That is not totally true. Semiconductors do care. When
x-rays go through
a simiconductor, it creates electron/hole pairs. With no bias on these, they
usually just recombine. With bias, these become current flow. To add to
insult, this current can be amplified by parasitic transistors as exist in
devices. This can lead to a high current run away.
Snap, the magic smoke leaks out and that is the end.
Now, the question is, does an airport x-ray machine create enough of this
kind of current to cause damage to a biased device?
Hmmm...Do you know what percentage recombine? This could explain reports
of 50k rad on a device turned off and 11k rad on a device turned on.
Airport machines are puny. 120-160kv and a few ma. I think you would need
a TON of x-rays to actually damage a device. CCD cameras show bright dot
flashes where x-rays hit the active area, but its nothing that "hurts" them
quickly. It looks like snow, or the star travel type screen savers.
The only electronic device ever to fail from x-rays in my experience has
been those basic stamps. AVRs have held up to limited exposure to a linear
accelerator and the basic stamp died after hardly anything.