Radioactive devices -- some of which have the potential to be used in terrorist attacks -- have gone missing in alarming numbers in Canada over the past five years.

A new database compiled by The Canadian Press shows that the devices, which are used in everything from medical research to measuring oil wells, are becoming a favoured target of thieves.

At least 76 have gone missing in Canada over the past five years -- disappearing from construction sites, specialized tool boxes, and generally growing legs and walking away.

Some of the devices could be used in a "dirty bomb," where conventional explosives are used to detonate nuclear material, spreading the contamination over a wide area, said Alan Bell, a security and international terrorism expert from Globe Risk Security Holdings.

He told CTV Newsnet on Thursday that the problem isn't new, but it has gained new attention as a result of the CP report.

"It's come to the fore over the last couple of days but it has always been there. We've had this problem. It's only a matter of time before terrorists use a dirty bomb process to attack the world," Bell said.

The database compiled by CP tracks the rate at which the devices have gone missing in recent years.

It points to dozens of cases where hazardous materials have gone missing, been stolen or lost in a variety of mishaps.

Of the 76, 35 were stolen, three others were found in a ditch beside a road, in a dump and in a farmer's field.

Dozens were still unaccounted for at last count.

Bell said there is a lack of streamlining among the different federal departments responsible for nuclear materials and a single agency should be set up to track the transportation of nuclear materials.

"But one of the biggest problems is yes, we do keep track of them to the best of our ability, but things fall through the cracks as they always do," Bell said.

The CP report comes in the wake of the release of a federal study that said the detonation of a small dirty bomb near Toronto's CN Tower would send radiation out over a four kilometre area, causing economic devastation and slamming the city's emergency medical services.

Bell said such reports could actually help motivate terrorists to strike the city.

"I was surprised. Why tell the terrorists where to place the device? This is the ramifications of the weather, this is the area that's contaminated or affected. I thought it was irresponsible to do that."

He said terror attacks around the world have become more sophisticated in recent months, and "it's only a matter of time before they gravitate to using nuclear material in their bomb box."

With files from The Canadian Press