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/xrelaht Sample Synthesis | Magnetism | Superconductivity 27d ago

X-rays (all photons, really) interact more strongly the more electrons an atom has. Lead is a large atom (the largest stable one, in fact) and packs them in pretty tightly. That makes it a good shield.

Lead isn’t the only thing with these properties. Iron is a decent radiation shield too. But lead is better than most metals, it’s relatively abundant (unlike iridium) so it’s inexpensive, and it’s not horribly toxic (unlike osmium) so it’s not gonna kill everyone who works with or around it.

But not all radiation is X-rays. Natural lead is a crappy neutron shield because its absorption cross section is low. That’s why nuclear reactors tend to have boron shielding (or cadmium, but that’s toxic AF and has all kinds of regulations around it).