:"This article is about the elemental isotope. For the record label Helium 3, see Muse or
A&E Records".infobox isotope
background = #F99
isotope_name = Helium-3
beta decayof tritium
Helium-3 (He-3) is a light, non-
radioactive isotopeof heliumwith two protons and one neutron, rare on Earth, sought for use in nuclear fusionresearch. The abundance of helium-3 is thought to be greater on the Moon(embedded in the upper layer of regolithby the solar windover 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). [http://www.moonminer.com/Lunar_regolith.html, [http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf The estimation of helium-3 probable reserves in lunar regolith] ] It is proposed to be used as a second-generation fusion power source.
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 Oliphantwhile 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 Cornogin a cyclotron experiment at the Lawrence Berkeley National Laboratory, in 1939. [ [http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1981/81fepi1.html Lawrence and His Laboratory: Episode: A Productive Error ] ]
Helium-3's atomic mass of 3.0160293, being significantly lower than Helium-4's 4.0026, causes it to have significantly different properties. Helium-3 boils at 3.19
kelvins 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. [ [http://www.trgn.com/database/cryogen.html Teragon's Summary of Cryogen Properties] Teragon Research, 2005]
Some fusion processes produce highly energetic neutrons which render reactor components
radioactivethrough the continuous bombardment of the reactor's components with the said same neutrons. Because of this bombardment and irradiation, power generationmust occur indirectly through thermal means, as in a fission reactor. However, the appeal of helium-3 fusion stems from the nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the protoncan 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. [ cite web | url = http://fti.neep.wisc.edu/presentations/jfs_ieee0904.pdf | title = Lunar 3He and Fusion Power | author = John Santarius | date = September 28, 2004| accessdate = 2007-05-06 ]
However, since both reactants need to be mixed together to fuse, side reactions (21H + 21H and 32He+ 32He) will occur, the first of which is not aneutronic. Therefore in practice this reaction is unlikely to ever be completely 'clean', thus negating some of its attraction. Also, 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.
The amounts of helium-3 needed as a replacement for conventional fuels should not be underestimated. The total amount of energy produced in the 21H + 32He reaction is 18.4 MeV, which corresponds to some 493 megawatt-hours (4.93x108 Wh) 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 kWh" (1.114x1015 Wh). 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 tonnes given a more realistic end-to-end conversion efficiency. Fact|date=May 2007
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 MeVinto charged particles tritium(T, 3H) and proton(p, 1H) which then are detected by creating a charge cloud in the stopping gas of a proportional counteror a Geiger-Müller tube. [ [http://www.lanl.gov/quarterly/q_sum03/neutron_detect.shtml A Modular Neutron Detector | Summer 2003| Los Alamos National Laboratory ] ]
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. [ [http://www.ncnr.nist.gov/AnnualReport/FY2002_html/pages/neutron_spin.htm NCNR Neutron Spin Filters ] ] [ [http://physics.nist.gov/Divisions/Div846/Gp3/Helium/applications/neutronApps/PolarAnalysis.html Polarization Analysis using Polarized 3He ] ]
helium-3 refrigeratoruses helium-3 to achieve temperatures of 0.2 to 0.3 kelvin. A dilution refrigeratoruses a mixture of helium-3 and helium-4 to reach cryogenic temperatures as low as a few thousandths of a kelvin. [ [http://na47sun05.cern.ch/target/outline/dilref.html Dilution Refrigeration ] ]
An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a
