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Helium-3

Helium-3

Overview
Helium-3 is a light, non-radioactive isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 with two proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s and one neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

. It is rare on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, and is sought for use in nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 research. The abundance of helium-3 is thought to be greater on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 (embedded in the upper layer of regolith
Lunar soil
Lunar soil is the fine fraction of the regolith found on the surface of the Moon. Its properties can differ significantly from those of terrestrial soil...

 by the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 over billions of years) and the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

's gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

s (left over from the original solar nebula
Solar nebula
In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

), though still low in quantity (28 ppm of lunar regolith is helium-4
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 and from 1 ppb to 50 ppb is helium-3).

The helion
Helion (chemistry)
A helion is a short name for the naked nucleus of helium, a doubly positively charged helium ion. In practice, helion refers to the stable helium-3 nucleus, in opposition to the other stable nucleus helium-4, which is usually referred to as an alpha particle...

, the nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

 of a helium-3 atom, consists of two protons but only one neutron, in contrast to two neutrons in ordinary helium.
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Encyclopedia
Helium-3 is a light, non-radioactive isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 with two proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s and one neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

. It is rare on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, and is sought for use in nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 research. The abundance of helium-3 is thought to be greater on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 (embedded in the upper layer of regolith
Lunar soil
Lunar soil is the fine fraction of the regolith found on the surface of the Moon. Its properties can differ significantly from those of terrestrial soil...

 by the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 over billions of years) and the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

's gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

s (left over from the original solar nebula
Solar nebula
In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

), though still low in quantity (28 ppm of lunar regolith is helium-4
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 and from 1 ppb to 50 ppb is helium-3).

The helion
Helion (chemistry)
A helion is a short name for the naked nucleus of helium, a doubly positively charged helium ion. In practice, helion refers to the stable helium-3 nucleus, in opposition to the other stable nucleus helium-4, which is usually referred to as an alpha particle...

, the nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

 of a helium-3 atom, consists of two protons but only one neutron, in contrast to two neutrons in ordinary helium. Its existence was first proposed in 1934 by the Australian nuclear physicist Mark Oliphant
Mark Oliphant
Sir Marcus 'Mark' Laurence Elwin Oliphant, AC, KBE, FRS was an Australian physicist and humanitarian who played a fundamental role in the first experimental demonstration of nuclear fusion and also the development of the atomic bomb.During his retirement, Oliphant was appointed as the Governor of...

 while based at Cambridge University
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...

's Cavendish Laboratory
Cavendish Laboratory
The Cavendish Laboratory is the Department of Physics at the University of Cambridge, and is part of the university's School of Physical Sciences. It was opened in 1874 as a teaching laboratory....

, in an experiment in which fast deuterons were reacted with other deuteron targets (the first demonstration of nuclear fusion).

Helium-3 was postulated to be a radioactive isotope until helions from it were identified in a sample of natural helium (which is mostly helium-4) from both the atmosphere and gas well sources, by Luis W. Alvarez and Robert Cornog
Robert Cornog
Robert Alden Cornog , was a physicist and engineer who helped develop the atomic bomb and missile systems from the Snark to the Minuteman....

 in a cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...

 experiment at the Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory
The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...

, in 1939. Although helium-3 was found to be about 10,000 times more rare with respect to helium-4 in helium from wells, its significant presence in underground gas deposits implied that it either did not decay, or else had an extremely long half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 compatible with a primordial isotope.

Helium-3 occurs as primordial nuclide, escaping from the Earth's crust into the atmosphere and into space, over time. It is also a natural nucleogenic
Nucleogenic
A nucleogenic isotope or nuclide, is one that is produced by a natural terrestrial nuclear reaction, other than a reaction beginning with cosmic rays . The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutron...

 and cosmogenic nuclide
Cosmogenic nuclide
See also Environmental radioactivity#NaturalCosmogenic nuclides are rare isotopes created when a high-energy cosmic ray interacts with the nucleus of an in situ solar system atom, causing cosmic ray spallation...

, produced when lithium is bombarded by natural neutrons generated by spontaneous fission, and by cosmic rays. Some helium-3 in the atmosphere is also a relic of open air thermonuclear weapon testing. Tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

, with a roughly 12-year half-life, decays into helium-3, which can be recovered. Irradiation
Irradiation
Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve a specific purpose, rather than radiation exposure to...

 of lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 in a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

—either a fusion or fission reactor—can also produce tritium, and thus (after decay) helium-3.

