Editing Tritium (section)

==== Boosting ====
{{Main|Boosted fission weapon}}
Before detonation, a few grams of tritium–deuterium gas are injected into the hollow "[[pit (nuclear weapon)|pit]]" of fissile material. The early stages of the fission chain reaction supply enough heat and compression to start deuterium–tritium fusion; then both fission and fusion proceed in parallel, the fission assisting the fusion by continuing heating and compression, and the fusion assisting the fission with highly energetic (14.1-[[Electronvolt|MeV]]) neutrons. As the fission fuel depletes and also explodes outward, it falls below the density needed to stay critical by itself, but the fusion neutrons make the fission process progress faster and continue longer than it would without boosting. Increased yield comes overwhelmingly from the increased fission. The energy from the fusion itself is much smaller because the amount of fusion fuel is much smaller. Effects of boosting include:
* increased yield (for the same amount of fission fuel, compared to unboosted)
* the possibility of [[variable yield]] by varying the amount of fusion fuel
* allowing the bomb to require a smaller amount of the very expensive fissile material
* eliminating the risk of predetonation by nearby nuclear explosions
* not so stringent requirements on the implosion setup, allowing for a smaller and lighter amount of high explosives to be used

The tritium in a [[warhead]] is continually undergoing radioactive decay, becoming unavailable for fusion. Also, its [[decay product]], helium-3, absorbs neutrons. This can offset or reverse the intended effect of the tritium, which was to generate many free neutrons, if too much helium-3 has accumulated. Therefore, boosted bombs need fresh tritium periodically. The estimated quantity needed is {{convert|4|g}} per warhead.<ref name=ieer/> To maintain constant levels of tritium, about {{convert|0.20|g}} per warhead per year must be supplied to the bomb.

One [[mole (unit)|mole]] of deuterium-tritium gas contains about {{convert|3.0|g}} of tritium and {{convert|2.0|g}} of deuterium. In comparison, the 20&nbsp;moles of plutonium in a nuclear bomb consists of about {{convert|4.5|kg}} of [[plutonium-239]].