Mad scientists, microwaves, Al-Queda, Hitler, trolls, your mom...
There are plenty of great ways Radioactivity(tm) is the Choice for You!
You need radioactivity, for many things such as x-rays.
We can use radioactivity to improve our lives, such as through medical diagnoses and treatments and by generating electricity.
a definition
That's a very good question. Congratulations.
Geiger counter measures radioactivity.
Among other things, it keeps the core hot (and molten).
The exact age of the rock.
Radioactivity affect the water molecules. Radioactivity makes it harmful
Only if things go badly wrong and radioactivity leaks from the reactor
What other sort of radioactivity is there?
For example natural and artificial radioactivity.
Radioactivity can be induced in ordinary matter by artificial transmutation.