
1) Atom splitting
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https://www.crosswordclues.com/clue/nuclear-fission

fission. Compare with nuclear fusion. Splitting of a nucleus into two smaller nuclei and neutrons. The smaller nuclei have higher binding energy than the original nucleus, and fission results in the release of energy.
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http://antoine.frostburg.edu/chem/senese/101/glossary/n.shtml

In nuclear physics and nuclear chemistry, nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei). The fission process often produces free neutrons and photons (in the form of gamma rays), and releases a very large amount of energy even by the energetic ...
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http://en.wikipedia.org/wiki/Nuclear_fission

The splitting of an atom into two smaller atoms of nearly equal mass by breaking up of the original atom?s nucleus
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http://jot101.com/2015/05/a-z-of-science-fiction-words/

subdivision of a heavy atomic nucleus, such as that of uranium or plutonium, into two fragments of roughly equal mass. The process is accompanied by ... [17 related articles]
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http://www.britannica.com/eb/a-z/n/61

The process in which a heavy nucleus splits into nuclei of intermediate masses and one or more protons are emitted.
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http://www.chemistry-dictionary.com/definition/nuclear+fission.php

nuclear reaction initiated by neutrons, gamma radiation or charged particles which results in the division of the atomic nucleus in two fragments (more rarely three) whose mass is of the same order of magnitude and which is attended by emission of neutrons, gamma radiation and a high level of energy NOTE - For certain radionuclides, the nuclear fis...
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http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=393-12-38

the division of a heavy nucleus into two (or rarely, more) parts, usually accompanied by the emission of neutrons and energy. Fission may occur spontaneously or as a result of the absorption of a neutron or photon
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http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=881-03-54

The process in which a heavy nucleus splits into nuclei of intermediate masses and one or more protons are emitted.
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http://www.encyclo.co.uk/local/20728

Nuclear reaction in which the nucleus of a heavy atom such as uranium or plutonium is split into two approximately equal parts by a neutron, charged particle, or photon. ... (12 Dec 1998) ...
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http://www.encyclo.co.uk/local/20973

The splitting of uranium isotopes to produce heat, which is then harnessed to produce electricity.
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http://www.encyclo.co.uk/local/21291

The division of the nuclei of isotopes of certain heavy elements, such as uranium and plutonium, effected by bombardment with neutrons. Nuclear fission causes the release of energy, additional neutrons, and an enormous quantity of heat. Nuclear fission is used in nuclear power plants and nuclear weapons. A by product of nuclear fission is toxic ra...
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http://www.encyclo.co.uk/local/22291

Occurs when the atomic nucleus splits into two or more smaller nuclei plus some by-products. These by-products include free neutrons and photons (usually gamma rays). Fission releases substantial amounts of energy (the nuclear binding energy ). The neutrons released by the fission process may collide with other nuclei causing them in turn to underg...
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http://www.mpoweruk.com/glossary.htm

is the breakup of heavy nuceli into two medium mass nuclei with an accompanying release of energy. This form of nuclear instability ultimately limits the extent to which heavy nuclei can be synthesised. It places an upper limits on the atomic number (A) of nuclei produced by the r-process.
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http://www.sheffield.ac.uk/polopoly_fs/1.14548!/file/glossary.pdf

it is the process whereby an atomic nucleus breaks up with the emissions of several neutrons.
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http://www.vidyagyaan.com/general-knowledge/science/glossary-of-physics-ter

the process of splitting a large atom into two or more smaller atoms, releasing large amounts of energy
Found on
https://sciencetrek.org/sciencetrek/topics/nuclear_energy/glossary.cfm

fission (def. 2).
Found on
https://www.infoplease.com/dictionary/nuclear-fission
No exact match found.