research worker vs investigator

research worker and investigator both are nouns.

Word	Noun	Adjective	Verb	Adverb
research worker	Yes	No	No	No
investigator	Yes	No	No	No

As nouns, research worker and investigator are synonyms defined as:

research worker and investigator: a scientist who devotes himself to doing research

Other synonyms of research worker include researcher.

research worker (noun)	investigator (noun)
a scientist who devotes himself to doing research	someone who investigates
	a scientist who devotes himself to doing research
	a police officer who investigates crimes