How exactly does radiation "stick" to objects and living things?

Submitted by ibex333 t3_xx6zxo in askscience

How can ionizing radiation stick to things? Radiation is not matter. It is invisible, you cannot "touch" it or hold it. And yet, apparently you CAN wash it off, at least to a certain degree. What gives?

Stranger still, is the fact that objects which have been contaminated, somehow "lose" radiation stuck to them over time! Yes, I read somewhere about half-life of elements and whatnot, but what does a half-life of uranium-238 for example, have to do with the radiation that it gave off which in turn stuck to something? Radiation is not the element itself, it is energy, so how can it "decay" like the element that originated it?

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colcob t1_irdy4yp wrote

I can't really answer your question, but just wanted to clarify your 'radiation is not matter' statement.

3 of the 5 major types of radiation are in fact matter. Alpha, beta and neutron radiation are all particles of matter. Only Gamma and X-Rays are an electromagnetic wave.

As others have said, often it's that the radioactive material itself has 'stuck' to things, although Neutron radiation does have the ability to make make other materials radioactive.

http://hps.org/publicinformation/ate/q12968.html

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mfb- t1_irdt61s wrote

Radiation doesn't stay around for more than a millisecond.

Radioactive material can stick to things and keep producing radiation. You want to avoid getting radioactive material on you or your clothes, and washing it off is effective: The material will still produce radiation but now it doesn't do that on your skin (or worse, in your body if you inhale o eat parts of it). Typically cleaning is much faster than the half life of the substance being handled.

To a really good approximation, radiation doesn't make other things radioactive. Induced radioactivity is an extremely weak effect. It's only relevant if you remove material from a nuclear reactor or parts of particle accelerators where they have been exposed to very high radiation levels.

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Sevulturus t1_irem9hs wrote

This, where I work we used radiation to measure the levels of molten metal in molds. We have devices that are constantly bombarded by radiation, the amount that gets through let's us know how full the molds are.

We had biweekly checks of the system where we made sure that no radioactive material had left the enclosure it was held in. But the scintillators (reading device) never became radioactive.

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ChrisGnam t1_irgbmmq wrote

As others have pointed out, "radiation" is the energy "radiated" away from something. It could be electromagnetic radiation (radiowaves, microwaves, visible light, X-rays, gamma rays, etc.), or it could be particles (alpha or beta particles).

When we talk about washing off radioactive contamination we mean removing the radioactive particles that are emitting the radiation. If you get covered in Uranium dust, you are being exposed to all of the radiation being released by that dust. Washing it off of you removes that source of radiation thus protecting you from further exposure.

As for how there is a half life to the contamination, remember that what we're concerned with is the radioactive material itself. Radioactive material is just material that is unstable at an atomic level. That instability means it will randomly break apart, emitting energy (radiation) in the process. Once a given atom has broken apart though, it can't emit more energy.

With a large collection of radioactive material different atoms will break apart at different times, releasing their energy in a somewhat constant stream. But over time, as more of the individual atoms break apart, there will be fewer unstable atoms left. Eventually, all of the atoms will have broken apart, and so the substance will no longer be radioactive. For many things, like Uranium, this takes a very very long time though.

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