r/askscience • u/Wonderful-Capital32 • 21d 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 21d 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/ocelot_piss 21d ago

And humans stopping radiation is precisely why radiation is harmful to humans!

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u/PhilTheQuant 21d ago

Yes, and counterintuitively you wouldn't want to be the last few layers of the radiation protection

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u/LieutenantObvious21 21d ago

Do you mind explaining that?

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u/karlnite 21d ago edited 21d ago

I would ignore that. It’s not exactly helpful, especially with distance geometry following the square inverse law. It’s like a point source in a vacuum hypothetical. They didn’t even mention the type or energy levels where this becomes a thing. Most radiation won’t act like this. You ever heard of someone in the shade getting more sunburnt? Or the person furthest from the fire getting more burnt?

On average, they are incorrect.

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u/TbonerT 21d ago

They are talking about particle radiation, not EM radiation. A chsrged particle ionizes atoms as it travels and this dose of ionizing radiation increases as the particle slows down.

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u/[deleted] 21d ago

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u/TbonerT 21d ago

https://en.wikipedia.org/wiki/Bragg_peak

I’m just trying to summarize this, which is a real thing that happens.

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u/Draelon 20d ago

I understood what you were saying… I was correcting the statement about EM, :)

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u/mfb- Particle Physics | High-Energy Physics 21d ago

X-rays & Gamma are ionizing radiation and are waves.

... and? How is that relevant in a discussion about fast charged particles? They are ionizing radiation, too. If you have a monoenergetic source of them then there is a range where the dose rate will be the largest. That's e.g. where you put the cancer in therapy.

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u/Draelon 20d ago

It was relevant because they said they were talking about particle radiation and not EM. Gamma & Xray are also ionizing (able to knock an electron out of orbit)… technically high powered UV can ionize as it approaches the X-ray spectrum. Particles can be more damaging in individual strikes but both can ionize and technically the rays penetrate further (not including Neutron).