Friday, December 14, 2007

Technetium Shortage

The shutdown of a nuclear reactor at Chalk River, Ontario has caused a shortage of an isotope of technetium (Tc-99m) used for medical imaging (see the New York Times article for details). What is technetium, and how is it produced? The following is a quote from the 4th edition of Intermediate Physics for Medicine and Biology (page 497).
The most widely used isotope [for medical imaging] is Tc-99m. As its name suggests, it does not occur naturally on earth, since it has no stable isotopes. We consider it in some detail to show how an isotope is actually used... The isotope is produced in the hospital from the decay of its parent, Mo-99 [molybdenum], which is a fission product of U-235 and can be separated from about 75 other fission products. The Mo-99 decays to Tc-99m.

Technetium is made available to hospitals through a “generator” that was developed at Brookhaven National Laboratories in 1957 and is easily shipped. Isotope Mo-99, which has a half-life of 67 h, is adsorbed on an alumina substrate... As the Mo-99 decays, it becomes pertechnetate (TcO4-). Sterile isotonic eluting solution is introduced under pressure above the alumina and passes through after filtration into an evacuated eluate container. After removal of the technetium, the continued decay of Mo-99 causes the Tc-99m concentration to build up again. A generator lasts about a week.

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