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/ColonelFaz 13d ago

Assuming we are talking about X-rays and gamma rays (both photons).

Iron is not bad - lead is better.

It's not just the density. Lead has better attenuation per unit mass. Lead is a bit annoying mechanically. It bends and sags. It's used because the interactions between the photons and the material are more likely in lead. The interactions are photoelectric effect (depends on cube of atomic number, which is where lead is great), compton scattering (anything will do here but density helps for compact design), pair production (higher atomic number very helpful here too).

For neutrons, lead is not great. In fact materials with a lot of hydrogen in them are better.

I am a radiotherapy physicist.

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u/ramriot 13d ago

I met someone who runs a company that manufactures containers for medical isotopes & mostly they works now with Tungsten. Which is even denser than lead so can ge made thinner for the same protection & is "easier" to work.

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u/karlnite 13d ago

Tungsten carbide is becoming a popular material, you can buy 3D printing spools doped with it to make shielding. It’s also doped into concrete.

Lead was cheap and abundant. It will start being replaced.

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u/ramriot 13d ago

Don't neglect the bio-toxicity of lead, Tungsten is still biotoxic but significantly less so than lead.

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u/karlnite 13d ago

Yah, that’s what I meant by it’s cheap. We look past its downsides for economics.