If they really wanted to test something, they would use a much less powerful source hidden in a container that wouldn't normally be scanned.

a "screwed-up" (http://www.imdb.com/title/tt0433116/)

You do realize you are basing your assessment (and its very serious implications) on a movie, right?

my assessment has no implications, unfortunately. Movie reference is used only as a funny humorous illustration. My assessment is based on my knowledge and experience with real government screwedups even here in the US, like county office messing up real estate ownership info. Compare to that, planting the tracer into the container that will most probably be checked is hardly a screwedup.

If would find the implications of this being a test run disturbing. Luckily, we can dismiss it.

Unless, of course, we start considering what else came through that port while so much attention and resources were focused on one very radioactive container.