Helium-3 is proposed as a second-generation fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 fuel for fusion power uses, but such systems are still in very early experimental development phases. Helium-3 is used in neutron detection, and extremely low temperature cryogenics. It has been used as a magnetizable (hyperpolarized
Hyperpolarization (physics)
Hyperpolarization is the nuclear spin polarization of a material far beyond thermal equilibrium conditions. It is commonly applied to gases such as 129Xe and 3He which are then used, for instance, in hyperpolarized magnetic resonance imaging of the lungs....

) gas to carry out nuclear magnetic imaging studies of the lungs.

Physical properties


Owing to its lower atomic mass (3.0160293 amu
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...

), helium-3 has significantly different properties from helium-4 (4.0026 amu). Because of the weak, induced dipole-dipole interaction between helium atoms, their physical properties are mainly determined by zero point energy (groundstate kinetic energy), and the properties of helium-3 cause it to have higher zero point energy, which means helium-3 can overcome dipole-dipole interaction with less thermal energy than helium-4. Helium-3 boils at 3.19 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

 compared to helium-4's 4.23 K, and its critical point
Critical point (thermodynamics)
In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions at which a phase boundary ceases to exist...

 is also lower at 3.35 K, compared to helium-4's 5.19 K. It has less than half the density when liquid at its boiling point: 0.059 g/ml compared to helium-4's 0.12473 g/ml at one atmosphere. Its latent heat of vaporization is also considerably lower at 0.026 kJ/mol compared to helium-4's 0.0829 kJ/mol.

Fusion reactions

Comparison of neutronicity of reactions
Reactants Products Q n/MeV
First-generation fusion fuels
21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 (D-D)
32He + 10n 3.268 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0.306
21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 (D-D)
31H
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 + 11p
4.032 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0
21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 31H
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 (D-T)
42He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 + 10n
17.571 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0.057
Second-generation fusion fuel
21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 32He (D-3He)
42He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 + 11p
18.354 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0
Third-generation fusion fuels
32He + 32He 42He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

+ 211p
12.86 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0
115B + 11p 3 42He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

8.68 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0
Net result of D burning (sum of first 4 rows)
6D 2(4He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 + n + p)
43.225 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0.046
Current nuclear fuel
235U
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

 + n
2 FP
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

+ 2.5n
~200 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...

0.001


Some fusion processes produce highly energetic neutrons which render reactor components radioactive with activation product
Activation product
Activation products are materials made radioactive by neutron activation.Fission products and actinides produced by neutron absorption of nuclear fuel itself are normally referred to by those specific names, and activation product reserved for products of neutron capture by other materials, such as...

s through the continuous bombardment of the reactor's components with emitted neutrons. Because of this bombardment and irradiation, power generation must occur indirectly through thermal means, as in a fission reactor. However, the appeal of helium-3 fusion stems from the aneutronic
Aneutronic fusion
Aneutronic fusion is any form of fusion power where neutrons carry no more than 1% of the total released energy. The most-studied fusion reactions release up to 80% of their energy in neutrons...

 nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

, can be contained using electric and magnetic fields. The momentum energy of this proton (created in the fusion process) will interact with the containing electromagnetic field, resulting in direct net electricity generation.

Because of the higher Coulomb barrier
Coulomb barrier
The Coulomb barrier, named after Coulomb's law, which is named after physicist Charles-Augustin de Coulomb , is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a nuclear reaction...

, the temperatures required for 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 32He fusion are much higher than those of conventional 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 31H
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 (deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

) fusion. Moreover, since both reactants need to be mixed together to fuse, reactions between nuclei of the same reactant will occur, and the D-D reaction (21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

) does produce a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

. Reaction rates vary with temperature, but the D-3He reaction rate is never greater than 3.56 times the D-D reaction rate (see graph). Therefore fusion using D-3He fuel may produce a somewhat lower neutron flux than D-T fusion, but is by no means clean, negating some of its main attraction.

A second possibility, fusing 32He with itself (32He + 32He), requires even higher temperatures (since now both reactants have a +2 charge), and thus is even more difficult than the D-3He reaction. However, it does offer a possible reaction that produces no neutrons; the protons it produces possess charges and can be contained using electric and magnetic fields, which in turn results in direct electricity generation. 32He + 32He fusion has been demonstrated in the laboratory and is thus theoretically feasible and would have immense advantages, but commercial viability is many years in the future.

