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radioactive decay

radioactive decay Process by which a radioactive isotope (radioisotope) loses subatomic particles from its nucleus and so becomes a different element. The disintegration of the nuclei occurs with the emission of alpha particles (helium nuclei) or beta particles (electrons), often accompanied by gamma radiation. The two processes of alpha or beta decay cause the radioisotope to transform into a different atom. Alpha decay results in the nucleus losing two protons and two neutrons; beta decay occurs when a neutron changes into a proton, with an electron (beta particle) emitted in the process. Thus, the atomic number (total protons in the nucleus if an atom) changes in both types of decay, and an isotope of another element is produced that might also be radioactive. In a large collection of atoms, there is a characteristic time (the half-life) after which one-half of the total number of nuclei would have decayed. This time varies from millionths of a second to millions of years, depending on the isotope concerned. The activity of any radioactive sample decreases exponentially with time. See also carbon dating

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radioactive decay

radioactive decay Process by which a radioactive ‘parent’ element loses elementary particles from its nucleus and in doing so becomes a stable ‘daughter’ element. The rate of decay is constant for a given element and is a very precise and accurate device for the measurement of geologic time. See also DECAY CONSTANT; and DECAY CURVE.

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