▪ I. fission, n.
(ˈfɪʃən)
[ad. L. fissiōn-em, n. of action f. findĕre to split.]
1. The action of splitting or dividing into pieces.
| 1865 Pop. Sc. Rev. Jan. 177 Fission or the separation of cuttings is used to perpetuate the same variety. |
2. spec. in
Biol. The division of a cell or organism into new cells or organisms, as a mode of reproduction.
| 1841–71 T. R. Jones Anim. Kingd. 49 In some elongated species the fission is effected in a longitudinal direction. 1846 Patterson Zool. 38 A Medusa may actually be generated..by fertile ova, by gemmation, and by spontaneous fission. |
| transf. 1883 Abbott Alphabet, Vau had the singular fate of generating four other letters by a sort of spontaneous fission. 1950 R. A. Knox Enthusiasm 68 Yet the schism went on; and, as is the way of schisms, propagated itself by fission. |
3. spec. in
Astr. The breaking up of one star into two others, as postulated in one theory of the origin of binary stars.
| 1919 J. H. Jeans Probl. Cosmogony & Stellar Dynamics xi. 246 (heading) The evolution of binary and multiple stars: the process of fission. 1924 H. Dingle Mod. Astrophysics xv. 236 A binary star may originate in the division, or fission, of a single star which, by its contraction, acquires such a high rotational velocity as to become unstable. 1957 A. W. Titherley Orig. Solar Syst. ii. 9 As Algol and most other eclipsing binaries have very short periods..it cannot be doubted that before fission the dense central core had previously become elongated. 1964 R. H. Baker Astron. (ed. 8) xiv. 421 The fission theory..was favored in former times, and some recent efforts have been made to revive it in amended form. |
4. spec. in
Nuclear Physics. The splitting, either spontaneously or under the impact of another particle, of a heavy nucleus into two (very rarely three or more) approximately equal parts, with resulting release of large amounts of energy.
| 1939 Meitner & Frisch in Nature 11 Feb. 239/2 By bombarding thorium with neutrons, activities are obtained which have been ascribed to radium and actinium isotopes. Some of these periods are approximately equal to periods of barium and lanthanum isotopes resulting from the bombardment of uranium. We should..like to suggest that these periods are due to a ‘fission’ of thorium. Ibid. 240/1 ‘Fission’ of the nucleus. 1942 J. D. Stranathan ‘Particles’ of Mod. Physics xi. 443 Neutron bombardment of uranium causes the uranium nucleus to split into two parts not far different in mass. This approximately equal splitting is called fission. 1947 J. Hayward Prose Lit. since 1939 17 It remains to be seen whether man's discovery and immediate abuse of the cataclysmic energy released by atomic fission will fortify or weaken his transcendental aspirations and noumenal gropings. 1957 Encycl. Brit. II. 648/2 The fission of one pound of uranium yields about 10,000,000 kw. hr... To produce this same amount of energy would require the combustion of 3,000,000 lb. of coal. 1965 J. S. Strettan Ionizing Radiations vii. 123 If the neutrons produced by one fission are slowed down sufficiently before they meet the next U235 atom, fission will continue and the chain reaction will be established. 1967 Roy & Nigam Nuclear Physics v. 162 Most heavy nuclides undergo spontaneous fission in competition with the emission of an a-particle. |
5. attrib. and
Comb., as (sense 4)
fission bomb,
fission chain reaction,
fission fragment,
-fusion-fission,
fission neutron,
fission process,
fission product,
fission reactor,
fission spectrum,
fission yield.