The amounts of helium-3 needed as a replacement for conventional fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s are substantial by comparison to amounts currently available. The total amount of energy produced in the 21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 + 32He reaction is 18.4 MeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...

, which corresponds to some 493 megawatt-hour
Watt-hour
The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...

s (4.93×108 W·h) per three gram
Gram
The gram is a metric system unit of mass....

s (one mole) of ³He. Even if that total amount of energy could be converted to electrical power with 100% efficiency (a physical impossibility), it would correspond to about 30 minutes of output of a gigawatt electrical plant; a year's production by the same plant would require some 17.5 kilograms of helium-3.

The amount of fuel needed for large-scale applications can also be put in terms of total consumption: According to the US Energy Information Administration, "Electricity consumption by 107 million U.S. households in 2001 totaled 1,140 billion kW·h" (1.14×1015 W·h). Again assuming 100% conversion efficiency, 6.7 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s of helium-3 would be required for that segment of the energy demand of the United States, 15 to 20 tonnes given a more realistic end-to-end conversion efficiency.

Neutron detection


Helium-3 is a most important isotope in instrumentation for neutron detection
Neutron detection
Neutron detection is the effective detection of neutrons entering a well-positioned detector. There are two key aspects to effective neutron detection: hardware and software. Detection hardware refers to the kind of neutron detector used and to the electronics used in the detection setup...

. It has a high absorption cross section for thermal neutron
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...

 beams and is used as a converter gas in neutron detectors. The neutron is converted through the nuclear reaction
n + 3He → 3H + 1H + 0.764 MeV

into charged particles tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 (T, 3H) and protium
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force...

 (p, 1H) which then are detected by creating a charge cloud in the stopping gas of a proportional counter
Proportional counter
A proportional counter is a measurement device to count particles of ionizing radiation and measure their energy.A proportional counter is a type of gaseous ionization detector. Its operation is similar to that of a Geiger-Müller counter, but uses a lower operating voltage. An inert gas is used to...

 or a Geiger-Müller tube
Geiger-Müller tube
A Geiger–Müller tube is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each. It was named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with Geiger in...

.

Furthermore, the absorption process is strongly spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...

-dependent, which allows a spin-polarized
Spin polarization
Spin polarization is the degree to which the spin, i.e., the intrinsic angular momentum of elementary particles, is aligned with a given direction. This property may pertain to the spin, hence to the magnetic moment, of conduction electrons in ferromagnetic metals, such as iron, giving rise to...

 helium-3 volume to transmit neutrons with one spin component while absorbing the other. This effect is employed in neutron polarization analysis, a technique which probes for magnetic properties of matter.

The United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 Department of Homeland Security had hoped to deploy detectors to spot smuggled plutonium in shipping containers by their neutron emissions, but the worldwide shortage of helium-3 following the draw down in nuclear weapons production since the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

 has to some extent prevented this.

Cryogenics


A helium-3 refrigerator
Helium-3 refrigerator
A helium-3 refrigerator is a simple device used in experimental physics for obtaining temperatures down to about 0.2 kelvins. By evaporative cooling of helium-4 , a 1-K pot liquefies a small amount of helium-3 in a small vessel called a helium-3 pot...

 uses helium-3 to achieve temperatures of 0.2 to 0.3 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

. A dilution refrigerator
Dilution refrigerator
A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4...

 uses a mixture of helium-3 and helium-4 to reach cryogenic
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...

 temperatures as low as a few thousandths of a kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

.

An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a fermion
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....

 since it contains an odd number of spin 1/2 particles. Helium-4 nuclei are boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....

s, containing an even number of spin 1/2 particles. This is a direct result of the addition rules for quantized angular momentum. At low temperatures (about 2.17 K), helium-4 undergoes a phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

: A fraction of it enters a superfluid
Superfluid
Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...

 phase
Phase (matter)
In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

 that can be roughly understood as a type of Bose-Einstein condensate. Such a mechanism is not available for helium-3 atoms, which are fermions. However, it was widely speculated that helium-3 could also become a superfluid at much lower temperatures, if the atoms formed into pairs analogous to Cooper pair
Cooper pair
In condensed matter physics, a Cooper pair or BCS pair is two electrons that are bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Cooper...

