fission bomb vs thermonuclear

fission bomb

noun
  • An atomic bomb that uses nuclear fission as a source of energy 

thermonuclear

noun
  • A thermonuclear weapon. 

adj
  • Of, or relating to the use of atomic weapons based on such fusion, especially as distinguished from those based on fission. 

  • Of, or relating to the fusion of atomic nuclei at high temperatures. 

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