| 1941 in H. D. Smyth Gen. Acct. Devel. Atomic Energy Mil. Purposes (1945) iv. 42 A fission bomb of superlatively destructive power will result from bringing quickly together a sufficient mass of element U-235. 1957 Encycl. Brit. II. 651/1 In a fission bomb the uranium or plutonium explode simultaneously if a sufficient amount of material is assembled. |
| 1950 F. Gaynor Encycl. Atomic Energy 37 The fission chain reaction occurring in the atomic bomb, in which a neutron is captured by a uranium nucleus. |
| 1950 Amer. Speech XXV. 26 The process of fission has..created such phrases as..fission spectrum, fission yield, fission fragments. 1965 Gloss. Atomic Terms (H.M.S.O.) 25 Fission fragments, freshly produced fission products before they have been slowed down by nearby matter. |
| 1955 Sci. Amer. Aug. 46/3 Speculation about the ‘fission-fusion-fission’ bomb..was indirectly confirmed last month by Atomic Energy Commissioner Willard F. Libby. This weapon is said to consist of a fission bomb which triggers a thermonuclear reaction which in turn causes ordinary uranium (238) to fission. In a speech at the University of Chicago, Libby mentioned ‘a nuclear explosion releasing 10 megatons of fission energy’. 1966 Observer 15 May 2/5 ‘Fission-fusion-fission’ means a three-stage bomb with a uranium or fission trigger, a hydrogen or fusion intermediate stage..and an outer case of ‘natural’ uranium 238. |
| 1956 A. H. Compton Atomic Quest 26 A means of slowing down the fission neutrons. |
| 1939 Meitner & Frisch in Nature 11 Feb. 239/2 It seems..possible that the uranium nucleus has only small stability of form, and may, after neutron capture, divide itself into two nuclei of roughly equal size... The whole ‘fission’ process can..be described in an essentially classical way. |
| 1939 Nature 13 May Suppl. 794 (heading) Decay curves of uranium and thorium fission products. 1955 Sci. News Let. 5 Mar. 147/1 Fission products are atoms of chemical elements newly formed, during the explosion, out of the fragments of uranium and plutonium atoms. |
| 1948 Physics Abstr. 488 Nuclear fission reactors. 1955 Newsweek 1 Aug. 11/2 A new type reactor seems to be under development in which fusion—the H-bomb principle—supplements the energy provided by the usual fission reactor. |
| 1960 Gloss. Atomic Terms (H.M.S.O.) 25 Fission spectrum, the wide range of elements and isotopes formed in fission is called the fission spectrum. Up to 35 elements may be formed [etc.]. Ibid., Fission yield, the fraction of fissions giving rise to one particular group of fission products all having the same mass number. |
▪ II. fission, v. (
ˈfɪʃən)
[f. the n.] 1. intr. To undergo fission; to split or divide into a small number of parts comparable in size.
| 1929 J. H. Jeans Universe around Us 226 The development of the hypothetical chaos has now been traced through five generations of astronomical bodies, chaos—nebulae—stars—binary systems—sub-systems, to which a sixth generation must be added if the stars of the sub-system happen to fission further. 1971 Sci. Amer. June 87/1 The bubble is pinched at the waist and finally fissions into two bubbles. |
2. trans. and intr. In
Nuclear Physics: to split or break up into fission products; to cause (a nucleus) to undergo fission.
| 1947 Sci. News Let. 20 Sept. 181 (heading) Lighter elements fissioned. 1949 Nucleonics May 6/1 The isotope uranium-235..is the only naturally occurring substance that can be fissioned with most of the neutrons available within a pile. 1950 A. C. Clarke Interplanetary Flight 84 This is necessary to maintain the chain reaction in normal uranium, which is fissioned only by slow-moving (‘thermal’) neutrons. 1955 Wall St. Jrnl. 24 Feb. 5/2 Uranium atoms would fission in the graphite core of the proposed reactor. 1965 G. R. Keepin Physics Nucl. Kinetics i. 3 We shall adopt the convention recommended by the American Nuclear Society. Thus ‘fissile’ will herein refer to those heavy nuclides which can be fissioned by thermal neutrons. 1967 W. E. Meyerhof Elem. Nucl. Physics v. 219 Another process can start when U237 can be created with sufficient excitation energy to fission. |
Hence
ˈfissioning vbl. n. and ppl. a.| 1955 Sci. News Let. 23 July 51/3 Fissioning of uranium 235 atoms in solution provides the gamma rays and neutrons for medical treatment and other research. 1965 G. R. Keepin Physics Nucl. Kinetics ii. 13 We find that the mass of a fissioning U236 nucleus is greater than the total mass of its..fission products. |