s in the BCS theory
BCS theory
BCS theory — proposed by Bardeen, Cooper, and Schrieffer in 1957 — is the first microscopic theory of superconductivity since its discovery in 1911. The theory describes superconductivity as a microscopic effect caused by a "condensation" of pairs of electrons into a boson-like state...

 of superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

. Each Cooper pair, having integer spin, can be thought of as a boson. During the 1970s, David Lee
David Lee (physicist)
David Morris Lee is an American physicist who shared the 1996 Nobel Prize in Physics with Robert C. Richardson and Douglas Osheroff "for their discovery of superfluidity in helium-3"-Personal life:...

, Douglas Osheroff and Robert Coleman Richardson
Robert Coleman Richardson
Robert Coleman Richardson is an American experimental physicist whose area of research includes sub-millikelvin temperature studies of helium-3...

 discovered two phase transitions along the melting curve, which were soon realized to be the two superfluid phases of helium-3. The transition to a superfluid occurs at 2.491 millikelvins (i.e., 0.002491 K) on the melting curve. They were awarded the 1996 Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...

 for their discovery. Tony Leggett
Anthony James Leggett
Sir Anthony James Leggett, KBE, FRS , aka Tony Leggett, has been a Professor of Physics at the University of Illinois at Urbana-Champaign since 1983....

 won the 2003 Nobel Prize in Physics for his work on refining understanding of the superfluid phase of helium-3.

In zero magnetic field, there are two distinct superfluid phases of 3He, the A-phase and the B-phase. The B-phase is the low-temperature, low-pressure phase which has an isotropic energy gap. The A-phase is the higher temperature, higher pressure phase that is further stabilized by a magnetic field and has two point nodes in its gap. The presence of two phases is a clear indication that 3He is an unconventional superfluid (superconductor), since the presence of two phases requires an additional symmetry, other than gauge symmetry, to be broken. In fact, it is a p-wave superfluid, with spin one, S=1, and angular momentum one, L=1. The ground state corresponds to total angular momentum zero, J=S+L=0 (vector addition). Excited states are possible with non-zero total angular momentum, J>0, which are excited pair collective modes. Because of the extreme purity of superfluid 3He (since all materials except 4He have solidified and
sunk to the bottom of the liquid 3He and any 4He has phase separated entirely, this is the most pure condensed matter state), these collective modes have been studied with much greater precision than in any other unconventional pairing system.

Medical lung imaging


The nuclei of some atoms (such as helium-3, but not helium-4) have an intrinsic spin. In a magnetized (or "polarized") gas, these spins can be lined up in the same direction, by various means. After this, like gyroscopes, the nuclei continue to spin with their axes pointed toward one direction in space, regardless of the direction of changing motions of the gas atoms that contain them.

Polarized (also referred to as hyperpolarized
Hyperpolarization (physics)
Hyperpolarization is the nuclear spin polarization of a material far beyond thermal equilibrium conditions. It is commonly applied to gases such as 129Xe and 3He which are then used, for instance, in hyperpolarized magnetic resonance imaging of the lungs....

) helium-3 gas may be produced directly, using lasers of the appropriate frequency. With the use of a thin layer of protective caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

 metal on the inside of gas cylinders, the magnetized gas may then be stored at pressures of 10 atm, for up to 100 hours. When inhaled, mixtures containing the gas can be imaged with an MRI-like scanner which produces breath-by-breath images of lung ventilation, in real-time. Applications of this experimental technique are just beginning to be explored.

Production


Current US industrial consumption of Helium-3 is approximately 60,000 liters per year; cost at auction has typically been approximately $100/liter although increasing demand has raised prices to as much as $2,000/liter in recent years. Helium-3 is naturally present in small quantities due to radioactive decay, but virtually all helium-3 used in industry is manufactured. Helium-3 is a product of tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

 decay, and tritium can be produced through neutron bombardment of deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

, lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

, boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

, or nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 targets. Production of tritium in significant quantities requires the high neutron flux of a nuclear reactor; breeding tritium with lithium-6 consumes the neutron, while breeding with lithium-7 produces a low energy neutron as a replacement for the consumed fast neutron.

