GC: n
CT: Nuclear fission is a nuclear reaction in which a heavy nucleus (such as uranium) splits into two lighter nuclei (and possible some other radioactive particles as well).
In such radioactive heavy nuclei, the balance between the strong nuclear force attractive force and the electrostatic repulsive force can be knocked out of equilibrium, by the introduction of energy in the form of an absorbed neutron or photon, the nucleus oscillates in an attempt to regain equilibrium until the electrostatic force gains more power than the shorter-distanced nuclear force, at which point the nucleus splits apart, releasing energy as it does so.
S: ABOUT – http://physics.about.com/od/glossary/g/nuclearfission.htm (last access: 20 November 2015)
N: 1. nuclear (adj): 1846, “of or like the nucleus of a cell,” from nucleus + -ar, probably by influence of French nucléaire. Use in atomic physics is from 1914; of weapons, from 1945. Hence nuclear physics (1933), nuclear energy (1941), nuclear war (1954). Alternative adjective nucleal is recorded from 1840.
fission (n): 1819, “division of a cell or organism,” from Latin fissionem (nominative fissio) “a breaking up, cleaving,” from past participle stem of findere “to split”. Cognate with Old English bitan “to bite.” Nuclear physics sense is 1939. As a verb, from 1929.
2. Fission is the splitting of an atomic nucleus resulting in the release of large amounts of energy—called also nuclear fission.
3. The discovery of fission: in 1934, physicist Enrico Fermi conducted experiments in Rome that showed neutrons could split many kinds of atoms. The results surprised even Fermi himself. When he bombarded uranium with neutrons, he did not get the elements he expected. The elements were much lighter than uranium.
In the fall of 1938, German scientists Otto Hahn and Fritz Strassman fired neutrons from a source containing the elements radium and beryllium into uranium (atomic number 92). They were surprised to find lighter elements, such as barium (atomic number 56), in the leftover materials. These elements had about half the atomic mass of uranium. In previous experiments, the leftover materials were only slightly lighter than uranium.
Hahn and Strassman contacted Lise Meitner in Copenhagen before publicizing their discovery. She was an Austrian colleague who had been forced to flee Nazi Germany. She worked with Niels Bohr and her nephew, Otto R. Frisch. Meitner and Frisch thought the barium and other light elements in the leftover material resulted from the uranium splitting — or fissioning. However, when she added the atomic masses of the fission products, they did not total the uranium’s mass. Meitner used Einstein’s theory to show the lost mass changed to energy. This proved fission occurred and confirmed Einstein’s work.
4. Nuclear fission: term standardized by ISO.
5. Fission: term standardized by ISO and NATO.
S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=nuclear+fission&searchmode=none (last access: 20 November 2015). 2. MW – http://www.merriam-webster.com/medical/fission (last access: 20 November 2015). 3. ENERGY.GOB – http://www.energy.gov/sites/prod/files/The%20History%20of%20Nuclear%20Energy_0.pdf (last access: 20 November 2015). 4 & 5. TERMIUM PLUS – http://goo.gl/xlnFMR (last access: 20 November 2015).
SYN: fission
S: MW – http://www.merriam-webster.com/medical/fission (last access: 20 November 2015)
CR: burial ground, linear accelerator, nuclear energy, nuclear fusion, nuclear reactor, particle accelerator.
