Quote:


I thought it was because fusion changed one element to another ... Hydrogen to Helium, for example



It's called "fusion" because nuclei *fuse* together to form a different element. In fission a nucleus splits into either more than one nucleus, or just a different element plus debris.

All of those reactions result in debris along with the new nucleus/nuclei. Some of that debris is referred to as "radioactivity".
_________________________
"If they can't picture me with a knife, forcing them to strip in an alley, I don't want any part of it. It's humiliating." - windsock