Current supplies of helium-3 come, in part, from the dismantling of nuclear weapons where it accumulates, however the need for warhead disassembly is diminishing. Consequently tritium itself is in short supply, and the US Department of Energy recently began producing it by the lithium irradiation method at the Tennessee Valley Authority's Watts Bar reactor. Substantial quantities of tritium could also be extracted from the heavy water coolant in CANDU nuclear reactors.

Production of helium-3 from tritium at a rate sufficient to meet world demand will require significant investment, as tritium must be produced at the same rate as helium-3, and approximately eighteen times as much tritium must be maintained in storage as the amount of helium-3 produced annually by decay (production rate dN/dt from number of moles or other unit mass of tritium N, is N γ = N ln 2/t½ where the value of t½/(ln 2) is about 18 years; see radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

). If commercial fusion reactors were to use helium-3 as a fuel, they would require tens of tonnes of helium-3 each year to produce a fraction of the world's power, requiring substantial expansion of facilities for tritium production and storage.

Solar nebula (primordial) abundance


One early estimate of the primordial ratio of 3He to 4He in the solar nebula has been the measurement of their ratio in the atmosphere of Jupiter, measured by mass spectrometer of the Galileo atmospheric entry probe. This ratio is about 1:10,000, or 100 parts of 3He per million parts of 4He. This is roughly the same ratio of the isotopes in lunar regolith, when it contains 28 ppm helium-4 and 2.8 ppb helium-3 (which is at the lower end of actual sample measurements, which vary from about 1.4 to 15 ppb). However, terrestrial ratios of the isotopes are lower by a factor of 100, mainly due to enrichment of helium-4 stocks in the mantle by billions of years of alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...

 from uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

.

Terrestrial abundance


3He is a primordial substance in the Earth's mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

, considered to have become entrapped within the Earth during planetary formation. The ratio of 3He to 4He within the Earth's crust and mantle is less than that for assumptions of solar disk composition as obtained from meteorite and lunar samples, with terrestrial materials generally containing lower 3He/4He ratios due to ingrowth of 4He from radioactive decay.

3He is present within the mantle, in the ratio of 200–300 parts of 3He to a million parts of 4He. Ratios of 3He/4He in excess of atmospheric are indicative of a contribution of 3He from the mantle. Crustal sources are dominated by the 4He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 which is produced by the decay of radioactive elements in the crust and mantle.

The ratio of Helium-3 to Helium-4 in natural Earth-bound sources varies greatly. Samples of the ore Spodumene
Spodumene
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl2, and is a source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite , yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size...

 from Edison Mine, South Dakota were found to contain 12 parts of helium-3 to a million parts of helium-4. Samples from other mines showed 2 parts per million.

Helium is also present as up to 7% of some natural gas sources, and large sources have over 0.5% (above 0.2% makes it viable to extract). Algeria's annual gas production is assumed to contain 100 million normal cubic metres and this would contain between 5 and 50 m3 of Helium-3 (about 1 to 10 kilograms) using the normal abundance range of 0.5 to 5 ppm. Similarly the US 2002 stockpile of 1 billion normal m3 would have contained about 10 to 100 kilograms of helium-3.

3He is also present in the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. The natural abundance of 3He in naturally occurring helium gas is 1.38 (1.38 parts per million). The partial pressure of helium in the Earth's atmosphere is about 0.52 Pa, and thus helium accounts for 5.2 parts per million of the total pressure (101325 Pa) in the Earth's atmosphere, and 3He thus accounts for 7.2 parts per trillion of the atmosphere. Since the atmosphere of the Earth has a mass of about 5.14 tonnes, the mass of 3He in the Earth's atmosphere is the product of these numbers, or about 37,000 tonnes of 3He.

3He is produced on Earth from three sources: lithium spallation
Spallation
In general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection or vaporization of material from a target during impact by a projectile...

, cosmic rays, and beta decay of tritium (3H). The contribution from cosmic rays is negligible within all except the oldest regolith materials, and lithium spallation reactions are a lesser contributor than the production of 4He by alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

 emissions.

The total amount of helium-3 in the mantle may be in the range of 0.1–1 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s. However, most of the mantle is not directly accessible. Some helium-3 leaks up through deep-sourced hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...

 volcanoes such as those of the Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

an islands, but only 300 grams per year is emitted to the atmosphere. Mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

s emit another 3 kilogram per year. Around subduction zone
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

s, various sources produce helium-3 in natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 deposits which possibly contain a thousand tonnes of helium-3 (although there may be 25 thousand tonnes if all ancient subduction zones have such deposits). Wittenberg estimated that United States crustal natural gas sources may have only half a tonne total. Wittenberg cited Anderson's estimate of another 1200 metric tonnes in interplanetary dust particles on the ocean floors. In the 1994 study, extracting helium-3 from these sources consumes more energy than fusion would release. Wittenberg also writes that extraction from US crustal natural gas, consumes ten times the energy available from fusion reactions.

