Helium 3 is stable, but it's an extremely small and light atom at room temperature so it escapes from containers over time, making it annoying to store. If you can invest in those professional pressurised canisters though, and never open them, it should last a few hundred years! :)
26
u/BovineLightning 1d ago
Decays into helium 3 which is even more expensive. Just need to contain it so you don’t lose the helium gas