The shutdown of a Canadian nuclear reactor that produces radioisotopes is causing delays in medical diagnoses and treatments, but nuclear medicine researchers seem unaffected so far.

In mid-November, Atomic Energy of Canada Limited (AECL) shut down its National Research Universal reactor in Chalk River, Ontario for what was supposed to be five days of routine maintenance. But the reactor remains powered down while engineers retool the water pump's emergency power supply. The reactor is North America's sole producer of molybdenum-99, the raw material for technetium-99, the most widely used isotope for diagnosing disease.

"The clinical sciences are very much restricted," Stanford radiologist Michael Goris told The Scientist. Goris said, though, that radiological research has not been seriously affected because the isotope supply has only been interrupted for a brief period. "In research terms, two weeks is a short time," he said.

The reactor's prolonged closure has caused a shortage of technetium-99 in hospitals, where it is used to diagnose cancers, heart and kidney problems among other ailments. The reactor supplies 50-80 percent of the world's molybdenum-99, according to the The New York Times.

Technetium-99 has a half-life of only six hours, which makes it an ideally short lived diagnostic isotope for medical procedures but means that supplies must be constantly replenished.

AECL has estimated that the reactor will not reopen until January, 2008.