Helium-3

Helium isotope with two protons and one neutron

Helium-3 (3He) is a light, stable isotope of helium with two protons and one neutron in a nucleus called a helion. It is in contrast to the more common isotope, helium-4, which has two protons and two neutrons. Helium-3 and hydrogen-1 are the only stable nuclides with more protons than neutrons.

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