Template:POV Template:Infobox isotope Helium-3 (He-3) 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 0.01 ppm is helium-3).
The helion, the nucleus 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 while based at Cambridge University's Cavendish Laboratory, in an experiment in which fast deuterons were reacted with other deuteron targets (the first demonstration of nuclear fusion). Helium-3, as an isotope, was postulated to be radioactive, until helions from it were accidentally identified as a trace "contaminant" in a sample of natural helium (which is mostly helium-4) from a gas well, by Luis W. Alvarez and Robert Cornog in a cyclotron experiment at the Lawrence Berkeley National Laboratory, in 1939. The presence of helium-3 in underground gas deposits implied that it either did not decay or had an extremely long half-life compatible with a primordial isotope.
Helium-3 is proposed as a second-generation fusion fuel for fusion power uses. Tritium decays into helium-3 with a 12 year half-life. Tritium produced for other uses evolves helium-3 which can be recovered. Irradiation of lithium in a nuclear reactor — either a fusion or fission reactor — can also produce tritium, and helium-3 after decay.
Due to the lower atomic mass of helium-3 (3.0160293 amu), it 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 lower mass of helium-3 causes 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 compared to helium-4's 4.23 K, and its critical point 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.
|First Generation Fusion Fuels|
|21H + 21H (D-D)||→||32He + 10n||3.268 MeV||.306|
|21H + 21H (D-D)||→||31H + 11p||4.032 MeV||0|
|21H + 31H (D-T)||→||42He + 10n||17.571 MeV||.057|
|Second Generation Fusion Fuel|
|21H + 32He (D-3He)||→||42He + 11p||18.354 MeV||0|
|Third Generation Fusion Fuels|
|32He + 32He||→||42He+ 211p||12.86 MeV||0|
|115B + 11p||→||3 42He||8.68 MeV||0|
|Net result of D burning (sum of first 4 rows)|
|6D||→||2(4He + n + p)||43.225 MeV||.046|
|Current nuclear fuel|
|235U + n||→||2 FP+ 2.5n||~200 MeV||.001|
Some fusion processes produce highly energetic neutrons which render reactor components radioactive with activation products 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 nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the proton, 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.
Due to the higher Coulomb barrier, the temperatures required for 21H + 32He fusion are much higher than those of conventional 2H + 31H (deuterium + tritium) 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 + 21H) does produce a neutron. 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 possiblity, 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 amounts of helium-3 needed as a replacement for conventional fuels are substantial by comparison to amounts currently available. The total amount of energy produced in the 21H + 32He reaction is 18.4 MeV, which corresponds to some 493 megawatt-hours (4.93x108 W·h) per three grams (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 thousand-megawatt 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" (1.14x1015 W·h). Again assuming 100% conversion efficiency, 6.7 tons of helium-3 would be required just for that segment of one country's energy demand, 15 to 20 tons given a more realistic end-to-end conversion efficiency.
Helium-3 is a most important isotope in instrumentation for neutron detection. It has a high absorption cross section for thermal neutron 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
Furthermore, the absorption process is strongly spin-dependent, which allows a spin-polarized 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 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 has to some extent prevented this.
A helium-3 refrigerator uses helium-3 to achieve temperatures of 0.2 to 0.3 kelvin. A dilution refrigerator uses a mixture of helium-3 and helium-4 to reach cryogenic temperatures as low as a few thousandths of a kelvin.
An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a fermion since it contains an odd number of spin 1/2 particles. Helium-4 nuclei are bosons, 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: A fraction of it enters a superfluid phase 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 pairs in the BCS theory of superconductivity. Each Cooper pair, having integer spin, can be thought of as a boson. During the 1970s, David Lee, Douglas Osheroff and Robert Coleman Richardson 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 on the melting curve. They were awarded the 1996 Nobel Prize in Physics for their discovery. Tony Leggett 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.
