TECHNETIUM-99M: A radioactive isotope used in at least 20 million medical scans in the United States each year and which has been at the center of controversy because of the shutdown of a 50-year-old nuclear reactor in Canada.

Chalk River Laboratories produces as much as 80% of the world’s supply of the radiopharmaceutical, which is used to diagnose and treat a range of diseases. In November 2007, the reactor was closed after the Canadian Nuclear Safety Commission discovered that emergency power systems were not connected to cooling pumps. The reactor was expected to resume production in early to mid-January 2008. Yet as hospitals throughout North America began to feel the squeeze—delaying tests or finding more complicated alternatives—the Canadian government took surprising action. Overriding the nuclear watchdog, the government passed emergency legislation on December 12 to reopen the reactor for 120 days.

Once production resumed, hospitals were likely to wait as many as two to three weeks for replenishments, according to Alexander McEwan, president of the Society of Nuclear Medicine, which has pressed before for the creation of an American source of the radiopharmaceutical. “This will renew the conversation,” he says. There’s likely to be no end to critics’ conversation in Canada about the government’s decision to choose patients worldwide over the lives of Canadians within fallout range of Chalk River.