xrays are no fun... do a search on kodaks tests with Xray fogging. Significant fogging from just 1 pass, esp with color films. try to ask for a hand search of film (TSA may not care and xray it anyway), buy the film there (maybe very hard), develop it there (I dont trust labs with my stuff) or mail it back with a carrier that is not big on Xraying materials.
The problem is not just an even coat of fog, BUT very nasty banding issues. imagine a light leak. not fun at all
its a tough thing to do nowadays. I was on a cruise last summer and they Xrayed my bag every time we boarded the ship. (I carried a digital only though)