debriefing vs investigation

debriefing

noun
  • The report of a mission or project, or the information so obtained. 

  • The act of debriefing, or the state of being debriefed. 

investigation

noun
  • The act of investigating; the process of inquiring into or following up; research, especially patient or thorough inquiry or examination 

How often have the words debriefing and investigation occurred in a corpus of books? (source: Google Ngram Viewer )