isomern.
/ˈʌɪsəmə/, U.S. /ˈaɪsəmər/ 1. Chemistry. A substance isomeric with another; any one of a number of isomeric compounds.
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isomeride1857
isomer1866
1866 H. E. Roscoe Lessons Elem. Chem. xxxiii. 296 It [sc. ethylene oxide] does not form, like its isomer aldehyde, a crystalline compound with ammonia.
1880 E. Cleminshaw tr. C. A. Wurtz Atomic Theory 295 The notion of atomicity has furnished sure data for the interpretation of isomers.
1885 G. L. Goodale in A. Gray & G. L. Goodale Bot. Text-bk. (ed. 6) II. i. i. 51 The isomers of cellulose are mucilage, gums, and dextrin.
1893 P. Kropotkin in 19th Cent. Aug. 251 Very often such isomeres differ from each other by having different boiling-points.
2. Physics. A nucleus having the same atomic number and mass number but different radioactive properties, as a result of being in a different, long-lived, energy state from which a transition is inhibited; esp. one in a metastable excited state rather than the ground state. Also called nuclear isomer.
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the world > matter > physics > atomic nucleus > radioactive isotope > radioactive nuclide > [noun] > nuclear isomer
isomer1934
1934 Physical Rev. 45 729/2 The introduction of isomers may be of help for the removal of existing contradictions in the estimation of neutronic mass from different nuclear reactions.
1950 S. Glasstone Sourcebk. Atomic Energy x. 278/1 The second class consists of genetically related isomers,..in which the metastable state decays to the ground state with a definite half life.
1955 R. D. Evans Atomic Nucleus iii. 97 Isobaric isotopes with distinguishable nuclear properties are called isomers.
1968 F. B. Morinigo tr. H. von Buttlar Nucl. Physics xiv. 478 If the half-life is larger than 1 msec, the state is called a nuclear isomer (the choice of 1 msec for this definition is arbitrary).
This entry has not yet been fully updated (first published 1900; most recently modified version published online March 2022).
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