Nuclear fission of heavy elements was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch. Frisch named the process by analogy with biological fission of living cells. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). In order for fission to produce energy, the total binding energy of the resulting elements must be more negative (greater binding energy) than that of the starting element.
Hence, fission is a form of elemental transmutation.
The by-products include free neutrons, photons usually in the form gamma rays, and other nuclear fragments such as beta particles and alpha particles.
Fission of heavy elements is an exothermic reaction and can release substantial amounts of useful energy both as gamma rays and as kinetic energy of the fragments (heating the bulk material where fission takes place).
Nuclear fission produces energy for nuclear power and to drive explosion of nuclear weapons.
In physics, nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus.
It is accompanied by the release or absorption of energy depending on the masses of the nuclei involved.
Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei and therefore are the most stable.
The fusion of two nuclei lighter than iron or nickel generally releases energy while the fusion of nuclei heavier than iron or nickel absorbs energy; vice-versa for the reverse process, nuclear fission.
Nuclear fusion of light elements releases the energy that causes stars to shine and hydrogen bombs to explode.
Nuclear fusion of heavy elements (absorbing energy) occurs in the extremely high-energy conditions of supernova explosions.
Nuclear fusion in stars and supernovae is the primary process by which new natural elements are created.
It is this reaction that is harnessed in fusion power.
It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen.
Difference between Nuclear fission and Nuclear fusion
|Nuclear Fission||Nuclear Fusion|
|When a heavy nucleus like U-235 splits up into nearly two equal parts by the bombardment of slow-moving neutrons considerable amount of energy is released.||When two or more lighter atoms of hydrogen or protons are fused into heavier atom, a large amount of energy is released.|
|The principle behind atom bomb is Nuclear fission.||The principle behind the hydrogen bomb is nuclear fusion.|
|In this reaction, 200 MeV of energy is released per fission.||In this reaction 25.71 MeV of energy is released.|
|Energy released per nucleon is less.||The energy released per nucleons is more.|
|Particles involved are neutrons||Particles involved are protons.|
|Fission takes place at room temperature.||Fusion takes place only at very high temperature and high pressure.|
|Fission produces radioactive elements like Barium and Krypton which are harmful (radioactive)||The products of fusion are harmless (not radioactive)|