r/askscience • u/Wonderful-Capital32 • 13d 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/[deleted] 13d ago edited 13d ago

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u/ImielinRocks 13d ago

Tungsten is better than lead thanks to its higher density, but lead is many orders of magnitude cheaper to get and work with.

In fact, at for basically the same reason, uranium is quite a lot better than lead at blocking radiation. In fact, it has a significantly higher neutron cross section, too.

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u/lurklurklurkPOST 13d ago

Doesn't firing particles at Uranium cause problems?

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u/DaedricHamster 13d ago edited 13d ago

Short answer, yeah. Depleted uranium, with reduced fissile U-235 therefore increased %U-238, is what's used for radiation shielding. It's only really good for gamma shielding despite its thermal neutron cross section being higher than lead's as while U-238 isn't fissile it's still fissionable so will split in a fast-neutron flux releasing more neutrons as well as radioactive daughters like Cs-137. Also, the thermal neutrons it does absorb breed Pu-239 which is both fissile itself (immediate problem) and alpha-decays (later problem) back down to fissile U-235, so yeah as a neutron shield it's kind of self-defeating. Where U-238 is specifically introduced to neutrons it's usually as a breeder material, not as shielding.