atomic bomb vs plutonium bomb

atomic bomb

noun
  • The possession of one or more atomic bombs; the ability to launch a nuclear attack. 

  • A nuclear weapon that obtains its destructive energy from nuclear fission. 

plutonium bomb

noun
  • A plutonium-fired nuclear bomb. 

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