text: Some researchers have examined the use of antimatter as an alternative fusion trigger, mainly in the context of antimatter-catalyzed nuclear pulse propulsion but also nuclear weapons. Such a system, in a weapons context, would have many of the desired properties of a pure fusion weapon. The technical barriers to producing and containing the required quantities of antimatter appear formidable, well beyond present capabilities.
  Induced gamma emission is another approach that is currently being researched. Very high energy-density chemicals such as ballotechnics and others have also been suggested as a means of triggering a pure fusion weapon. 
  Nuclear isomers have also been investigated for use in pure fusion weaponry. Hafnium and tantalum isomers can be induced to emit very strong gamma radiation. Gamma emission from these isomers may have enough energy to start a thermonuclear reaction, without requiring any fissile material.