 + 30n1, the mass defect for the above equation = 2.5.8151310 amu and energy released due to fission reaction = 173.873 MeV.
Nuclear Fission of each heavy atomic nucleus releases 2 to 3 neutrons which under suitable conditions, bombarded fresh nucleus of atoms, splitting to produce more neutrons. Therefore, the chain reaction of splitting going through the emission of a large amount of energy. Uranium-235 is split by slow (thermal) neutrons and fast neutrons in the nuclear fission process. With fast neutrons, uranium-238 suffers nuclear fission to a small extent and the product nuclei differ in mass numbers by a large margin. During the fission process, U-235, the elements formed the fragments belong to two groups, one has a mass number near 140 and the other near about 95. The radioactive isotope uranium-233 obtained from thorium by neutron irradiation suffers nuclear fission like plutonium yielding a considerable amount of energy.
The atomic bomb making on bombarding U-235 with neutrons, for every fission process produced approximately 200 MeV energy. The process yield 3 neutrons that attacked the fresh uranium-235 for fission. In this way, at every stage, the energy output is multiplied by two. The chain would be continued when the peace of U-235 is large enough and secondary neutrons produced to find the fresh targets. If we use a small piece of U-235, the produced neutrons will be escaped and the chain will be break up. Therefore, there is a limiting or critical size of the target for the production of energy by chain propagation. If the size is below the critical size, there will be no explosion and the fission process is safe but for large species from which the secondary neutron cannot escape causes an explosion.
1 Kg of pure uranium-235 produced 2.2 × 107 KWH energy within 10-6 sec as heat in the uranium from which the fission product cannot escape. The atomic bomb making by nuclear fission produces a tremendous explosion resulting in a violent blast with an intense temperature of 107 °K with dangerous radioactive radiation. The first effective bomb, called “lean boy” was released on Hiroshima on Japan at 8:11 A.M. on August 5, 1945, from an altitude of 31600 feet. The effects and pollution of the bomb known to everyone human being now.
The longer the chain propagation in the nuclear fission process the greater will be the explosive power of an atom bomb. In such cases, the energy is very large which cannot be used for any peaceful purpose for mankind. The useful application of nuclear fission energy going through the control of the propagation of the chain. The process is achieved in a nuclear reactor or atomic pile. The nuclear fuels (U or Pu) with other materials are acted as moderators to enable the proper control of the self-sustaining chain reaction. In such nuclear fission process not only avoided the explosive tendencies but the reactor supply slow or fast neutrons, producing radioactive nuclides, liberating specific heat energy that could be used to drive a turbine for electric power generation.
Nuclear Fusion and Fission
All the useable energy has come from the basic physical or chemical process by burning carbon based materials like wood, coal, and sun or from renewable energy sources like sun, wind, and water. Nuclear fusion and fission reaction also produced a large amount of energy but the application of produced energy is different. In the fission process, the heavy nucleus of a radioactive atom split into lower nuclei to produces a large amount of energy but in a nuclear fusion reaction, two light nuclei combine by releasing vast amounts of energy. The fission process used in the nuclear reactor for generating electricity for mankind but the fusion reaction does not utilize to produce electric power because the reaction is not easily controlled.