fermionsince 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 superfluidphase 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 theoryof superconductivity. Each Cooper pair, having integer spin, can be thought of as a boson. During the 1970s, David Morris Lee, Douglas Osheroffand Robert Coleman Richardsondiscovered two phase transitions along the melting curve, which was soon realized to be the two superfluid phases of helium-3. [cite journal |last=Osheroff |first=D. D. |authorlink= |coauthors=Richardson, R. C.; Lee, D. M. |year=1972 |month= |title=Evidence for a New Phase of Solid He3 |journal= Physical Review Letters|volume=28 |issue=14 |pages=885–888 |doi=10.1103/PhysRevLett.28.885 |url= |accessdate= |quote= ] [cite journal |last=Osheroff |first=D. D. |authorlink= |coauthors=Gully, W. J.; Richardson, R. C.; Lee, D. M. |year=1972 |month= |title=New Magnetic Phenomena in Liquid He3 below 3 mK |journal=Physical Review Letters |volume=29 |issue=14 |pages=920–923 |doi=10.1103/PhysRevLett.29.920 |url= |accessdate= |quote= ] The transition to a superfluid occurs at 2.491 millikelvins on the melting curve. They were awarded the 1996 Nobel Prize in Physicsfor their discovery. Tony Leggett won the 2003Nobel Prize in Physics for his work on refining understanding of the superfluid phase of helium-3. [cite journal |last=Leggett |first=A. J. |authorlink= |coauthors= |year=1972 |month= |title=Interpretation of Recent Results on He3 below 3 mK: A New Liquid Phase? |journal=Physical Review Letters |volume=29 |issue=18 |pages=1227–1230 |doi=10.1103/PhysRevLett.29.1227 |url= |accessdate= |quote= ]
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 typically manufactured instead of recovered from natural deposits. Helium-3 is a byproduct of
tritiumdecay, and tritium can be produced through neutron bombardment of lithium, boron, or nitrogentargets. Current supplies of helium-3 come, in part, from the dismantling of nuclear weapons where it accumulates [http://afci.lanl.gov/aptnews/aptnews.mar1_98.html] ; approximately 150 kilograms of it have resulted from decay of US tritium production since 1955, most of which was for warheads [ [http://www.ieer.org/sdafiles/vol_5/5-1/tritium.html IEER: Science for Democratic Action Vol. 5 No. 1 ] ] . However, the production and storage of huge amounts of the gas tritium is probably uneconomical, as roughly eighteen tons of tritium stock are required for each ton 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 * [ln2/t½] where the value of t½/(ln2) 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.Wittenberg 1994] 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. Fact|date=May 2007
Medical lung imaging
Polarized helium-3 may be produced directly with lasers of the appropriate power, and with a thin layer of protective Cs metal on the inside of cylinders, the magnetized gas may 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 [ [http://www.cerncourier.com/main/article/41/8/14 Take a deep breath of nuclear spin - CERN Courier ] ] .
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.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. [http://www.osti.gov/bridge/servlets/purl/10183304-ds0WIi/10183304.PDF 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 [http://www.nature.com/nature/journal/v323/n6083/abs/323055a0.html] )] Samples of the ore
Spodumenefrom 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, [ [http://www.webelements.com/webelements/elements/text/He/key.html WebElements Periodic Table: Professional Edition: Helium: key information] ] and large sources have over 0.5 percent (above 0.2 percent makes it viable to extract).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" (nm is "
Normal cubic metre")] Algeria's annual gas production is assumed to contain 100 million Nm3 and this would contain between 5 and 50 Nm3 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 Nm3 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 1.38e|-6. The partial pressure of helium in the Earth's atmosphere is about 4 millitorr, and thus 5.2 parts per millionclarifyme|date=July 2008 of helium. It has been proven that the Earth's atmosphere contains approximately 4000 tons of 3He.Fact|date=July 2008
3He is produced on Earth from three sources: lithium
spallation, cosmic rays, and 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 particleemissions.
