radioactivity vs emission

radioactivity and emission both are nouns.

Word	Noun	Adjective	Verb	Adverb
radioactivity	Yes	No	No	No
emission	Yes	No	No	No

As nouns, emission is a hypernym of radioactivity; that is, emission is a word with a broader meaning than radioactivity:

radioactivity: the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
emission: the release of electrons from parent atoms

radioactivity (noun)	emission (noun)
the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay	the act of emitting; causing to flow forth
	the occurrence of a flow of water (as from a pipe)
	the release of electrons from parent atoms
	any of several bodily processes by which substances go out of the body
	a substance that is emitted or released