Difference between revisions of "Specific activity"
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| − | '''Specific activity''' is the [[Radioactivity|radioactive]] [[activity]] of a sample per unit [[mass]]. In [[SI unit]]s, it is measured in [[becquerel]]s per [[kilogram]] ( | + | '''Specific activity''' is the [[Radioactivity|radioactive]] [[activity]] of a sample per unit [[mass]]. In [[SI unit]]s, it is measured in [[becquerel]]s per [[kilogram]] ({{nowrap|Bq kg<sup>−1</sup>}}). |
==Definition== | ==Definition== | ||
Latest revision as of 20:23, 23 May 2010
Specific activity is the radioactive activity of a sample per unit mass. In SI units, it is measured in becquerels per kilogram (Bq kg−1).
Definition
The activity A of a sample is defined as
- A = dN/dt = λN
where N is the number of radioactive atoms in the sample and λ is the decay constant. For a sample of mass m, the specific activity is simply A/m.
A specific activity can also be defined for a particular nuclide, by assuming a sample consisting solely of the nuclide in question. For one mole of atoms, N = NA and so Am = λNA. One mole of atoms has a mass equal to the molar mass of the nuclide, M, so the specific activity is λNA/M. Equivalent definitions of the specific activity are λ/ma (where ma is the atomic mass of the nuclide) or λ/Armu (where mu is the atomic mass constant and Ar is the relative atomic mass of the nuclide).
References
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