Helium

Helium

He
In situ availability:	trace
Necessity:
Atomic number:	2
Atomic mass:	4.002602
group:	18
period:	1
normal phase:	Gas
series:	Noble gases
density:	0.1786 g/L
melting point:	0.95K, -272.2°C, -458.0°F
boiling point:	4.22K, -268.93°C, -452.07°F
N/A ← N/A → N/A
H ← He → Li
F ← Ne → N/A
Atomic radius (pm):	31 pm
Bohr radius (pm):
Covalent radius (pm):	32
Van der Waals radius (pm):	140
ionic radius (pm):	-
1st ion potential (eV):	24.59
Electron Configuration
1s²
Electrons Per Shell
2
Electronegativity:
Electron Affinity:	Unstable anion
Oxidation states:	-
Magnetism:
Crystal structure:	Hexagonal or body centered cubic

Helium is a component of the solar wind, and hence is one of the volatiles found (in parts per million level) in Lunar regolith. It is a Noble gas in group 18 and is the second element in the Periodic Table of the Elements. This element has two stable isotopes: 3 and 4.

The most common isotope, Helium-4, has a nucleus of two protons and two neutrons, and two electrons. The less common isotope Helium-3 has two protons and one neutron.

³He

Helium 3 is a rare isotope of the element Helium, consisting of a nucleus with two protons and one neutron. The approved abbreviation (for physics use) for Helium-3 is ³He, however, the abbreviation He3 is also seen. Since most of the Earth's helium is produced by alpha-decay of Uranium isotopes, resulting in ⁴He (the most common isotope of Helium), ³He is rare on Earth. It is comparatively more abundant in non-terrestrial sources, although even in non-terrestrial sources, only a small fraction of helium atoms are Helium 3. The Moon is a source of ³He, which is implanted into the lunar regolith by the solar wind. Helium is present in the soil in quantities of ten to a hundred (weight) parts per million, and 0.003 to 1 percent of this amount (depending on soil) is ³He.

Helium 3 as a Fusion Reaction Fuel

It has been proposed that ³He might be a possible fuel for a Nuclear Fusion reactor to produce energy using the nuclear reaction:

²D + ³He --> ⁴He + ¹H

This reaction has the advantage over the more-commonly proposed D-T fusion reaction that the reaction produces only charged particles (an alpha particle and a proton), with no production of neutrons. However, the corresponding difficulty is that the D-³He reaction has an ignition barrier that is twice as high as the barrier to igniting D-T fusion, because of the fact that the Helium nucleus has twice the charge of a Tritium nucleus. Gerald Kulcinski's group at the Fusion Technology Institute of the University of Wisconsin-Madison has operated an experimental He3 fusion reactor for an extended period, on a non-governmental research budget ^[1], however the reactor has not achieved energy balance or breakeven. So far, D-³He fusion has not yet demonstrated net energy production ("break even"). The development of commercial He3 reactors is dependent upon demonstrating "break even."

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