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Radioactivity in biological research
Radioactivity can be used in life sciences as a radiolabel to easily visualise components or target molecules in a biological system. Radionuclei are synthesised in particle accelerators and have short half-lives, giving them high maximum theoretical specific activities. This lowers the detection time compared to radionuclei with longer half-lives, such as carbon-14. In some applications they have been substituted by fluorescent dyes.
Additional recommended knowledge
Examples of radionuclei
In a scintillation counter, the H-3 energy range window is between channel 5–360; C-14, S-35 and P-33 are in the window of 361–660; and P-32 is in the window of 661–1024.
A vial of radiolabel has a "total activity". Taking as an example γ32P ATP, from the catalogues of the two major suppliers, Perkin elmer NEG502H500UC  or GE AA0068-500UCI , in this case, the total activity is 500 μCi (other typical numbers are 250 μCi or 1 mCi). This is contained in a certain volume, depending on the radioactive concentration, such as 5 or 10 mCi/mL; typical volumes include 50 or 25 μL.
Not all molecules in the solution have a P-32 on the last (i.e., gamma) phosphate: the "specific activity" gives the radioactivity concentration and depends on the radionuclei's half-life. If every molecule were labelled, the maximum theoretical specific activity is obtained that for P-32 is 9131 Ci/mmole. Due to pre-calibration and efficiency issues this number is never seen on a label; the values often found are 800, 3000 and 6000 Ci/mmole. With this number it is possible to calculate the total chemical concentration and the hot-to-cold ratio.
"Calibration date" is the date in which the vial’s activity is the same as on the label. "Pre-calibration" is the when the activity is calibrated in a future date to compensate for the decay occurred during shipping.
Radionuclei used in a biology lab are extremely faint compared to well-known radioactive samples such as uranium. Nevertheless the effects of low doses are mostly unknown so many regulations exist to avoid unnecessary risks, such as skin or internal exposure. Due to the low penetration power and many variables involved it is hard to convert a radioactive concentration to a dose. 1 μCi of P-32 on a square centimetre of skin (through a dead layer of a thickness of 70 μm) gives 7961 rad per hour. Similarly a mammogram gives an exposure of 300 mrem on a larger volume (in the US, the average annual dose is 360 mrem).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radioactivity_in_biological_research". A list of authors is available in Wikipedia.|