Dirty backpack/suitcase bombs will be more dangerous to Israel than a warhead delivered by a missile.
http://www.pbs.org/wgbh/nova/dirtybomb/chrono.html
The history of the dirty bomb has yet to be written, because fortunately no one to date has ever deployed a conventional explosive laced with radioactive material.
Can we go through the logistics in creating, transporting and successfully detonating a dirty bomb? And, what will the result be of a detonated dirty bomb?
Or, even the fantasy that an Iranian will cross into Israel without being detected that he is soaked with radioactivity (which would have killed him pretty fucking quickly).
Terrorists execute crude & easy (but effective) methods of killing innocents. They use explosives, guns and have used airplanes. The airplane attacks were mostly due to social engineering as far as I am concerned. Americans need to wise up; but not to the point where they conduct witch hunts and compromise their freedom to live and enjoy life.
But, we have yet to see sophisticated, coordinated and successful attacks that involved radioactive materials.
Now, by all means, take the measure to ensure they don't detonate a dirty bomb - LIKE A FUCKING GEIGER READER. If some asshole shows up with something the SCREAMS red flags (dirty nukes are just that - dirty; akward looking, etc) and he is LEAKING radiation (that has yet to somehow NOT kill him yet), you shoot him.
If he is capable of hiding the radioactivity - then you have another problem on your hands; you are facing Superman or something capable of lugging all those layers of lead and protection to keep the radioctivity from spilling out and he wants you dead. Do you think he will detonate himself,... or just outright kill you with his super strength?
How many 13lb lead bricks will you need to mask a dirty bomb?
http://www.drct.com/lead_bricks.html
And, if the moron at the TSA security check doesn't realize that 10 of these suckers in a teddy bear don't make any sense, then you have another entirely different problem on your hands; Terrorist Superman wasn't labeled as a problem, as he carried a 130 pound lead teddy bear that still gets picked up by a geiger reader - time to get a new TSA security agent.