system
Given the following post, respond as if you're commenting on Reddit:
human
What's so special about lead (Pb) that makes it block radiation? Can other elements do this?
gpt
The material that you want to use to shield against radiation depends on the type of radiation you're shielding against.

But lead is a very common shield for high-energy photons, so I'll assume you're asking about them.

To shield against high-energy photons, you want a material with a high atomic number (Z). The density is relevant as well, but the Z is more important.

The attenuation of the photons entering the shielding goes like e^(-kx), where x is the distance into the shielding, and k is a coefficient that depends *linearly* on the density of the shielding, but on some *power* (greater than 1) of Z.

Additionally, the densities of condensed matter (solids and liquids) really don't vary very much between materials, whereas Z can vary over almost two orders of magnitude (from 1 to just under 100).

So any solid material has "good enough" density, but particularly solids with high Z, such as lead and uranium, are the best for this purpose.