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Fission is a nuclear reaction or radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei and often other particles. The fission process often produces gamma rays and releases a very large amount of energy
A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as fission and fusion. Some early evidence for nuclear fission was the formation of a short-lived radioisotope of barium which was isolated from neutron irradiated uranium ( 139 Ba, with a half-life of 83 minutes and 140 Ba, with a half-life of 12.8 ...
About 6 MeV of the fission-input energy is supplied by the simple binding of an extra neutron to the heavy nucleus via the strong force; however, in many fissionable isotopes, this amount of energy is not enough for fission. Uranium-238, for example, has a near-zero fission cross section for neutrons of less than 1 MeV energy.
A numerical measure of a critical mass depends on the effective neutron multiplication factor k, the average number of neutrons released per fission event that go on to cause another fission event rather than being absorbed or leaving the material. A subcritical mass is a mass that does not have the ability to sustain a fission chain reaction ...
239 Pu has a higher probability for fission than 235 U and a larger number of neutrons produced per fission event, so it has a smaller critical mass. [6] Pure 239 Pu also has a reasonably low rate of neutron emission due to spontaneous fission (10 fission/s·kg), making it feasible to assemble a mass that is highly supercritical before a ...
Half-life (symbol t ½) is the time required for a quantity (of substance) to reduce to half of its initial value.The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive.
Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.. In sufficiently massive stars, the nucleosynthesis by fusion of lighter elements into heavier ones occurs during sequential hydrostatic burning processes called helium burning, carbon burning, oxygen burning, and silicon burning, in which the byproducts of one nuclear fuel become, after ...
In their second publication on nuclear fission in February 1939, Hahn and Strassmann used the term uranspaltung (uranium fission) for the first time and predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction. [6]