Wikipedia - Benutzerbeiträge [de]

Beta Comae Berenices

2009-11-25T16:46:15Z

Ataleh: interwiki

{{Starbox begin |
name=Beta Comae Bernices }}
{{Starbox observe |
epoch=J2000 |
ra=13h 11 m 52.4s |
dec=+27° 52' 41" |
appmag_v=4.26 |
constell=[[Coma Berenices]] }}
{{Starbox character |
class=G0V |
b-v=0.57 |
u-b=0.07 |
variable=None }}
{{Starbox astrometry |
radial_v=+5.2 |
prop_mo_ra=-801.94 |
prop_mo_dec=882.70 |
parallax=108.87 |
p_error=0.69 |
absmag_v=4.45 }}
{{Starbox detail|
age=1.7-4.4 {{E|9}} |
metal=146% |
mass=1.05 |
radius=1.19 |
rotation=~6 km/s. (~10 days) |
luminosity=1.42 |
temperature=6,000 }}
{{Starbox catalog |
names=43 Com, Beta Com, [[Henry L. Giclas catalogue|Gl]] 502, [[Gliese-Jahreiss catalogue|GJ]] 876, [[Henry Draper catalogue|HD]] 114710, [[Harvard Revised catalogue|HR]] 4983, [[Bonner Durchmusterung|BD]] +28°2193, [[General Catalogue of Trigonometric Parallaxes|GCTP]] 3015.00, [[Luyten Half-Second catalogue|LHS]] 348, [[Luyten Five-Tenths catalogue|LFT]] 978, [[Luyten Two-Tenths catalogue|LTT]] 13815, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 82706, FK5 492, [[Hipparcos catalogue|HIP]] 64394. }}
{{Starbox end}}

'''Beta Coma Berenices''' (β Comae Berenices / β Com) is a [[main sequence]] dwarf [[star]] in the [[constellation]] of [[Coma Berenices]]. The [[Greek letter]] [[Beta (letter)|beta]] (β) usually indicates that the star has the second highest [[apparent magnitude|visual magnitude]] in the constellation. In actuality, however, it is slightly brighter than [[Alpha Comae Berenices|α Comae Berenices]].

This star is similar to our own [[Sun]], being only slightly larger and brighter in [[absolute magnitude]]. The surface of this star has a measured activity cycle of 16.6 years (compared to 11 years on our Sun.) It may also have a secondary activity cycle of 9.6 years. At one time it was thought that this star may have a [[spectroscopic binary|spectroscopic companion]]. However this was ruled out by means of more accurate radial velocity measurements. No [[planet]]s have yet been detected around this star, and there is no evidence of a [[circumstellar disk|dusty disk]].

==External links==
* [http://www.solstation.com/stars/beta-com.htm SolStation entry]

[[Category:Bayer objects|Comae Berenices, Beta]]
[[Category:Coma Berenices constellation]]
[[Category:G-type main sequence stars]]

[[es:Beta Comae Berenices]]
[[fr:Beta Comae Berenices]]
[[ko:머리털자리 베타]]
[[it:Beta Comae Berenices]]
[[ja:かみのけ座ベータ星]]
[[pl:Beta Comae Berenices]]
[[ru:Бета Волос Вероники]]
[[sk:Beta Comae Berenices]]
[[fi:Beta Comae Berenices]]

