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nuclear fission
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nuclear fission
splitting of an atom's nucleus into two equal parts
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Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission refers to either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), and releasing a very large amount of energy, even by the energetic standards of radioactive decay. The two nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes. Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced, in a ternary fission. The smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus.
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nuclear fission
Noun
1. a nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
(synonym) fission
(hypernym) nuclear reaction
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nuclear fission
štěpení
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Nuclear fission
Nucleus is split into (most frequently) two fission fragments. This is the predominant energy production nuclear reaction in all trans-uranic elements since it gives out energy. The energy (E) is the mass defect, or loss of mass, m, (the fragments being of less mass than the original nucleus), times the velocity of light squared: E = mc2. See Special Theory of Relativity .
Spontaneous fission was first discovered by the Russian physicists Flerov and Petrazak in 1940 in uranium. It occurs in nuclides with too many protons, is the simplest form of dynamical instability in nuclei and can be explained in terms of the liquid drop model, as illustrated. A heavy nucleus is in a permanent state of oscillation with a frequency of the order of 10 vibrations/sec. In the course of any one vibration the incompressible nucleus is distorted to a greater or lesser extent, there being a small, but finite, probability that the distortion may become so extreme that a constriction appears between the ends of the elongated nucleus. The mutual electrostatic repulsion of the charges on the two may then be sufficient to overcome the attractive nuclear 'surface tension' forces and to cause the nucleus to rupture. The half-life to such binary fission of uranium-238 is 8 x 1015 years, while that for the competing process of alpha particle emission is 4.5 x 109 years. In any gramme of natural uranium metal there are, on average, 25 spontaneous fissions/hour. The more the number (Z) of mutually repulsive protons the greater the chance of spontaneous fission and so for Z=101 mendelevium the half life is 3.5 hours. This is the basic reason why there is an upper limit to the number of elements in the universe.
Induced fission is when the process is speeded up by hitting the heavy nucleus with a projectile such as a neutron. This fact is utilised in atomic bombs and nuclear reactors here on earth.
Spontaneous fission was first discovered by the Russian physicists Flerov and Petrazak in 1940 in uranium. It occurs in nuclides with too many protons, is the simplest form of dynamical instability in nuclei and can be explained in terms of the liquid drop model, as illustrated. A heavy nucleus is in a permanent state of oscillation with a frequency of the order of 10 vibrations/sec. In the course of any one vibration the incompressible nucleus is distorted to a greater or lesser extent, there being a small, but finite, probability that the distortion may become so extreme that a constriction appears between the ends of the elongated nucleus. The mutual electrostatic repulsion of the charges on the two may then be sufficient to overcome the attractive nuclear 'surface tension' forces and to cause the nucleus to rupture. The half-life to such binary fission of uranium-238 is 8 x 1015 years, while that for the competing process of alpha particle emission is 4.5 x 109 years. In any gramme of natural uranium metal there are, on average, 25 spontaneous fissions/hour. The more the number (Z) of mutually repulsive protons the greater the chance of spontaneous fission and so for Z=101 mendelevium the half life is 3.5 hours. This is the basic reason why there is an upper limit to the number of elements in the universe.
Induced fission is when the process is speeded up by hitting the heavy nucleus with a projectile such as a neutron. This fact is utilised in atomic bombs and nuclear reactors here on earth.
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