nucleon number vs mass number

nucleon number and mass number both are nouns.

Word	Noun	Adjective	Verb	Adverb
nucleon number	Yes	No	No	No
mass number	Yes	No	No	No

As nouns, nucleon number and mass number are synonyms defined as:

nucleon number and mass number: the sum of the number of neutrons and protons in an atomic nucleus

nucleon number (noun)	mass number (noun)
the sum of the number of neutrons and protons in an atomic nucleus	the sum of the number of neutrons and protons in an atomic nucleus