http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20070704/devices_disappear_070704/20070704?hub=Canada

Excerpt:

"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....

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..."