How is radioactivity spread/contaminating anything that it comes into contact with?

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Just finished watching Chernobyl, and I’m curious what the effect/process is by which radioactivity is spread from one human/surface to another? What particle is responsible?

Thanks

In: Physics

Dust made from debris that was within Chernobyl can be highly radioactive and easily moved and transferred from place to place.

Often people misuse the words “radiation” and “radioactive contamination”.

*Radiation* refers to energetic subatomic particles or light that is emitted from an atom. This includes alpha particles and beta particles (both subatomic sized) as well as gamma rays. *Radiation* is emitted in a straight line and causes chemical reactions in objects that it hits, but it does not make other things radioactive.

*Radioactive contamination* refers to small pieces of radioactive material. Each piece of contamination (which can be large pieces, dust sized, or even smaller) contains millions of atoms that individually emit radiation. Like regular dust or dirt, contamination can be spread around by surface contact or in an airborne fashion.

At Chernobyl, the reactor was severely damaged and caught fire. The fire spread large amounts of *contamination* (individual pieces of highly radioactive material) into the local area and the atmosphere.

Think of all of radiation as a form of light. The radioactive source material is the light source, and the radioactive particles (alpha, beta, gamma, and neutrons) can be thought of as the light. If you were able to look at Chernobyl and see this light after the explosion, it would look like a giant light source was lighting everything up around it, with some walls and objects even appearing translucent. The air would scatter some of this light, and essentially, if you see the light, you’re being irradiated. If you look directly at the light source (the reactor core), then you’re being severely irradiated. Even just opening up a door around the reactor room would cause very high doses of radiation, just like if you were standing in a dark room and opening up the door to a well lit room. It lights up you and your dark room significantly.

All of that light interacts with the materials it bounces off of and can sometimes cause that material to become radioactive as well. This is common with things like the graphite moderator used in the reactor core, as well as with some of the pipe and valve material used in the reactor construction. Even before the explosion, much of this material was slowly becoming new sources of radiation. So, if you saw pieces of the core laying on the ground around you after the Chernobyl explosion, some of them would be glowing. The pieces of graphite on the ground would glow exceptionally bright, and would have been a very large source of radiation for the firefighters standing around them.

When the fires were burning, they burned radioactive material, which released radioactive ash into the sky. When the steam explosion happened after the fire department sprayed water all night, that steam carried small radioactive dust from the reactor with it. So what you would see if radiation looked like light, would be glowing ash and steam floating in the air, depositing glowing pieces of radioactive material all over town and the surrounding area.

The glowing ash, steam, and chunks of glowing reactor material on the ground around the building are called contamination. This radioactive material that was once held safely inside the reactor is now spreading around and contaminating areas outside of the reactor. Wherever someone comes into contact with this contamination, they would receive large doses of radiation. Basically, if they can see the glowing ash or chunks of graphite, that light reaching them is radiation, so they are being irradiated.

It’s important to note that in this analogy, you would see a small glow everywhere you looked, even before the explosion, or even in remote areas away from the reactor. This is called background radiation and it comes from many natural sources, such as the sun, cosmic rays, and naturally occurring radioactive elements in the ground and rocks. It’s very minimal, and isn’t known to cause long term negative health effects, but it’s there. Also, if you live in areas with a lot of granite or exposed bedrock or at higher elevations (especially when flying), you would see a stronger background radiation glow.

We always explained it like this “it’s like stepping in dog shit. The smell is radiation, the shit is contamination. You can eventually clean off or sequester the shit, but you can’t do anything about what you already smelled.”