Extraterrestrial supplies


Materials on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

's surface contain helium-3 at concentrations on the order of between 1.4 and 15 ppb
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...

 in sunlit areas, and may contain concentrations as much as 50 ppb
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...

 in permanently shadowed regions. A number of people, starting with Gerald Kulcinski in 1986, have proposed to explore the moon
Exploration of the Moon
The physical exploration of the Moon began when Luna 2, a space probe launched by the Soviet Union, made an impact on the surface of the Moon on September 14, 1959. Prior to that the only available means of exploration had been observation. The invention of the optical telescope brought about the...

, mine lunar regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

 and use the helium-3 for fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

. Because of the low concentrations of helium-3, any mining equipment would need to process extremely large amounts of regolith (over 100,000 million tonnes of regolith to obtain one ton of helium 3), and some proposals have suggested that helium-3 extraction be piggybacked onto a larger mining and development operation.

The primary objective of Indian Space Research Organization's first lunar probe called Chandrayaan-I, launched on October 22, 2008, was reported in some sources to be mapping the Moon's surface for helium-3-containing minerals. However, this is debatable; no such objective is mentioned in the project's official list of goals, while at the same time, many of its scientific payloads have noted helium-3-related applications.

Cosmochemist
Cosmochemistry
Cosmochemistry or chemical cosmology is the study of the chemical composition of matter in the universe and the processes that led to those compositions. This is done primarily through the study of the chemical composition of meteorites and other physical samples...

 and geochemist Ouyang Ziyuan
Ouyang Ziyuan
Ouyang Ziyuan is a Chinese cosmochemist, geochemist and space advocate. He is a research professor at the Institute of Geochemistry of the Chinese Academy of Sciences.-Geochemical career:...

 from the Chinese Academy of Sciences
Chinese Academy of Sciences
The Chinese Academy of Sciences , formerly known as Academia Sinica, is the national academy for the natural sciences of the People's Republic of China. It is an institution of the State Council of China. It is headquartered in Beijing, with institutes all over the People's Republic of China...

 who is now in charge of the Chinese Lunar Exploration Program
Chang'e program
Chang’e 1 was an unmanned Chinese lunar-orbiting spacecraft, part of the first phase of the Chinese Lunar Exploration Program. The spacecraft was named after the Chinese Moon goddess, Chang'e....

 has already stated on many occasions that one of the main goals of the program would be the mining of helium-3, from which operation "each year three space shuttle missions could bring enough fuel for all human beings across the world." which is an extreme overstatement however, as one payload to GTO
Geostationary transfer orbit
A geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....

 of current spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 designs is less than 4 tonnes. To "bring enough fuel for all human beings across the world", more than one Space Shuttle load (and the processing of 4 million tonnes of regolith) per week would be necessary.

In January 2006, the Russian space company RKK Energiya announced that it considers lunar helium-3 a potential economic resource to be mined by 2020, if funding can be found.

Mining gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

s for helium-3 has also been proposed. The British Interplanetary Society
British Interplanetary Society
The British Interplanetary Society founded in 1933 by Philip E. Cleator, is the oldest space advocacy organisation in the world whose aim is exclusively to support and promote astronautics and space exploration.-Structure:...

's hypothetical Project Daedalus
Project Daedalus
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible unmanned interstellar spacecraft. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use current or near-future technology and had to...

 interstellar probe design was fueled by helium-3 mines in the atmosphere of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, for example. Jupiter's high gravity makes this a less energetically favorable operation than extracting helium-3 from the other gas giants of the solar system, however.

Despite the many proposals, the limited advantages helium-3 provides for controlled fusion, the complex infrastructure required for lunar extraction, and the relatively modest cost of terrestrial production make it unlikely that extraterrestrial mining of helium-3 will ever be practical.

