According to breaking reports the FBI has been monitoring mosques and private addresses without warrants for the last few years.
Details here:
http://www.dallasnews.com/...
http://www.azdailysun.com/...
http://news.bbc.co.uk/...
Monitoring for nuclear materials isn't an inherently bad thing - although as someone with some science background I'm not convinced that driving around in a truck is going to reveal much in the way of stray radiation, no matter what it's equipped with, if potential terrorists are smart enough to use proper shielding.
But the issue here is that the monitoring has been taking place without warrants, without judicial oversight, and apparently without prior intelligence.
In other words this isn't evidential monitoring - it's simple fishing. And if it's being done to Muslims for these random reasons, can anyone say for sure that analogous physical monitoring isn't also being done to Quakers, vegans, people who don't celebrate Christmas, and other potential threats to national security? (You know how it is - just because they don't have neutron sources in their homes doesn't mean they're not terrrrists.)
I think a lot of people are going to be hoping that as the scope of spygate continues to widen, this is going to be one of the issues that pushes the illegality of these actions closer and closer towards a realistic possibility of impeachment.