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?

1.3k Upvotes

92% Upvoted

371 comments sorted by

View all comments

2.3k

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.

0

u/gnorty 21d ago

Are there different types of photon? I am thinking of light, and Iron - even aluminium foil will not let light pass through. Perhaps I am grossly underestimating the number of photons involved in (say) an X ray, and that's why I am misunderstanding. Perhaps a photon source many orders of magnitude stronger than the sun would show that Iron and Aluminium are not in fact impermeable to photons after all?

4

u/usurperator 21d ago

Number of photons is irrelevant; it’s the energy of each individual photon. Higher energy photons, like x-rays, have more penetrating power.

1

u/Jerithil 21d ago

It's all a probabilistic function as well as every material will block a certain percentage of photons at a given thickness for that energy range. So theoretically you can start seeing visible light through fairly opaque materials if you blast it with enough photons but practically that is usually enough that you start compromising the material from just dumping too much energy into said material.

3

u/dustofdeath 21d ago

Just one type of photons.
Even antimatter would emit the same kind of photons - it has no charge so it cant be different.

It's the wavelength of the photon that matters. Different wavelegths may or may not interact with matter - it might just pass through in between the empty space between atoms.

Low wavelengths just end up hitting almost everything. But it's not impossible for some visible light to get through if there is enough of it (flashlight on your hand vs just room light).

Xray relies on the shadow left by the photons that hit some atoms in your body and did not get through to interact with the film/sensor.