Power generation


A second-generation approach to controlled fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 power involves combining helium-3 (32He) and deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 (21H
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

). This reaction produces a helium-4
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 ion (42He
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

) (like an alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

, but of different origin) and a high-energy proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

 (positively charged hydrogen ion) (11p). The most important potential advantage of this fusion reaction for power production as well as other applications lies in its compatibility with the use of electrostatic fields to control fuel ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s and the fusion protons. Protons, as positively charged particles, can be converted directly into electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

, through use of solid-state
Solid-state chemistry
Solid-state chemistry, also sometimes referred to as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials, particularly, but not necessarily exclusively of, non-molecular solids...

 conversion materials as well as other techniques. Potential conversion efficiencies of 70% may be possible, as there is no need to convert proton energy to heat in order to drive a turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

-powered electrical generator.

There have been many claims about the capabilities of helium-3 power plants. According to proponents, fusion power plants operating on deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 and helium-3 would offer lower capital and operating cost
Operating cost
Operating costs can be described as the expenses which are related to the operation of a business, or to the operation of a device, component, piece of equipment or facility.-Business operating costs:...

s than their competitors due to less technical complexity, higher conversion efficiency, smaller size, the absence of radioactive fuel, no air or water pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

, and only low-level radioactive waste disposal requirements. Recent estimates suggest that about $6 billion in investment
Investment
Investment has different meanings in finance and economics. Finance investment is putting money into something with the expectation of gain, that upon thorough analysis, has a high degree of security for the principal amount, as well as security of return, within an expected period of time...

 capital
Capital (economics)
In economics, capital, capital goods, or real capital refers to already-produced durable goods used in production of goods or services. The capital goods are not significantly consumed, though they may depreciate in the production process...

 will be required to develop and construct the first helium-3 fusion power plant. Financial breakeven at today's wholesale electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 prices (5 US cents per kilowatt-hour) would occur after five 1-gigawatt plants were on line, replacing old conventional plants or meeting new demand.

The reality is not so clear-cut. The most advanced fusion programs in the world are inertial confinement fusion
Inertial confinement fusion
Inertial confinement fusion is a process where nuclear fusion reactions are initiated by heating and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium....

 (such as National Ignition Facility
National Ignition Facility
The National Ignition Facility, or NIF is a large, laser-based inertial confinement fusion research device located at the Lawrence Livermore National Laboratory in Livermore, California. NIF uses powerful lasers to heat and compress a small amount of hydrogen fuel to the point where nuclear fusion...

) and magnetic confinement fusion
Magnetic confinement fusion
Magnetic confinement fusion is an approach to generating fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach is...

 (such as ITER
ITER
ITER is an international nuclear fusion research and engineering project, which is currently building the world's largest and most advanced experimental tokamak nuclear fusion reactor at Cadarache in the south of France...

 and other tokamak
Tokamak
A tokamak is a device using a magnetic field to confine a plasma in the shape of a torus . Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape...

s). In the case of the former, there is no solid roadmap to power generation. In the case of the latter, commercial power generation is not expected until around 2050. In both cases, the type of fusion discussed is the simplest: D-T fusion. The reason for this is the very low Coulomb barrier
Coulomb barrier
The Coulomb barrier, named after Coulomb's law, which is named after physicist Charles-Augustin de Coulomb , is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a nuclear reaction...

 for this reaction; for D+3He, the barrier is much higher, and it is even higher for 3He–3He. The immense cost of reactors like ITER
ITER
ITER is an international nuclear fusion research and engineering project, which is currently building the world's largest and most advanced experimental tokamak nuclear fusion reactor at Cadarache in the south of France...

 and National Ignition Facility
National Ignition Facility
The National Ignition Facility, or NIF is a large, laser-based inertial confinement fusion research device located at the Lawrence Livermore National Laboratory in Livermore, California. NIF uses powerful lasers to heat and compress a small amount of hydrogen fuel to the point where nuclear fusion...

 are largely due to their immense size, yet to scale up to higher plasma temperatures would require reactors far larger still. The 14.7 MeV proton and 3.6 MeV alpha particle from D–3He fusion, plus the higher conversion efficiency, means that more electricity is obtained per kilogram than with D-T fusion (17.6 MeV), but not that much more. As a further downside, the rates of reaction for helium-3 fusion reactions are not particularly high, requiring a reactor that is larger still or more reactors to produce the same amount of electricity.

