Editing Specific activity (section)

{{Short description|Activity per unit mass of a radionuclide}}
{{About|specific activity radioactivity|the use in biochemistry|Enzyme assay#Specific activity}}
{{technical|date=January 2014}}
{{Infobox physical quantity
| name = Activity
| image = Radium 226 radiation source 1.jpg
| caption = Ra 226 radiation source. Activity 3300 Bq (3.3 kBq)
| unit = [[becquerel]]
| otherunits = [[Rutherford (unit)|rutherford]], [[Curie (unit)|curie]]	
| symbols = ''A''
| baseunits = s<sup>−1</sup>
| dimension =
| extensive =
| intensive =
| derivations =
}}
{{Infobox physical quantity
| name = Specific activity
| image = 
| caption = 
| unit = [[becquerel]] per [[kilogram]]
| otherunits = [[Rutherford (unit)|rutherford]] per [[gram]], [[Curie (unit)|curie]] per gram
| symbols = ''a''
| baseunits = s<sup>−1</sup>⋅kg<sup>−1</sup>
| dimension =
| extensive =
| intensive =
| derivations =
}}
'''Specific activity''' (symbol ''a'') is the activity [[per unit mass]] of a [[radionuclide]] and is a physical property of that radionuclide.<ref name="BreemanJong2003">{{cite journal |last1=Breeman |first1=Wouter A. P. |last2=Jong |first2=Marion |last3=Visser |first3=Theo J. |last4=Erion |first4=Jack L. |last5=Krenning |first5=Eric P. |title=Optimising conditions for radiolabelling of DOTA-peptides with <sup>90</sup>Y, <sup>111</sup>In and <sup>177</sup>Lu at high specific activities |journal=European Journal of Nuclear Medicine and Molecular Imaging |volume=30 |issue=6 |year=2003 |pages=917–920 |issn=1619-7070 |doi=10.1007/s00259-003-1142-0 |pmid=12677301|s2cid=9652140 }}</ref><ref name="de GoeijBonardi2005">{{cite journal |last1=de Goeij |first1=J. J. M. |last2=Bonardi |first2=M. L. |title=How do we define the concepts specific activity, radioactive concentration, carrier, carrier-free and no-carrier-added? |journal=Journal of Radioanalytical and Nuclear Chemistry |volume=263 |issue=1 |year=2005 |pages=13–18 |issn=0236-5731 |doi=10.1007/s10967-005-0004-6|s2cid=97433328 }}</ref>
It is usually given in units of becquerel per kilogram (Bq/kg), but another commonly used unit of specific activity is the curie per gram (Ci/g).

In the context of [[radioactivity]], activity or total activity (symbol ''A'') is a [[physical quantity]] defined as the number of radioactive transformations per second that occur in a particular [[radionuclide]].<ref>{{cite journal |title=SI units for ionizing radiation: becquerel |journal=Resolutions of the 15th CGPM |date=1975 |issue=Resolution 8 |access-date=3 July 2015 |url=http://www.bipm.org/en/CGPM/db/15/8/}}</ref> The unit of activity is the ''[[becquerel]]'' (symbol Bq), which is defined equivalent to [[reciprocal second]]s (symbol s<sup>−1</sup>). The older, non-SI unit of activity is the [[Curie (unit)|''curie'']] (Ci), which is {{val|3.7|e=10}} radioactive decays per second. Another unit of activity is the [[Rutherford (unit)|''rutherford'']], which is defined as {{val|1|e=6}} radioactive decays per second.

The specific activity should not be confused with level of exposure to [[ionizing radiation]] and thus the exposure or [[absorbed dose]], which is the quantity important in assessing the effects of ionizing radiation on humans.

Since the probability of [[radioactive decay]] for a given radionuclide within a set time interval is fixed (with some slight exceptions, see [[Radioactive decay#Changing rates|changing decay rates]]), the number of decays that occur in a given time of a given mass (and hence a specific number of atoms) of that radionuclide is also a fixed (ignoring statistical fluctuations).