Due to the rarity of helium-3 on Earth, it is manufactured instead of recovered from natural deposits. Helium-3 is a byproduct of tritium decay, and tritium can be produced through neutron bombardment of lithium, boron, or nitrogen targets. Current supplies of helium-3 come, in part, from the dismantling of nuclear weapons where it accumulates; approximately 150 kilograms of it have resulted from decay of US tritium production since 1955, most of which was for warheads. However, the production and storage of huge amounts of the gas tritium is probably uneconomical, as tritium must be produced at the same rate as helium-3, and roughly eighteen times as much of tritium stock is required 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). If commercial fusion reactors were to use helium-3 as a fuel, they would require tens of tons of helium-3 each year to produce a fraction of the world's power, implying need for the same amount of new tritium production, as well as the need to keep 18 times this figure in total tritium breeder stocks. 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. Note that any breeding of tritium on Earth requires the use of a high neutron flux, which proponents of helium-3 nuclear reactors hope to avoid.
Solar nebula (primordial) abundanceEdit
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.
- Main article: isotope geochemistry
3He is a primordial substance in the Earth's mantle, 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 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 from Edison Mine, South Dakota were found to contain 12 parts of He-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 percent (above 0.2 percent 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 He-3.
3He is also present in the Earth's atmosphere. The natural abundance of 3He in naturally occurring helium gas is 1.38×10-6 (1.38 parts per million). The partial pressure of helium in the Earth's atmosphere is about 4 millitorr, and thus helium accounts for 5.2 parts per million of the total pressure (760 torr) 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 x 1015metric tons, the mass of 3He in the Earth's atmosphere is the product of these numbers, or 37,000 tons of 3He.
3He is produced on Earth from three sources: lithium spallation, 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 emissions.
Template:RelevanceThe total amount of helium-3 in the mantle may be in the range of 100 thousand to a million tonnes. However, this mantle helium is not directly accessible.Template:Clarify me Some of it leaks up through deep-sourced hotspot volcanoes such as those of the Hawaiian islands, but only 300 grams per year is emitted to the atmosphere. Mid-ocean ridges emit another 3 kilogram per year. Around subduction zones, various sources produce helium-3 in natural gas 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.Template:Clarify me
Medical lung imagingEdit
The nuclei of some atoms (such as He-3, but not He-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 helium-3 gas may be produced directly with lasers of the appropriate frequency. With the use of a thin layer of protective cesium 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.
The Moon's surface contains helium-3 at concentrations on the order of 0.01 ppm. A number of people, starting with Gerald Kulcinski in 1986, have proposed to explore the moon, mine lunar regolith and use the helium-3 for fusion. Because of the low concentrations of helium-3, any mining equipment would need to process extremely large amounts of regolith (over 100 million tons 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 and geochemist Ouyang Ziyuan from the Chinese Academy of Sciences who is now in charge of the Chinese Lunar Exploration Program 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 of current spacecraft 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 tons of regolith) per week would be necessary.
Mining gas giants for helium-3 has also been proposed. The British Interplanetary Society's hypothetical Project Daedalus interstellar probe design was fueled by helium-3 mines in the atmosphere of Jupiter, 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.
A second-generation approach to controlled fusion power involves combining helium-3 (32He) and deuterium (21H). This reaction produces a helium-4 ion (42He) (like an alpha particle, but of different origin) and a high-energy proton (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 ions and the fusion protons. Protons, as positively charged particles, can be converted directly into electricity, through use of solid-state conversion materials as well as other techniques. Potential conversion efficiencies of 70 percent may be possible, as there is no need to convert proton energy to heat in order to drive a turbine-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 and helium-3 would offer lower capital and operating costs than their competitors due to less technical complexity, higher conversion efficiency, smaller size, the absence of radioactive fuel, no air or water pollution, and only low-level radioactive waste disposal requirements. Recent estimates suggest that about $6 billion in investment capital will be required to develop and construct the first helium-3 fusion power plant. Financial breakeven at today's wholesale electricity 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 (such as National Ignition Facility) and magnetic confinement fusion (such as ITER and other tokamaks). 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 for this reaction; for D+He-3, the barrier is much higher, and He-3–He-3 higher still. The immense cost of reactors like ITER and National Ignition Facility 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–He-3 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 He-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–He-3 fusion, a number of other reactors have been proposed – the Fusor, Polywell, 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" fuels. However, these systems would scale well enough that their proponents tend to promote p-B fusion, which requires no exotic fuels like He-3.
