Well, Tritium is just a weak beta-emitter, with a relatively short half-life of 12.something years, but if you want to set off a big fusion reaction, Tritium is what you want, if you can get enough of it together.
In H-bombs, they mainly used Deturium, in the form of Lithium Deturide. For fusion, it's not as good as Tritium, but it still fuses better than just regular single-proton Hydrogen, which is nearly impossible tu fuse unless you've got the core of a star squashing it. Deturium can be separated away from the regular hydrogen in water, and it dosent' decay like Tritium. The H-bomb designs used a smaller amount of Tritium in it kind of as an "accelerant", plus the "conventional" fission-bomb trigger to get everything hot and compressed enough for just a milisecond to get it to fuse and set of the really big boom.
There's tons and tons of work involved, and Tritium can't go critical like the heavy transuranic elements no matter how much you bring together, but if you actualy managed to get a significant amount of Tritium together in one place, Uncle Sam would definielty like to know about it..
