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== | ||
| − | The [[ | + | The [[Activity (radioactivity)|activity]] ''A'' of a sample is defined as |
| − | : | + | :''A'' = d''N''/d''t'' = ''λN'' |
| − | where ''N'' is the number of radioactive atoms in the sample and '' | + | 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'' = ''N''<sub>A</sub> and so ''A''<sub>m</sub> = ''λN''<sub>A</sub>. One mole of atoms has a mass equal to the [[molar mass]] of the nuclide, ''M'', so the specific activity is ''λN''<sub>A</sub>/''M''. Equivalent definitions of the specific activity are ''λ''/''m''<sub>a</sub> (where ''m''<sub>a</sub> is the [[atomic mass]] of the nuclide) or ''λ''/''A''<sub>r</sub>''m''<sub>u</sub> (where ''m''<sub>u</sub> is the [[atomic mass constant]] and ''A''<sub>r</sub> is the [[relative atomic mass]] of the nuclide). | ||
==References== | ==References== | ||
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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