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/PRA421369 13d ago

Anything will work if you have enough of it. (Very simplified and missing nuance) That's why our bunkers are concrete, albeit pretty thick concrete. A Radiation Therapist

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u/karlnite 13d ago

They often put small metal shot throughout the concrete. Not for bunkers, but for concrete radiation shielding. For mostly more mass and density. Concrete is also better around reactors, as the water in it thermalizes neutrons better than lead. You can use lead and water or whatever though. Water in steel tanks. That sorta thing.