Radioactive

What does it mean to be radioactive? Not the song, the scary, potentially-cancer-causing state of radioactivity...the song isn't very instructive, but the music video sure is weird. Radioactivity is NOT the same as radiation though - most radiation isn't radioactive; radio waves and the heat off of a fire are both radiation, but they wouldn't have radioactivity.

WATCH OUT - But it's not actually that scary...

If a substance is radioactive then it's giving off tiny particles or energy waves that are so miniscule that they can go right through our bodies. This is fine if they just pass right on through, but they're also small enough to hit the nuclei of our cells, where the DNA is stored, and change that DNA. If it changes the DNA to make that cell start replicating uncontrollably, then it becomes a "disease" that you've all heard of: cancer.

 

"Ionizing Radiation" ('z' and 's' are both right) is the specific type of radiation that's radioactive.

Now this is all an odds game! You could be exposed to a lot of ionizing radiation and never get sick or even notice, because all of the particles happened to miss your DNA. The main thing all of this radioactive stuff has in common is being very tiny, which is why microwaves CANNOT give you cancer. Certainly you wouldn't want to be inside one because it would get very hot, but the waves are simply too big to change your DNA.

Only the 'ionizing' area can be cancerous - but don't worry, x-rays are VERY low risk. (source)

Where does all of this radioactive material come from though? All atoms naturally decay, or break apart - bigger ones more quickly than smaller ones, which is why plutonium and uranium, some of the biggest naturally occurring elements in the universe, are so radioactive. Their nuclei are so big that they naturally tear themselves apart, which is why we use them in nuclear power plants (nuclear being similar to nucleus is NOT a coincidence - nuclear reactions are the only time the nucleus of an atom changes, otherwise it's just a normal chemical reaction like burning wood or digesting food). 

Check out this video about some of the most radioactive places in the world, it's seriously so good:

The most radioactive place MIGHT surprise you...

This is a pretty complicated topic, so please ask any questions you have in the comments - there are no bad science questions! Also check out this article from The Onion, it's satire so it's fake news but it's hilarious.