In an effort to catch "dirty" radioactive bombs and weapons of terrorists, the U.S. government has in recent years installed highly sensitive radiation sensors at all of its land, sea and air points of entry.

Ten days ago they caught Don Tracey's radioactive blood.

In what one U.S. Customs and Border Protection officer says is now "a daily occurrence," American border agents are pulling aside people who have undergone nuclear medical procedures such as stress tests and radiation treatments. You could say they're now catching Canadians with glowing hearts.

They're also catching everything from glazed plates made with naturally radioactive earth to industrial radiation sources used in surveying equipment.

The discoveries come as a result of the U.S. installing "radiation portal monitors" so sensitive that they can detect radiation emanating from the luminescent dial of an old Second World War military compass.

Most people crossing the border are oblivious to the array of equipment they have to pass through. But now Tracey knows some of it scans for low-level radiation.

Tracey and his wife Yuki were on their way to Lake Samish, Wash., on their motorcycle on July 25 when they were stopped at the Aldergrove border crossing. Tracey said an officer almost immediately asked him if he had undergone a medical treatment in the U.S.

"I thought that was a bit odd, and I told him no," Tracey said.

The pair were then taken aside, where another officer asked him the same question. That's when Tracey, 65, remembered he'd undergone a stress test using the radioactive isotope thorium at Lions Gate Hospital two weeks earlier.