Tritium Decay to Helium-3

Tritium beta-decays to helium-3 with a 12.32-year half-life, a fixed physical process that turns a tritium inventory into a helium-3 inventory.

The beta decay

Tritium (³H) is unstable. It undergoes beta-minus decay: ³H → ³He + e⁻ + ν̄. A neutron in the tritium nucleus converts to a proton, emitting an electron and an antineutrino, leaving helium-3. The decay energy is low — about 18.6 keV maximum electron energy — so the process is easy to shield and produces no penetrating gamma radiation. The half-life is 12.32 years.

What the half-life implies

A 12.32-year half-life means roughly 5.5% of a tritium inventory converts to helium-3 each year. This is slow and steady — an advantage for supply planning, because the conversion cannot run away or stall. A tritium store put aside today is a predictable helium-3 store tomorrow. It also means helium-3 accumulates whether or not any machine is running, so the breeder can build a helium-3 reserve before the first burner needs it.

• Reaction: ³H → ³He + e⁻ + antineutrino
• Half-life: 12.32 years (~5.5% conversion per year)
• Decay energy low (≤18.6 keV), no gamma emission
• Conversion is passive and predictable — good for inventory planning

This decay is the single physical fact that makes a terrestrial helium-3 supply possible at all. Every other terrestrial source of helium-3 traces back to the same process happening somewhere else.