thorium vs thorium-228

thorium and thorium-228 both are nouns.

Word	Noun	Adjective	Verb	Adverb
thorium	Yes	No	No	No
thorium-228	Yes	No	No	No

As nouns, thorium-228 is a hyponym of thorium; that is, thorium-228 is a word with a more specific, narrower meaning than thorium:

thorium: a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands
thorium-228: radioactive isotope of thorium with mass number 228

Other hyponyms of thorium include radiothorium.

thorium (noun)	thorium-228 (noun)
a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands	radioactive isotope of thorium with mass number 228