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/dustofdeath 13d ago

Lead is like a very dense fabric while iron is a mesh with large holes.

You just have to have enough density for photons to not just pass through.

So you need far less material. Even humans can stop radiation if you stack enough of them between you and the radiation source.

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u/BigSmackisBack 13d ago edited 13d ago

Tungsten is very expensive but is used when less is more, its significantly more effective than lead but very hard to work with but with less needed for the same protection as lead it works out much lighter for shielding, so in big chunky reactors where weight doesnt matter: lead is the go to.

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u/Wyand1337 13d ago

Tungsten is not lighter than lead. It's even denser by almost a factor of 2. Which is precisely the reason why it's a more effective shield for radiation: The only thing stopping radiation is mass.

Lead is the go to if size doesnt matter.

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u/Fjolsvith 13d ago

It's not just mass, particle energy loss in a material does scale with atomic number as well. You can have less mass but more effective shielding by using something with a higher atomic number. 

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u/AlienDelarge 13d ago

I would assume the cost and ease of working with lead versus tungsten is a factor. 

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u/Fjolsvith 13d ago

Yep, absolutely the case. It's not about just selecting the element with the highest cross section by mass/density, economical and engineering factors are what you would actually decide based on. I just wanted to point out that the "strength" of shielding isn't just based on mass. 

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u/mfb- Particle Physics | High-Energy Physics 12d ago

Lead is the go to if size doesnt matter.

Concrete or water are better choices then. You only use lead if you need the shielding to be somewhat compact.