Notes and referencesEdit
- ↑ Slyuta, E. N.; Abdrakhimov, A. M.; Galimov, E. M. (March 12-16, 2007). "The Estimation of Helium-3 Probable Reserves in Lunar Regolith" in 38th Lunar and Planetary Science Conference.: 2175. }
- ↑ Oliphant, M. L. E.; Harteck, P.; Rutherford, E. (1934). "Transmutation Effects Observed with Heavy Hydrogen". Proceedings of the Royal Society of London. A 144 (853): 692–703. doi:10.1098/rspa.1934.0077, http://www.jstor.org/stable/2935553.
- ↑ "Lawrence and His Laboratory: Episode: A Productive Error". Newsmagazine Publication (1981). Retrieved on 2009-09-01.
- ↑ Teragon's Summary of Cryogen Properties Teragon Research, 2005
- ↑ Huang Y.H., Chen G.B., Li X.Y. Arp V.D. Density equation for saturated 3He. Int. J. Thermophys., 2005, 26:1-13.
- ↑ Huang Y.H., Chen G.B. A practical vapor pressure equation for helium-3 from 0.01 K to the critical point. Cryogenics, 2006, 46(12): 833-839.
- ↑ Huang Y.H., Chen G.B. Melting-pressure and density equations of 3He at temperatures from 0.001 to 30 K. Phys. Rev. B, 2005, 72(18):184513.
- ↑ Huang Y.H., Chen G.B., and Arp V.D. Debye equation of state for fluid helium-3, J. Chem. Phys., 2006, 125: 1-10.
- ↑ "Inertial Electrostatic Confinement Fusion". Retrieved on 2007-05-06.
- ↑ "Nuclear Fission and Fusion". Retrieved on 2007-05-06.
- ↑ "The Fusion Reaction". Retrieved on 2007-05-06.
- ↑ John Santarius (June 2006). "A Strategy for D - 3He Development" (PDF). Retrieved on 2007-05-06.
- ↑ "Nuclear Reactions". Retrieved on 2007-05-06.
- ↑ John Santarius (September 28, 2004). "Lunar 3He and Fusion Power" (PDF). Retrieved on 2007-05-06.
- ↑ A Modular Neutron Detector | Summer 2003| Los Alamos National Laboratory
- ↑ NCNR Neutron Spin Filters
- ↑ Polarization Analysis using Polarized 3He
- ↑ Nuclear Bomb Detectors Stopped by Material Shortage
- ↑ Dilution Refrigeration
- ↑ Osheroff, D. D.; Richardson, R. C.; Lee, D. M. (1972). "Evidence for a New Phase of Solid He3". Physical Review Letters 28 (14): 885–888. doi:10.1103/PhysRevLett.28.885.
- ↑ Osheroff, D. D.; Gully, W. J.; Richardson, R. C.; Lee, D. M. (1972). "New Magnetic Phenomena in Liquid He3 below 3 mK". Physical Review Letters 29 (14): 920–923. doi:10.1103/PhysRevLett.29.920.
- ↑ Leggett, A. J. (1972). "Interpretation of Recent Results on He3 below 3 mK: A New Liquid Phase?". Physical Review Letters 29 (18): 1227–1230. doi:10.1103/PhysRevLett.29.1227.
- ↑ http://afci.lanl.gov/aptnews/aptnews.mar1_98.html
- ↑ IEER: Science for Democratic Action Vol. 5 No. 1
- ↑ 25.0 25.1 Wittenberg 1994
- ↑ http://adsabs.harvard.edu/abs/1996Sci...272..846N
- ↑ 27.0 27.1 Aldrich, L.T.; Nier, Alfred O. Phys. Rev. 74, 1590 - 1594 (1948). The Occurrence of He3 in Natural Sources of Helium. Page 1592, Tables I and II.