42 Draconis

2009-08-25T20:32:26Z

Ataleh: Template added

{{Starbox begin
| name = [[Flamsteed designation|42]] Draconis b
}}
{{Starbox observe
| epoch = [[J2000.0]]
| constell = [[Draco (constellation)|Draco]]
| ra = {{RA|18|25|59.1381}}
| dec = {{DEC|+65|33|48.530}}
| appmag_v = 4.833
}}
{{Starbox character
| spectral = K1.5III
| r-i =
| v-r =
| b-v = 1.187
| u-b =
| variable =
}}
{{Starbox astrometry
| radial_v = 32.17 ± 0.20
| prop_mo_ra = 106.52
| prop_mo_dec = –27.07
| parallax = 10.28
| p_error = 0.48
| absmag_v = –0.108
}}
{{Starbox detail
| mass = 0.98 ± 0.05
| radius = 22.03 ± 1
| gravity = 0.929
| luminosity = 135
| temperature = 4200 ± 70
| metal = 35% Sun
| age = 9.49 billion
| rotation =
}}
{{Starbox catalog
| names = [[Durchmusterung|BD]]+65°1271, [[Boss General Catalogue|GC]] 25212, [[General Catalogue of Variable Stars|GCRV]] 10941, [[Henry Draper catalogue|HD]] 170693, [[Hipparcos catalogue|HIP]] 90344, [[Harvard Revised catalogue|HR]] 6945, [[PPM star catalogue|PPM]] 20916, [[Smithsonian Astrophysical Observatory catalogue|SAO]] 17888
}}
{{Starbox reference
| Simbad = 42+Dra
| EPE = 42+Dra
}}
{{Starbox end}}

'''42 Draconis''' is a 5th [[apparent magnitude|magnitude]] [[K-type star|K-type]] [[giant star|giant]] [[star]] located approximately 317 [[light year]]s away in the [[constellation]] of [[Draco (constellation)|Draco]]. The star has mass similar to our Sun but its radius is 22 times greater. It is a metal-poor star with metallicity as low as 35% that of our Sun and its age is 9.49 billion years. In 2009, this star was found to have a [[super-Jupiter]] in orbit around it.

{{OrbitboxPlanet begin}}
{{OrbitboxPlanet
| exoplanet = [[42 Draconis b|b]]
| mass = >3.88 ± 0.85
| period = 479.1 ± 6.2
| semimajor = 1.19 ± 0.01
| eccentricity = 0.38 ± 0.06
}}
{{Orbitbox end}}

== See also ==
* [[HD 139357]]
* [[Iota Draconis]]
* [[List of extrasolar planets]]
* [[List of stars in Draco]]

== References ==
* {{cite journal | title=Planetary companion candidates around the K giant stars 42 Draconis and HD 139357 | journal=Astronomy & Astrophysics | year=2009 | volume= | issue= | pages= | last1=Doellinger | first1=M. P. | last2=Hatzes | first2=A. P. | last3=Pasquini | first3=L. | last4=Guenther | first4=E. W. | last5=Hartmann | first5=M. | last6=Girardi | first6=L. | id={{arXiv|0903.3593}}}}
{{Sky|18|25|59.1381|+|65|33|48.530|317.4}}
[[Category:K-type giants]]
[[Category:Flamsteed objects|Draconis, 42]]
[[Category:HD and HDE objects|170693]]
[[Category:HIP objects|090344]]
[[Category:HR objects|6945]]
[[Category:Draco constellation]]
[[Category:Planetary systems]]

{{Stars of Draco}}

{{giant-star-stub}}
{{exoplanet-stub}}

[[es:42 Draconis]]
[[ko:용자리 42]]

Pekuliärer Stern

2009-08-10T14:48:55Z

Ataleh: Template added

In astrophysics, '''peculiar stars''' have distinctly unusual metal abundances, at least in their surface layers.

Chemically peculiar stars (CP stars) are common among hot [[main sequence]] (hydrogen-burning) stars. These hot peculiar stars have been divided into 4 main classes on the basis of their spectra, although two classification systems are sometimes used<ref>Preston, George. Annual Review of Astronomy and Astrophysics, vol 12, p 257, 1974[http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.aa.12.090174.001353]</ref>: [[metallic-lined star|metallic-lined]] (Am, CP1), [[Ap star|Ap]] (CP2), [[mercury-manganese star|mercury-manganese]] (HgMn, CP3) and helium-weak (He-weak, CP4). The class names give a good idea of what peculiarities sets them apart and have been.

