A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators.
Some synthetic radioisotope are extracted from spent nuclear reactor fuel rods, which contain various fission products. For example, it is estimated that up to 1994, about 49,000 TBq (78 metric ton) of technetium was produced in nuclear reactors, which is by far the dominant source of terrestrial technetium. However, only a fraction of the production is used commercially. Other synthetic isotopes are produced in significant quantities by fission but are not yet being reclaimed. Other isotopes are manufactured by neutron irradiation of parent isotopes in a nuclear reactor (for example, Tc-97 can be made by neutron irradiation of Ru-96) or by bombarding parent isotopes with high energy particles from a particle accelerator.
Most synthetic radioisotopes are extremely radioactive and have a short half life. Though a health hazard, radioactive materials have many medical and industrial uses.
The general field of nuclear medicine covers any use of radioisotopes for diagnosis or treatment.
Radioactive tracer compounds are used to observe the function of various organs and body systems. These compounds use a chemical tracer which is attracted to or concentrated by the activity which is being studied. That chemical tracer incorporates a short lived radioactive isotope, usually one which emits a gamma ray which is energetic enough to travel through the body and be captured outside by a gamma camera to map the concentrations. Gamma cameras and other similar detectors are highly efficient, and the tracer compounds are generally very effective at concentrating at the areas of interest, so the total amounts of radioactive material needed are very small.
The metastable nuclear isomer Tc-99m is a Gamma-emitter widely used for medical diagnostics because it has a short half-life of 6 hours, but can be easily made in the hospital using a "technetium-cow".
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