How can be something contaminated by radiation?

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From my understanding, radiation is just gamma rays which are electromagnetic waves with really high frequency (and energy). While I do understand how they can be harmful when exposed to them (killing off cells etc.), I can’t wrap my head around how does something gets contaminated by radiation and continues to be radioactive sometimes for hundreds of years even when the source of the gamma rays is long gone.

In: Physics

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The gamma rays can be strong enough to knock neutrons out of other atoms which makes them unstable. Those unstable atoms might not decay immediately, but slowly over hundreds or thousands of years. It how something like the Chernobyl disaster produced so much radioactive dust, which then settled on the ground everywhere. It was all produced in the intense environment of the reactor / fire. But the radioactive dust (with damaged unstable atoms) might remain radioactive over a much longer period.

Well to start with your classic forms of radiation are alpha radiation (basically, helium nuclei), beta radiation (basically, ~~neutrons~~ edit: electrons/positrons) and gamma rays.

But more importantly, “contaminated by radiation” generally means “contaminated with radioactive particles” rather than “zapped with gamma rays”. Eg, it’s got plutonium dust all over it, or something similar. If you have been contaminated with a substance like this, it will decay over time and irradiate you.

The other form of “contaminated by radiation) means that you’ve gotten a dose of it radiation that transformed materials from nonradioactive elements and isotopes into radioactive ones.

It usually means that it is contaminated by radioactive isotops. Because of the presence of those materials in their systems they become radioctive themselves (although usually not much so as to pose a threat to others than their own bodies), but if consumed by predators they pass the radioactive materials to those, increasing the concentration in the predator’s body. The longer the contaminated food source is used, and the higher up the consumer is in the food chain, the higher the concentration of radioactive materials becomes in the body, leading to radiation poisoning. Note that this culmination of concentration is possible only because living organisms cannot clear out their systems of heavy metals, which radioactive materials are all are.

For example, after the accident in Fukushima radioactive dust has spilled in the water. There it has been absorbed by plants and eaten by fish. These plants and animals are then considered contaminated by radiation, and thus not fit for consumption, especially by humans.

In general, this means that it’s been coated and contaminated with radioactive dust, liquid, or gas. Unless cleaned (which may not be possible), the object will then be radioactive because of the radioactive materials stuck to it.

Nuclear explosions, meltdowns, spills of radioactive waste or material, leaks at nuclear reactors, etc all cause varying levels of this kind of contamination.

An additional issue occurs if a human or animal ingests radioactive materials. Then the radiation is coming from inside your body, and the much more damaging alpha and beta rays (which have little effect from outside) can cause radiation damage.

In general, being exposed to radiation such as gamma rays by itself doesn’t make objects radioactive. However, neutron radiation (mostly produced only by nuclear reactors or bombs) and under certain circumstances powerful gamma radiation can do this.