The Am stars (CP1 stars) show weak lines of singly ionized Ca and/or Sc, but show enhanced abundances of heavy metals. They also tend to be slow rotators and have an [[effective temperature]] between 7000 K and 10 000 K. The Ap stars (CP2 stars) are characterized by strong magnetic fields, enhanced abundances of elements such as Si, Cr, Sr and Eu and are also generally slow rotators. The [[effective temperature]] of these stars is stated to be between 8000 K and 15 000 K, but the issue of calculating effective temperatures in such peculiar stars is complicated by atmospheric structure. The HgMn stars (CP3 stars) are also classically placed within the Ap category, but do not show the strong magnetic fields associated with classical Ap stars. As the name implies, these stars show increased abundances of singly ionized Hg and Mn. These stars are also very slow rotators, even by the standards of CP stars. The [[effective temperature]] range for these stars is quoted at between 10 000 K and 15 000 K. The He-weak stars (CP4 stars) show weaker He lines than would be expected classically from their observed Johnson ''UBV'' colours.

It is generally thought that the peculiar surface compositions observed in these hot main-sequence stars have been caused by processes that happened after the star formed, such as diffusion or magnetic effects in the outer layers of the stars<ref>Michaud, G. Astrophysical Journal, vol 160, p 641, 1970[http://adsabs.harvard.edu/full/1970ApJ...160..641M]</ref>. These processes cause some elements to "settle", particularly He, N and O, out in the atmosphere into the layers below, while other elements, such as Mn, Sr, Y, Zr, are "levitated" out of the interior to the surface, resulting in the observed spectral peculiarities. It is assumed that the centers of the stars, and the bulk compositions of the entire star, have more normal chemical abundance mixtures which reflect the compositions of the gas clouds from which they formed.<ref>Preston, George. Annual Review of Astronomy and Astrophysics, vol 12, p 257, 1974[http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.aa.12.090174.001353]</ref> In order for such diffusion and levitation to occur and the resulting layers remain intact, the atmosphere of such a star must be stable enough to convection that convective mixing does not occur. The proposed mechanism causing this stability is the unusually large magnetic field that is generally observed in stars of this type.

There are also classes of chemically peculiar cool stars (that is, stars with [[spectral classification|spectral type]] G or later), but these stars are typically not main sequence stars. These are usually identified by the name of their class or some further specific label. The phrase ''chemically peculiar star'' without further specification usually means a member of one of the hot main sequence types described above.

Many of the cooler chemically peculiar stars are the result of the mixing of nuclear fusion products from the interior of the star to its surface; these include most of the [[carbon stars]] and [[S-type star]]s. Others are the result of [[mass transfer]] in a [[binary star]] system; examples of these include the [[Barium star|barium stars]] and some S stars.<ref>McClure, R. Journal of the Royal Astronomical Society of Canada, vol 79, pp. 277-293, Dec. 1985</ref>

== See also ==
*[[Przybylski’s star]]
*[[Normal star]]

== References ==

<references/>

{{Star}}

[[Category:Star types]]

[[es:Estrella peculiar]]
[[it:Stella peculiare]]
[[pt:Estrela peculiar]]
[[zh:特殊恆星]]

Bariumstern

2009-08-10T14:48:07Z

Ataleh: Template added

'''Barium stars''' are G to K class [[giant star|giants]], whose [[Star classification|spectra]] indicate an overabundance of [[s-process]] elements by the presence of singly ionized [[barium]], Ba II, at [[wavelength|λ]] 455.4nm. Barium stars also show enhanced spectral features of [[carbon]], the bands of the molecules CH, CN and C2. The class was originally recognized and defined by [[William Bidelman]] and [[Philip Keenan]].<ref>Bidelman, W.P., & Keenan, P.C. Astrophysical Journal, vol. 114, p. 473, 1951</ref>

Observational studies of their [[radial velocity]] suggested that all barium stars are [[binary stars]]<ref>McClure, R.D., Fletcher, J.M., & Nemec, J.M. Astrophysical Journal Letters, vol. 238, p. L35</ref><ref>McClure, R.D. & Woodsworth, A.W. Astrophysical Journal, vol. 352, pp. 709-723, April 1990.</ref><ref>Jorissen, A. & Mayor, M. Astronomy & Astrophysics, vol. 198, pp. 187-199, June 1988</ref> Observations in the [[ultraviolet]] using [[International Ultraviolet Explorer]] detected [[white dwarfs]] in some barium star systems.

