High Quality Content by WIKIPEDIA articles! Helium-3 (He-3, sometimes called tralphium) is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research. The abundance of helium-3 is thought to be greater on the Moon (embedded in the upper layer of regolith by the solar wind over billions of years) and the solar system`s gas giants (left over from the original solar nebula), though still low in quantity (28 ppm of lunar regolith is helium-4 and from 1 ppb to 50 ppb is helium-3).