Radioactive tracers are molecules that contain at least one radioactive atom in their structure, to facilitate detection and measurement. Radioactive atoms disintegrate spontaneously at a typical rate, giving off radiation that can be detected by several techniques and instruments.
Tracers are typically used to monitor biochemical and physiological processes. The rate of absorption, transport and metabolism of a radioactively-labeled herbicide can be followed by sampling plant tissue from different locations after different periods of time and 'counting' the radiation levels.
C-14, P-32 and H-3 are among the most commonly used radioisotopes. All three isotopes emit beta radiation, each with a different energy. The radiation can be monitored with a beta counter, after the sample has been solubilized in scintillation liquid. A Sample Oxidizer can be used to combust raw tissue samples tagged with either tritium or C-14, and solubilize the radioactive compounds in the scintillation liquid.
Proteins are frequently labeled with a radioisotope to facilitate their identification and quantitation following chromatographic separation. An image of the distribution of labeled products on a gel, following electrophoresis, can be transferred to an X-ray film by pressing the two together in a cassette for several hours. The film is next developed in a X-ray Film Processor, and analyzed with a suitable densitometer.
Alternatively the film can be replaced by a special Imaging Plate. The material coating such a plate responds to beta particles, emitted by the labeled gel, creating a latent image of the spot distribution on the gel. This latent image is next developed by an 'Imager' such as the FLA-5000.
I-125 is also widely used as a tracer. The gamma radiation emitted can be measured with a Gamma Counter.
|Instrument||Make & Model|
|Beta-Counter||Packard 1900 TR Scintillation Counter|
|Gamma-Counter||Packard Cobra-II Auto gamma counter|
|Radioisotope and Fluorescence Imager||Fuji FLA-5000|
|X-ray Film Processor||Agfa Curix 60|
|Sample Oxidizer||Packard 307 sample Oxidizer|