I am wondering if there are any materials that are allowed by the TSA regulations concerning checked-in luggage that might react to X-rays. This question would fit both Travel and Chemistry. However, Travel would likely know what is allowed by the TSA, but not how these materials react to X-rays, while Chemistry would likely know what materials react to X-rays, but not necessarily if those materials are allowed in checked-in luggage.

I'm not sure on which one I should ask this. It's purely for curiosity reasons, BTW. I have no intentions whatsoever to abuse the information from the answers. At most, I might choose to pack a different item to avoid any unpleasantness.