Helium-3
Isotope
Helium-3 is a light, stable isotope of helium with two protons and one neutron. Other than protium, helium-3 is the only stable isotope of any element with more protons than neutrons. Helium-3 was discovered in 1939. Wikipedia
Protons: 2
Abundance: 0.000137%
Half-life (t1/2): stable
Parent isotopes: 3H (beta decay of tritium)
Spin: 1⁄2