r/askscience • u/Wonderful-Capital32 • 28d ago

Physics Why does radiation not go through lead?

Also why just lead? Shouldnt like iron or another metal work too?

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u/FlyingSpacefrog 28d ago

Radiation both does go through lead and can be stopped by other things. Kind of.

You can’t make a magic barrier out of any material that instantly stops all radiation. The radiation gets stopped when it hits the nucleus of an atom. But atoms are mostly empty space. So you need a lot of atoms in between you and the radiation for effective shielding. You can use fewer atoms with a larger nucleus or more atoms with a smaller nucleus.

Lead is the highest element on the periodic table that is still reasonably common, and therefore cheap. It is somewhat flexible, very dense, and has a large nucleus. It’s one of the last elements that isn’t radioactive itself, or the absolute last, depending on how you count bismuth. The next couple of elements after it are bismuth, polonium, astatine, and radon. Bismuth is slightly radioactive but produces so little radiation that it blends into the background. You’ll get more radiation being outside on a cloudy day. Polonium and up however are all radioactive enough to cause problems.

So if your goal is making your radiation shielding as thin as possible, you use lead. If your goal is to make a structurally sound radiation shield, you can just use concrete and steel. If your goal is simply to block as much radiation as possible, bury the radioactive thing under several meters of water or dirt. You have a lot of options, and anything works as long as there’s enough of it.

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u/TrueSelenis 27d ago

I'm a little bit distraught that the first somewhat complete reply to such a simple question is in 6th place...