There's also the intermediate case of boosted fission, where tritium gas is introduced into the fission core, generating neutrons via fusion, that in turn accel

There's also the intermediate case of boosted fission, where tritium gas is introduced into the fission core, generating neutrons via fusion, that in turn accelerate/enhance the fission process (e.g. allowing more fission energy to be released in the interval between detonation and when the device blows itself apart).