To attempt to work around this problem of massively large power plants that may not even be economical with D-T fusion, let alone the far more challenging D–3He fusion, a number of other reactors have been proposed – the Fusor
Fusor
The Farnsworth–Hirsch fusor, or simply fusor, is an apparatus designed by Philo T. Farnsworth to create nuclear fusion. It has also been developed in various incarnations by researchers including Elmore, Tuck, and Watson, and more recently by George H. Miley and Robert W. Bussard...

, Polywell
Polywell
A polywell device is a type of fusion reactor that was originated by Robert Bussard under a U.S. Navy research contract. It traps electrons in a magnetic confinement inside its hollow center. The negatively charged electrons then accelerate positively charged ions for the purpose of achieving...

, Focus fusion, and many more, though many of these concepts have fundamental problems with achieving a net energy gain, and generally attempt to achieve fusion in thermal disequilibrium, something that could potentially prove impossible, and consequently, these long-shot programs tend to have trouble garnering funding despite their low budgets. Unlike the "big", "hot" fusion systems, however, if such systems were to work, they could scale to the higher barrier "aneutronic
Aneutronic fusion
Aneutronic fusion is any form of fusion power where neutrons carry no more than 1% of the total released energy. The most-studied fusion reactions release up to 80% of their energy in neutrons...

" fuels. However, these systems would scale well enough that their proponents tend to promote p-B fusion, which requires no exotic fuels like helium-3.

In popular culture

  • Helium-3 was harvested in the 2009 science fiction movie Moon
    Moon (film)
    Moon is a 2009 British science fiction drama film about a man who experiences a personal crisis as he nears the end of a three-year solitary stint mining helium-3 on the far side of the Earth's moon. It is the feature debut of director Duncan Jones. Sam Rockwell stars as the employee Sam Bell, and...

    , by the story's protagonist Sam Bell, the occupant of a mining station on the far side of the Moon
    Moon
    The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

    .
  • The isotope is mined from asteroids to be used as fuel for the entire economy in the space combat game Allegiance.
  • Helium-3 is described as a common commercial starship fuel in the science fiction role-playing games Mass Effect
    Mass Effect
    Mass Effect is an action role-playing game developed by BioWare for the Xbox 360 and Microsoft Windows by Demiurge Studios. The Xbox 360 version was released worldwide in November 2007 published by Microsoft Game Studios...

    (2007) and Mass Effect 2
    Mass Effect 2
    Mass Effect 2 is an action role-playing game developed by BioWare and published by Electronic Arts for Microsoft Windows, Xbox 360 and PlayStation 3. The game was released for Microsoft Windows and Xbox 360 on January 26, 2010 and for PlayStation 3 on January 18, 2011...

    (2010), where it is harvested from gas giants.
  • In the Japanese hard science fiction manga
    Manga
    Manga is the Japanese word for "comics" and consists of comics and print cartoons . In the West, the term "manga" has been appropriated to refer specifically to comics created in Japan, or by Japanese authors, in the Japanese language and conforming to the style developed in Japan in the late 19th...

     Planetes
    Planetes
    is a Japanese hard science fiction manga by Makoto Yukimura. It was adapted as a 26-episode television anime by Sunrise, which was broadcast on NHK from October 2003 through April 2004...

    , 70% of the world's energy demands are provided by electricity produced by nuclear fusion, with the main fuel source being helium-3.
  • The isotope was harvested from gas giants by Edenists for use as starship fuel by Adamists in The Night's Dawn Trilogy
    The Night's Dawn Trilogy
    British author Peter F. Hamilton's The Night's Dawn Trilogy consists of three science fiction novels: The Reality Dysfunction , The Neutronium Alchemist , and The Naked God...

    (1996, 1997 and 1999), by British science fiction author Peter F. Hamilton.
  • Mark Anson's science fiction thriller Below Mercury is set in the abandoned workings of Erebus Mine, an ice mining and helium-3 extraction facility in the depths of Chao Meng-fu crater
    Chao Meng-Fu (crater)
    Chao Meng-Fu is a 167 kilometer-diameter crater on Mercury named after the Chinese painter and calligrapher Zhao Mengfu . Due to its location near Mercury's south pole and the planet's small axial tilt, an estimated 40% of the crater lies in permanent shadow...

    , on the South Pole of Mercury.
  • Frank Schätzing talks about the mining of helium-3 in his book Limit, published in march 2011

External links