Of Car Bombs and Spectrometers

There's something that's been eating away at me regarding the security situation in Iraq. Too many good people are being killed or maimed by car bombs in Iraq. I'm definitely no physicist, but doesn't it seem feasible to position spectrometer-based sensors on major intersections in the Sunni triangle to detect these fascists?



Heck, maybe this already exists. But, if so, it would be good to hear about some successful interceptions (or, as I like to call them, "premature detonations") of car bombers.



Use the Comments feature, below, if you have an idea why this is so difficult to achieve.