Moon's surface contains helium-3 at concentrations on the order of 0.01 ppm. [ [http://fti.neep.wisc.edu/Research/he3_pubs.html FTI Research Projects :: 3He Lunar Mining ] ] [cite web | url= http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf | title = The estimation of helium-3 probable reserves in lunar regolith | author = E. N. Slyuta and A. M. Abdrakhimov, and E. M. Galimov | work = Lunar and Planetary Science XXXVIII | year=2007] A number of people, starting with Gerald Kulcinskiin 1986, [cite news | url = http://www.thespacereview.com/article/536/1 | title = A fascinating hour with Gerald Kulcinski| author=Eric R. Hedman | date = January 16, 2006 | work = The Space Review] have proposed to explore the moon, mine lunar regolithand using the helium-3 for fusion. Because of the low concentrations of helium-3, any mining equipment would need to process large amounts of regolith, [cite web | title = The challenge of mining He-3 on the lunar surface: how all the parts fit together | author = I.N. Sviatoslavsky | date = November 1993 | url = http://fti.neep.wisc.edu/pdf/wcsar9311-2.pdf Wisconsin Center for Space Automation and Robotics Technical Report WCSAR-TR-AR3-9311-2.] and some proposals have suggested that helium-3 extraction be piggybacked onto a larger mining and development operation.Fact|date=August 2007
geochemist Ouyang Ziyuanfrom the Chinese Academy of Scienceswho 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." [ [http://www.chinadaily.com.cn/cndy/2006-07/26/content_649325.htm He asked for the moon-and got it ] ]
In January 2006 the Russian space company
RKK Energiyaannounced that it considers lunar helium-3 a potential economic resource to be mined by 2020, [ [http://www.space.com/news/ap_060126_russia_moon.html SPACE.com - Russian Rocket Builder Aims for Moon Base by 2015, Reports Say ] ] if funding can be found. [cite web | url = http://www.thespacereview.com/article/551/1 | title = Moonscam: Russians try to sell the Moon for foreign cash | author = James Oberg | date = February 6, 2006] [cite web | url = http://www.thespacereview.com/article/824/1 | title = Death throes and grand delusions | author = Dwayne A. Day| work = The Space Review| date=March 5, 2007]
Indian Space Research Organization (ISRO) plans to send a lunar probe mission called Chandrayan-I tentatively scheduled to be launched between Oct 19 and 28 2008. Its mission includes mapping the lunar surface for the helium-3 (He-3) mineral to fuel nuclear power plants. [ cite web | url = http://economictimes.indiatimes.com/News/News_By_Industry/ET_Cetera/With_He-3_on_mind_India_gets_ready_for_lunar_mission/articleshow/3500270.cms | title = With He-3 on mind, India gets ready for lunar mission ]
gas giants for helium-3 has also been proposed. [cite web | title = Atmospheric Mining in the Outer Solar System | author = Bryan Palaszewski | url = http://gltrs.grc.nasa.gov/reports/2006/TM-2006-214122.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.] The British Interplanetary Society's hypothetical Project Daedalusinterstellar probe design was fueled by helium-3 mines on the planet 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 an helium-4ion (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 electrostaticfields to control fuel ions and the fusion protons. Protons, as positively charged particles, can be converted directly into electricity, through use of solid-stateconversion 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 turbine-powered generators.
There have been many claims about the capabilities of Helium-3 power plants. According to proponents, fusion power plants operating on
deuteriumand 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 radioactivewaste disposal requirements. Recent estimates suggest that about $6 billion in investmentcapital will be required to develop and construct the first helium-3 fusion power plant. Financial breakeven at today's wholesale electricityprices (5 US cents per kilowatt-hour) would occur after five 1000- megawattplants were on line, replacing old conventional plants or meeting new demand. [ cite news | url = http://www.popularmechanics.com/science/air_space/1283056.html?page=4 | title = Mining The Moon | author = Paul DiMare | date = October 2004| accessdate = 2007-05-06 ]
The reality is not so clean-cut. The most advanced fusion programs in the world are
inertial confinement fusion(such as National Ignition Facility) and magnetic confinement fusion(such as ITERand 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[cite news | url = http://www.iter.org/Future-beyond.htm | title = Beyond ITER | accessdate = 2007-05-07] . In both cases, the type of fusion discussed is the simplest: D-T fusion. The reason for this is the very low Coulomb barrierfor this reaction; for D+He-3, the barrier is much higher, and He-3–He-3 higher still. The immense cost of reactors like ITERand National Ignition Facilityare 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. These generally attempt to achieve fusion in thermal disequilibrium, something that could potentially prove impossible [cite news | url = http://dspace.mit.edu/handle/1721.1/29869 | title = A general critique of inertial-electrostatic confinement fusion systems | author = Todd Rider | date = accessdate = 2007-05-07] , 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 references
* cite paper
author=D.M Smith, T.W. Goodwin, J.A.Schiller
title=CHALLENGES TO THE WORLDWIDE SUPPLY OF HELIUM IN THE NEXT DECADE
publisher=Air Products and Chemicals, Inc
* cite paper
title=Non-Lunar 3He Resources
* [http://nobelprize.org/physics/laureates/2003/presentation-speech.html The Nobel Prize in Physics 2003, presentation speech]
* [http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/moonsale/ Moon for Sale: A BBC Horizon Documentary on the possibility of Lunar mining for Helium-3]
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