"Tritium. It decays into deturium relatively quickly."
Worse, it decays into helium--and helium captures neutrons very efficiently, so that only a little helium can cause the weapon to not generate a significant yield.
Sorry, but no. Helium neutron capture cross-section is very low. That's one of the reasons they use it as primary coolant in carbon-moderated HTGR's (High-Temperature-Gas-Reactors).