atomic physics vs cross section

atomic physics and cross section both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic physics	Yes	No	No	No
cross section	Yes	No	No	No

atomic physics (noun)	cross section (noun)
the branch of physics that studies the internal structure of atomic nuclei	(physics) the probability that a particular interaction (as capture or ionization) will take place between particles; measured in barns
	a sample meant to be representative of a whole population
	a section created by a plane cutting a solid perpendicular to its longest axis