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I got one of those things for flying:
http://up.picr.de/30738397ga.jpg
I've had portra 400/800 with me on several flights through handluggage and a few x-ray machines. It's rather heavy so i guess there's metal under the plastic surface. It also just appears as a solid block on the x-ray machines but none of the security staff asked me to open and check inside.
No issues whatsoever.
To cut a long story short:
X-ray damage is cumulative and real. The machines vary hugely in the damage they’ll do. Whether or not you notice it, and whether or not it bothers you only you can answer. If you don’t want x-ray damage you need to have it hand checked.