- ↑ Holden, Normen E. 1993. Helium Isotopic Abundance Variation in Nature. copy of paper BNL-49331 "Table II. 3He Abundance of Natural Gas ... 3He in ppm ... Aldrich 0.05 - 0.5 ... Sano 0.46 - 22.7", "Table V. ... of Water ... 3He in ppm ... 1.6 - 1.8 East Pacific ... 0.006 - 1.5 Manitoba Chalk River ... 164 Japan Sea" (Aldrich measured Helium from US wells, Sano that of Taiwan gas )
- ↑ WebElements Periodic Table: Professional Edition: Helium: key information
- ↑ 30.0 30.1 30.2 Smith, D.M. "any concentration of helium above approximately 0.2 percent is considered worthwhile examining" ... "U.S. government still owns approximately 1 billion nm3 of helium inventory", "Middle East and North Africa ... many very large, helium-rich (up to 0.5 percent) natural gas fields" (Smith uses nm3 to mean "normal cubic metre", elsewhere called "cubic metre at STP)
- ↑ The Mass of the Atmosphere: A Constraint on Global Analyses
- ↑ Wittenberg 1994 Page 3, Table 1. Page 9.
- ↑ Wittenberg 1994 Page A-1 citing Anderson 1993, "1200 metric tone"
- ↑ Wittenberg 1994 Page A-4 "1 kg (3He), pumping power would be 1.13x10^6MYyr ... fusion power derived ... 19 MWyr"
- ↑ Wittenberg 1994 Page A-4 using Table 1 page A-5 of US crustal natural gas
- ↑ Take a deep breath of nuclear spin - CERN Courier
- ↑ FTI Research Projects :: 3He Lunar Mining
- ↑ E. N. Slyuta and A. M. Abdrakhimov, and E. M. Galimov (2007). "The estimation of helium-3 probable reserves in lunar regolith" (PDF). Lunar and Planetary Science XXXVIII.
- ↑ Eric R. Hedman (January 16, 2006). "A fascinating hour with Gerald Kulcinski", The Space Review.
- ↑ I.N. Sviatoslavsky (November 1993). "The challenge of mining He-3 on the lunar surface: how all the parts fit together" (PDF). Wisconsin Center for Space Automation and Robotics Technical Report WCSAR-TR-AR3-9311-2.
- ↑ "With He-3 on mind, India gets ready for lunar mission".
- ↑ http://www.isro.org/chandrayaan/htmls/objective_scientific.htm
- ↑ http://luna-ci.blogspot.com/2008/11/chandrayaan-1-payload-feature-2-sub-kev.html
- ↑ He asked for the moon-and got it
- ↑ SPACE.com - Russian Rocket Builder Aims for Moon Base by 2015, Reports Say
- ↑ James Oberg (February 6, 2006). "Moonscam: Russians try to sell the Moon for foreign cash".
- ↑ Dwayne A. Day (March 5, 2007). "Death throes and grand delusions". The Space Review.
- ↑ Bryan Palaszewski. "Atmospheric Mining in the Outer Solar System" (PDF). NASA Technical Memorandum 2006-214122. AIAA–2005–4319. Prepared for the 41st Joint Propulsion Conference and Exhibit cosponsored by AIAA, ASME, SAE, and ASEE, Tucson, Arizona, July 10–13, 2005.
- ↑ Paul DiMare (October 2004). "Mining The Moon". Retrieved on 6 May 2007.
- ↑ "ITER & Beyond". Retrieved on 4 August 2009.
- ↑ Todd Rider (accessdate = 2007-05-07). "A general critique of inertial-electrostatic confinement fusion systems".
- D.M Smith, T.W. Goodwin, J.A.Schiller. "Challenges to the worldwide supply of helium in the next decade" (pdf). Air Products and Chemicals, Inc. Retrieved on 2008-07-01.
- L.J. Wittenberg (July 1994). "Non-Lunar 3He Resources" (pdf). Retrieved on 2008-07-01.
- The Nobel Prize in Physics 2003, presentation speech
- Moon for Sale: A BBC Horizon Documentary on the possibility of Lunar mining for Helium-3
- More background information about Helium 3