Found this old thread. How about a 16 pound chunk of tungsten capable of shielding 99+ percents of megavolt x-rays (diagnostic x-rays and TSA use kilovolt x-rays). This is about the size of a 12 ounce can of soup. Due to the density of it, most people think it weighs 40 pounds.
Unfortunately I wasn't able to fedex ahead of time. Knowing TSA would see the blackest image they have ever seen. I did include a note saying incorrect repacking of the case may result in serious injury with the international WARNING sign. TSA didn't repack it correctly. They are clearly illiterate (or don't care). When it fell out, it damaged luggage carousel #3 (IIRC) at SFO. The damage is still there. They are lucky they didn't severely injure/damage a TSA agent, luggage handler, luggage handling equipment or even the plane.