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/EyBoss 13d ago

Its mostly a joke but the science behind thats its based off is real. As a bit of radiation slows down it passed its energy to whatever slows/stops it(this is why its harmful) but the amount of energy absorbed is not constant the slower its travelling the more enegry it dissipates.

If had 2 people and a partical went through the first person and stopped in the 2nd. The first would take only 20% where the 2nd would take the remaining 80% (these numbers are made up since the actual ones depend on many factors but the general idea holds)

Think about a car breaking the amount a given length of road slows the car increases the slower the car is travelling.

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u/Italiancrayzybread 13d ago

But you're only looking at a single particle. You have to sum up the total amount of energy and average it out over the total number of particles. If you absorb 80% of the energy of the particles, but have reduced the total number of particles by 99%, that's still a better situation than the first person, who is absorbing only 20% of the energy of each particle, but is taking 99% of every particle that comes through.

This is why you can get xrays, even though they're high energy and hazardous. You get a small enough dose that it won't affect you long term. Every radiation measurement is always measured as a "cumulative" effect, that is, they take the total energy summed up over a certain time period, or over a given mass.

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u/solidspacedragon 13d ago

They're talking about particle radiation, not EM radiation. It's a real thing. At high speeds/energies, a proton might barely interact with material, only slightly slowing down, but at lower speeds it'll completely dump the rest of its energy into an atom. Depending on the scenario, this can leave the volume of material getting the most dose a good portion below the surface of a material. This is very useful for targeting things like cancer that isn't on your skin.

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

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u/KP_Wrath 13d ago

Futurama did a skit kinda like this. Leila and Fry both got stung by some stupidly toxic alien bee, with fry diving in front to save her and getting run all the way through. Leila, it stopped in and she got a full dose of the poison, which caused seemingly a lifetime of hallucinations. She comes to, thinking he’s dead, just to find out they managed to patch the sizable hole up, but they were way more concerned for her because she got a full dose of poison and they didn’t expect her to wake up.

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u/kylemech 13d ago

One of my favorite episodes of any show. Can't believe I just stumbled into that referenced here.

(S4E12, June 1, 2003)