<P> Helium - 3 occurs as a primordial nuclide, escaping from the Earth's crust into the atmosphere and into outer space over millions of years . Helium - 3 is also thought to be a natural nucleogenic and cosmogenic nuclide, one produced when lithium is bombarded by natural neutrons, which can be released by spontaneous fission and by nuclear reactions with cosmic rays . Some of the helium - 3 found in the terrestrial atmosphere is also a relic of atmospheric and underwater nuclear weapons testing . </P> <P> Much speculation has been made over the possibility of helium - 3 as a future energy source . Unlike most other nuclear fusion reactions, the fusion of helium - 3 atoms releases large amounts of energy without causing the surrounding material to become radioactive . However, the temperatures required to achieve helium - 3 fusion reactions are much higher than in traditional fusion reactions . </P> <P> The abundance of helium - 3 is thought to be greater on the Moon than on Earth, having been embedded in the upper layer of regolith by the solar wind over billions of years, though still lower in abundance than in the solar system's gas giants . </P> <P> Because of its low atomic mass of 3.02 atomic mass units, helium - 3 has some physical properties different from those of helium - 4, with a mass of 4.00 atomic mass units . Because of the weak, induced dipole--dipole interaction between the helium atoms, their microscopic physical properties are mainly determined by their zero - point energy . Also, the microscopic properties of helium - 3 cause it to have a higher zero - point energy than helium - 4 . This implies that helium - 3 can overcome dipole--dipole interactions with less thermal energy than helium - 4 can . </P>

Where is helium 3 found on the moon