I watched the Chernobyl miniseries recently and read up about some of the specifics a bit. A lot of it is still beyond my comprehension, but I ran into the picture below (i hope you can see it):
It says (among other things) that sleeping next to someone increases your absorbed dose of radiation, and also that eating a banana increases your absorbed dose. From what I understand so far, many things (I assume mostly organic things) are a bit radioactive. Is this true and if so, why?
In: Physics
There are different isotopes of elements. Different isotopes have the same number of protons, but a different number of neutrons. This changes their properties slightly, for example, making them radioactive. Many of these isotopes are naturally occuring, so if you have an object of a large enough size, there is a good chance that they are *very* slightly radioactive, yes. But you will never really notice it.
For example, bananas include potassium. They include different potassium isotopes, mostly Potassium-39 and Potassium-41, which are stable and not radioactive, but also a small amount of Potassium-40, which is radioactive.
carbon 14 and and potassium 40 are radio active and just kinda naturaly exist in the world around us (iirc more carbon 14 is made when cosmic rays hit carbon right)
You are made of carbon (mainly carbon 12) from nature, and carbon 12 and 14 are chemically identical, so some of your carbon is carbon 14 (also how carbon dating works). same for bannanas, and they also are a good source of potassium, some of which is potassium 40.
dont worry about it at all. these levels are natural and so far bellow the danger level its irrelevant. take a bit to look at https://xkcd.com/radiation/ and https://what-if.xkcd.com/158/
In this context, radioactivity refers basically to the debris being released when an atom breaks apart. You are correct: basically, an atom of every kind of chemical element *will* break apart eventually, and when it does, it will release radiation. The closer you are to literally anything — including another person — the more times you’ll be hit by that radiation. In the case of bananas, they will contain very trace amounts of atoms more prone to breaking down, like potassium-40.
**However** the amount of radiation released by these background naturally occurring objects is pretty much always miniscule compared to what could be released in something like the Chernobyl accident. This is where the “half-life” concept that gets referenced frequently in Chernobyl comes in. We can roughly gauge how dangerous something could be by how long its half-life is, meaning, how long it will take for this natural breakdown process – called decay — to destroy half of a sample of something. The half-life of the potassium-40 that’s giving you that radiation dose from a banana is about a billion years. At that point, the amount of radiation being emitted from a banana is so miniscule that it’s never going to hurt you in the course of a human lifetime, even if you could somehow carry it around in your pocket for your whole life.
In contrast some chemicals produced and released in the course of something like the Chernobyl accident are very radioactive and have short half-lives. For instance, iodine-131 has a half-life of only a week, which means that if you had a banana-sized sample of *that* in your pocket, it would be releasing quite a lot of radiation.
Because space is highly radioactive.
The sun is an absolutely massive nuclear fusion reactor spewing out insane levels of radiation into space.
The Earth’s magnetosphere and atmosphere keeps us protected against most of it, but not completely.
Some rays hit the ground. Some hit air molecules and turn them into other (radioactive) particles.
Radioactivity is only dangerous at certain levels and in certain forms.
Some of the most dangerous forms did get released in Chernobyl and are not present in significant quantities in nature. But those forms also disappear quite quickly.
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