fissionable vs thermonuclear bomb

fissionable

noun

  • Any fissile or fissionable substance. 

adj

  • Capable of undergoing nuclear fission; fissile. 

thermonuclear bomb

noun

  • Synonym of thermonuclear weapon 

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