What makes an object contaminated with radiation?

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So I’m talking about something like Marie Curie’s notebook for example. It’s still highly radioactive, but why? What causes a non-radioactive object that’s been left in radiation to become radioactive?

Also does the same reason apply to all matter? If so, how are some items like surgical scalpels and even some food sterilized by ionizing radiation?

In: Physics

It depends on the type of radiation. Microwave, X-ray, Gamma Ray. I mean even light is a form of radiation. So are radiowaves. Try reading up on the electromagnetic spectrum. Radioactive elements emit more powerful forms of radiation. Also, it depends on the type of material it’s emited onto. Which is why you wear lead padding when getting an X-ray instead of notebook padding.

It’s been awhile since I’ve studied radioactivity. But it’s a broad and complex field of study. I hope this is ELI5.

Generally it’s contaminated with traces of the radioactive material itself. In other words in the case of Marie Curies diary, it’s probably got traces of radium on, and in it. The paper itself isn’t radioactive, but it contains contaminants that are.

Sterilizing things with radiation, exposes them to radiation, but they don’t come in direct contact with the material that is the source of the radiation, and so they don’t become contaminated

Every time you handle an object little bits and pieces of it break off and get left behind on you and whatever surface you were working with. You don’t normally notice this because the amount of material that breaks off is very, very small.

Some materials, such as the paper that her notebook is made out of, are porous. This means that if you look at them under a microscope they’ll look somewhat similar to swiss cheese in that they’re filled with holes. If you’re working with a material near a notebook, some of the bits and pieces that break off of the material will float over to the notebook and get trapped inside of its porous structure.

If you spend a lifetime working with highly radioactive material near a notebook then eventually enough of that radioactive material will break off and get trapped in the notebook that the amount of radiation that it is emitting becomes significant. But its not the notebook itself that’s emitting it, its the already radioactive material that you were working with that got stuck in the notebook that is emitting the radiation.

This is also why she had to be buried in a lead coffin. While she was working with that material some of it was getting on her hands. It would then rub off onto her food and she would eat it. Most of the things that she was working with were metals, and your body will store most of the metal that you eat in your bones. Once its in your bones, its there forever. After spending a lifetime of working with radioactive material, you ingest enough that there is so much of it being stored in your bones that they become dangerous to be around.

Ionizing radiation doesn’t cause a change in the nucleus of an atom, and so exposure to the radiation itself won’t cause something to become radioactive. To become radioactive, you need to have some of the source get rubbed off on you.

There is also something called “neutron activation” that can occur when a free neutron collides with an existing, non-radioactive atom. In certain cases this neutron sticks to the atom’s nucleus and turns it into a radioactive isotope of that atom.

This is a way that atoms can become radioactive merely by being exposed to a source that is emitting neutrons. Neutron emission is not ionizing radiation, but does occur in some otherwise radioactive materials. This only really happens in the context of things like nuclear reactors, however, and isn’t responsible for the radioactivity of Marie Curie’s notebook.

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