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## Secular equilibriumIn nuclear physics, ## Additional recommended knowledge## Secular equilibrium in radioactive decaySecular equilibrium can only occur in a radioactive decay chain if the half-life of the daughter radionuclide B is much shorter than the half-life of the parent radionuclide A. In such a situation, the decay rate of A, and hence the production rate of B, is approximately constant, because the half-life of A is very long compared to the timescales being considered. The quantity of radionuclide B builds up until the number of B atoms decaying per unit time becomes equal to the number being produced per unit time; the quantity of radionuclide B then reaches a constant, The quantity of radionuclide B when secular equilibrium is reached is determined by the quantity of its parent A and the half-lives of the two radionuclide. This can be seen from the time rate of change of the number of atoms of radionuclide B: where λ Secular equilibrium occurs when Over long enough times, comparable to the half-life of radionuclide A, the secular equilibrium is only approximate; N - ,
and the "equilibrium" quantity of radionuclide B declines in turn. For times short compared to the half-life of A, and the exponential can be approximated as 1. ## ReferencesIUPAC definition EPA definition [1]Radioacktiva |

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Secular_equilibrium". A list of authors is available in Wikipedia. |