thorium-228 vs atomic number 90

thorium-228 and atomic number 90 both are nouns.

Word	Noun	Adjective	Verb	Adverb
thorium-228	Yes	No	No	No
atomic number 90	Yes	No	No	No

As nouns, atomic number 90 is a hypernym of thorium-228; that is, atomic number 90 is a word with a broader meaning than thorium-228:

thorium-228: radioactive isotope of thorium with mass number 228
atomic number 90: 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

Other hypernyms of thorium-228 include Th, thorium.

thorium-228 (noun)	atomic number 90 (noun)
radioactive isotope of thorium with mass number 228	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