Barium stars are believed to be the result of [[mass transfer]] in a [[binary star]] system. The mass transfer occurred when the presently-observed giant star was on the [[main sequence]]. Its companion, the donor star, was a [[carbon star]] on the [[asymptotic giant branch]] (AGB), and had produced carbon and s-process elements in its interior. These nuclear fusion products were mixed by [[convection]] to its surface. Some of that matter "polluted" the surface layers of the main sequence star as the donor star lost mass at the end of its AGB evolution, and it subsequently evolved to become a white dwarf. We are observing these systems an indeterminate amount of time after the mass transfer event, when the donor star has long been a white dwarf, and the "polluted" recipient star has evolved to become a [[red giant]].<ref>McClure, R. Journal of the Royals Astronomical Society of Canada, vol 79, pp. 277-293, Dec. 1985</ref>

During its evolution, the barium star will at times be larger and cooler than the limits of the spectral types G or K. When this happens, ordinarily such a star is spectral type M, but the s-process excesses may cause it to show its altered composition as another spectral peculiarity. While the star's surface temperature is in the M-type regime, the star may show molecular features of the s-process element [[zirconium]], zirconium oxide (ZrO) bands. When this happens, the star will appear as an "extrinsic" [[Stellar_classification#Class_S|S star]].

Historically, barium stars posed a puzzle, because in standard [[stellar evolution]] theory G and K giants are not far enough along in their evolution to have synthesized carbon and s-process elements and mix them to their surfaces. The discovery of the stars' binary nature resolved the puzzle, putting the source of their spectral peculiarities into a companion star which should have produced such material. The mass transfer episode is believed to be quite brief on an astronomical timescale. The mass transfer hypothesis predicts that there should be main sequence stars with barium star spectral peculiarities. At least one such star, HR 107, is known.<ref>Tomkin, J., Lambert, D.L., Edvardsson, B., Gustafsson, B., & Nissen, P.E., Astronomy & Astrophysics, vol 219, pp. L15-L18, July 1989</ref>

Prototypical barium stars include [[zeta Capricorni]], HR 774, and HR 4474.

The [[CH stars]] are [[Population II]] stars with similar evolutionary state, spectral peculiarities, and orbital statistics, and are believed to be the older, metal-poor analogs of the barium stars.<ref>McClure, R. Publications of the Astronomical Society of the Pacific, vol 96, p. 117, 1984</ref>

== References ==

<references/>

{{Star}}

[[Category:Star types]]

[[es:Estrella de bario]]
[[it:Stella al bario]]
[[hu:Báriumcsillag]]
[[fi:Bariumtähti]]
[[zh:鋇星]]

Später K-Hauptreihenstern

2009-08-10T14:41:09Z

Ataleh: Template added

{{star nav}}
A '''K V star''' is a [[main sequence]] ([[hydrogen]]-burning) [[star]] of [[spectral classification|spectral type]] K and luminosity class V. These stars are intermediate in size between red M-type main sequence stars of luminosity class V and yellow G-type main sequence stars of luminosity class V. They have masses of from 0.5 to 0.8 times the [[solar mass|mass]] of the [[Sun]] and [[effective temperature|surface temperature]]s between 3,900 and 5,200 [[Kelvin|K]].<ref name="hh">[http://adsabs.harvard.edu/abs/1981A&AS...46..193H Empirical bolometric corrections for the main-sequence], G. M. H. J. Habets and J. R. W. Heintze, ''Astronomy and Astrophysics Supplement'' '''46''' (November 1981), pp. 193–237.</ref>, Tables VII, VIII. Examples include [[Alpha Centauri B]] and [[Epsilon Indi]].<ref>[[SIMBAD]], entries for [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Alpha%20Centauri%20B Alpha Centauri B] and [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Epsilon%20Indi Epsilon Indi], accessed on line [[June 19]], [[2007]].</ref>

