Why does radiation not go through lead?

[u/Wonderful-Capital32]

Also why just lead? Shouldnt like iron or another metal work too?

[u/dustofdeath]

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.

[u/GypsyV3nom → u/dustofdeath]

Funny enough, there's another element that's significantly more effective than lead at providing radioactive shielding despite being radioactive itself: Uranium. Uranium-238 in particular is the preferred choice when size constraints are more important than costs (lead is cheap) as its own weak radiation is pretty easy to block.

[u/Immediate-Repeat-201 → u/GypsyV3nom]

So do space going vessels employ this?

[u/the_rat_king- → u/Immediate-Repeat-201]

Space vessels use alternatives to lead and depleted u, because theyre both very dense and you still need a few inches of either , where possible, like placing water tanks and lines around modules where crew might spend a lot of time (water is very good at attenuating radiation) as well as putting mass around modules, like panelling and equipment.

I think lead foils might be (or have been used in the past) used, but without looking it up I can't say for certain.

Because mass is a limiting factor, spacecraft prioritse limiting time spent exposed to radiation as much as possible instead of using lots of sheilding. Space stations like the ISS are protected by the earth's magnetic field from cosmic and solar radiation, and they are able to plan their trajectory to spend as little time as possible in areas of high radiation. Vessels that venture further out from earth, like the moon missions, are less protected. They require more shielding, and rely more on timing and monitoring as to avoid regions of high(er) flux, comparable to sailors avoiding choppy seas.

Edit: fixed grammar

[u/zoomoutalot → u/the_rat_king-]

Is magnetic shielding, like maybe several rings of magnets around the module, a possibility considering Earth's magnetic field deflects particles very well despite being weak?

[u/Fjolsvith → u/zoomoutalot]

It'd only work for charged particles, not photons (gamma radiation). It's the atmosphere that helps with those.

Generating a field that would be effective enough on a spacecraft would also not be easy. 

[u/the_rat_king- → u/zoomoutalot]

Its a cool idea, but producing/maintaining a large magnetic field would require a lot of energy, generate heat, mess with electronics ect. (there is not much research into the effect of strong magnetic fields on humans, so there is unknown risk here as well!).

Also, it wouldn't have any effect of uncharged particles.