radioactivity
radioactivity a`di*o*ac*tiv"i*ty (r[=a]`d[i^]*[-o]*[a^]k*t[i^]v"[i^]*t[y^]), n. (Physics) a form of instability which is a property of the atomic nuclei of certain isotopes, which causes a spontaneous change in the structure of the nucleus, accompanied by emission of energetic radiation. The radiation emitted is usually sufficient to cause ionization in matter through which it passes, and is therefore called {ionizing radiation}. The radiation emitted by most radioactive substances is one of three types: {alpha rays}, {beta rays}, or {gamma rays}. Some chemical elements have no stable isotopes, and these are referred to as radioactive elements, and the element itself is said to possess radioactivity.

Note: The changes in radioactive nuclei which cause radiation in most cases cause the chemical identity of the nucleus itself to change, as when tritium (an isotope of hydrogen) emits a beta ray and converts to helium. The radioactive decay process is a first-order reaction, and the rate of decay of a particular isotope can therefore be expressed as the {half life} of the isotope, which is the time it takes for one half of the remaining undecayed isotope to decay, and is a constant independent of the proportion of original material which has already decayed. The half life of tritium, for example, is 12.3 years. [PJC]


The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

  • radioactivity — radioactivity. См. радиоактивность. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Radioactivity — Radioactivity. См. Радиоактивность. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • Radioactivity — См. Радиоактивность Термины атомной энергетики. Концерн Росэнергоатом, 2010 …   Термины атомной энергетики

  • radioactivity — (n.) 1899, from RADIOACTIVE (Cf. radioactive) + ITY (Cf. ity) …   Etymology dictionary

  • radioactivity — ► NOUN 1) the emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei. 2) radioactive particles …   English terms dictionary

  • radioactivity — /ray dee oh ak tiv i tee/, n. Physics, Chem. the phenomenon, exhibited by and being a property of certain elements, of spontaneously emitting radiation resulting from changes in the nuclei of atoms of the element. Also called activity. [1895… …   Universalium

  • radioactivity — noun … OF RADIOACTIVITY ▪ level ▪ The soil contains 30 times the acceptable level of radioactivity. VERB + RADIOACTIVITY ▪ produce, release ▪ the amount of radioactivity released b …   Collocations dictionary

  • radioactivity — n. 1) to emit, generate, produce radioactivity 2) (a) dangerous (level of) radioactivity * * * generate produce radioactivity (a) dangerous (level of) radioactivity to emit …   Combinatory dictionary

  • radioactivity — Synonyms and related words: activity, artificial radioactivity, contamination, curiage, decontamination, fallout, half life, natural radioactivity, nuclear radiation, radiant energy, radiation, radioactive radiation, radiocarbon dating,… …   Moby Thesaurus

  • radioactivity — ra|di|o|ac|tiv|i|ty [ˌreıdiəuækˈtıvıti US diou ] n [U] the sending out of ↑radiation (=a form of energy) when the ↑nucleus (=central part) of an atom has broken apart ▪ the discovery of radioactivity ▪ high levels of radioactivity …   Dictionary of contemporary English

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