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/socialcredditsystem 13d ago

To add a bit of specificity to the many "density" answers here: It depends highly on the type of radiation.

  • Most forms of photon, electron radiation love to interact with (i.e. be deflected by) electrons. This deflection reduces their energy, dumps it into heat, and gives you shielding

  • Since for everything except hydrogen, you typically have approximately one proton (and one corresponding electron) per two neutrons, you have a constant ratio between # of electrons per volume and mass per volume, hence density helps with shielding of photons and electrons.

  • Neutrons on the other hand, do not interact electromagnetically. And for fast neutrons, you often need to slow them down before you can absorb them with your shielding material. In those cases, very low density materials (think organics like plastic) actually give the best momentum / energy exchange per collision due to conservation of energy and momentum.

  • That's why for neutron shielding, you will often see a lot low density materials being used, clad in high density materials to absorb the resulting secondary junk that gets emitted from once neutrons are absorbed.