darling, if you want an excuse to infodump, I am here for you! I would love to learn all about radiation!
Thank you! Oh, gosh, where to start?
So, technically, 'radiation' can refer to all kinds of electromagnetic radiation from visible light to radio waves to microwaves to UV to what everyone actually MEANS when they say radiation: ioninzing radiation. That's the stuff that has enough energy to ionize other atoms - and therefore can cause damage to things like humans. It's what you think of when you hear about radioactivity, nuclear power plants, or the Chernobyl accident.
This is going under a cut now because it's getting VERY long:
Ionizing radiation, though, is not one singular thing - it breaks down into a bunch of other types. Some of them are particles with mass (alpha particles which are essentially helium nuclei minus the electrons, beta particles with are JUST electrons but they go really fast, neutrons which are also like a very high-energy version of the ones inside of atoms) and some of them are essentially weird light (gamma rays, x-rays).
But mostly people talk about alpha, beta, and gamma radiation when it comes to radioactivity. I'm honestly not sure why. I think they might be more common in nature on earth than some of the other stuff?
Other key point - radiation is all around us all the time. So are various radioactive substances - stuff that emits radiation. You've heard of carbon dating? That works because some tiny percentage of all the carbon on earth is carbon-14, which is radioactive. That means you, a being made of carbon, are slightly radioactive.
Also if you've heard the whole 'bananas are radioactive' thing - yes it's true, no it won't hurt you, and that radioactivity comes from the potassium-40 isotope, which makes up a small fraction of all the potassium on earth. You, a human being, also contain potassium. This also contributes to you being slightly radioactive.
Outer space is radioactive for various reasons, including that stars are powered by nuclear fission reactions. And they're just spewing radiation across the cosmos. Some of that winds up on earth and we call it cosmic radiation.
The amount of radiation we're all exposed to from normal, everyday stuff is pretty harmless, and it's called background radiation. In addition to carbon, potassium, and outer space, it comes from lots of other things including rocks and soil (uranium, for instance, is naturally occurring and way more widespread than you'd think, though often within other minerals - it's not always uranium ore) and various human activities (remember how we exploded some nuclear bombs like eighty years ago? some of that stuff's still floating around). Medical scans like x-rays are also a fairly significant contributor to the average annual dose of radiation. There are way more human activities that create or concentrate radioactive substances, but I won't get into all of them because this is long enough already.
When radiation gets dangerous is at levels significantly above background. Remember what I said about it ionizing other atoms? Well, sometimes that damages things like cells and DNA. Your body has mechanisms to try and repair that damage, but they don't always work perfectly and if those systems get overwhelmed by really high levels of damage, you've got problems.
Radiation can hurt you in two main ways: acute and long-term problems. The most obvious acute example is radiation sickness - radiation burns are also a thing. That happens when you get a BIG dose in a short period of time. If you get a smaller dose, especially repeated small doses over time, that's where increased cancer risk becomes a problem.
Oh, I forgot to mention - the different between radiation exposure and contamination is key here. Exposure is like when you get an x-ray - the radiation passes through you and either leaves ro gets absorbed. You are not carrying x-rays around with you afterwards. Contamination is like if you touched a piece of uranium ore and got dust on your hands - you are carrying the source of radioactivity around on your person. It is continually producing radiation which you are being exposed to, and you can spread the dust or whatever to other people and objects. You can get rid of it by washing your hands - most of the time.
Contamination on your skin isn't that bad because you can just wash it off. However, if your food or water has radioactive stuff in it, or if the dust is in the air and you breathe it... that's bad. Potentially very bad. Your body tends to absorb that stuff and hang onto it - how long depends on what nuclide the radioactive material is made of. A nuclide is like an isotope, but for radioactive stuff. You know how isotopes are slightly different versions of elements, with different numbers of neutrons than usual? Nuclides are slightly different versions of elements which have different amounts of nuclear stability - some are stable and some are radioactive, meaning that their nucleus is unstable and needs to emit radiation in order to stabilize itself. That's why radiation happens. Radionuclides are the unstable ones.
Anyways, some nuclides get absorbed into the body really easily and are hard to get out once they're in there. Some are more dangerous than others. Your body is going to slowly excrete them over time, and they'll also be decaying, but they can still be in there long enough to cause plenty of problems.
One of the radionuclides that was really concerning after Chernobyl was Iodine--131. This is because your thyroid loves to absorb iodine - any iodine. It does not know or care the difference between the normal versus radioactive stuff. And if it absorbs the radioactive iodine, then it's gonna hang out there for a while and damage your thyroid cells, which can cause cancer. And after Chernobyl, that's exactly what it did. People who were nearby did experience higher than usual rates of thyroid cancer in the years afterwards.
So. Internal contamination can be scary. Radioiodine is actually one of a few radionuclides where an effective medical treatment exists. However, that comes with a LOT of caveats. The drug is called potassium iodide, and it works by flooding the thyroid with safe, non-radioactive iodine before or shortly after exposure to radioiodine. The goal is to make your thyroid absorb that instead and go 'no thanks, I'm full' when the radioactive stuff comes along. Then your body will excrete it faster and it won't cause as much damage.
But potassium iodide (aka KI, because potassium is K on the periodic table) only works if it's taken within a few hours before or after exposure, and then it only works for 24 hours. It can have serious side effects if taken for too long, and people can be allergic to it - especially people will shellfish allergies, for some reason. And it won't protect you from any other type of radiation - only radioiodine.
With most other internal radioactive contamination, you just gotta treat symptoms.
There are ten million other things I could rant about but I'm running out of stream so I'm gonna stop for now. Thanks for asking!