These stars are of particular interest in the search for extraterrestrial life because they are stable on the main sequence for a very long time (15 to 30 billion years, compared to 10 billion for the [[Sun]]). This may create an opportunity for life to evolve on terrestrial planets orbiting such stars.<ref> [http://www.newscientist.com/article/dn17084-orange-stars-are-just-right-for-life.html], retrieved on [[May 6]], [[2009]].</ref>

==References==
{{reflist}}

==See also==
* [[Solar twins]]
* [[Red dwarf]]

[[Category:Star types]]
[[Category:K-type main sequence stars| ]]

{{Star}}
{{main-star-stub}}

[[de:Oranger Zwerg]]
[[es:Enana naranja]]
[[fr:Naine orange]]
[[ko:K형 주계열성]]
[[id:Katai oranye]]
[[it:Nana arancione]]
[[mk:Портокалово џуџе]]
[[pl:Pomarańczowy karzeł]]
[[pt:Anã laranja]]
[[ru:Оранжевый карлик]]
[[sk:Oranžový trpaslík]]
[[zh:橙矮星]]

Helium-3

2009-04-10T11:09:58Z

Ataleh:

:''This article is about the elemental isotope. For the record label Helium 3, see [[Muse (band)|Muse]] or [[A&E Records]]''.
{{infobox isotope
| background = #F99
| isotope_name = Helium-3
| alternate_names =Helium-3, 3He, He-3
| symbol =He
| mass_number =3
| mass =3.0160293
| num_neutrons =1
| num_protons =2
| abundance =0.000137%
| halflife =stable
| error_halflife =
| text_color =
| image =
| parent =Tritium
| parent_symbol =H
| parent_mass =3
| parent_decay =[[beta decay]] of tritium
| spin =1/2+
}}
'''Helium-3''' (He-3) is a light, non-[[radioactive]] [[isotope]] of [[helium]] with two protons and one neutron, rare on [[Earth]], 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 giant]]s (left over from the original [[solar nebula]]), though still low in quantity (28 [[parts per million|ppm]] of lunar regolith is '''[[helium-4]]''' and 0.01 ppm is helium-3).<ref>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]</ref> It is proposed to be used as a second-generation fusion power source.

The [[helion (chemistry)|helion]], the [[atomic nucleus|nucleus]] of a helium-3 atom, consists of two [[proton]]s 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 [[University of Cambridge|Cambridge University]]'s [[Cavendish Laboratory]], in an experiment in which fast [[deuteron]]s 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 Walter Alvarez|Luis W. Alvarez]] and [[Robert Cornog]] in a cyclotron experiment at the [[Lawrence Berkeley National Laboratory]], in 1939. <ref>[http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1981/81fepi1.html Lawrence and His Laboratory: Episode: A Productive Error]</ref>

==Physical properties==
Helium-3's atomic mass of 3.0160293, being significantly lower than Helium-4's 4.0026, causes it to have significantly different properties since they are determined by induced dipole-dipole forces which are very mass dependent. Helium-3 boils at 3.19 [[kelvin]]s compared to helium-4's 4.23 K, and its [[critical point (thermodynamics)|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 [[Kilojoule per mole|kJ/mol]] compared to helium-4's 0.0829 kJ/mol.<ref>[http://www.trgn.com/database/cryogen.html Teragon's Summary of Cryogen Properties] Teragon Research, 2005</ref>

==Thermodynamic properties==
[[Equations of state]] for 3He are available along the vapor-liquid equilibrium line <ref>Huang Y.H., Chen G.B., Li X.Y. Arp V.D. Density equation for saturated 3He. Int. J. Thermophys., 2005, 26:1-13.</ref><ref>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. </ref>, the liquid-solid equilibrium line <ref>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.</ref> and the normal compressed liquid and gas phases <ref>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.</ref>.

==Fusion reactions==
{| class="wikitable" style="float:right;"
|+ Fusion reactions involving Helium-3<ref> {{cite web | url = http://members.tm.net/lapointe/IEC_Fusion.html | title = Inertial Electrostatic Confinement Fusion | accessdate = 2007-05-06 }} </ref><ref> {{cite web | url = http://www.lancs.ac.uk/ug/suttond1/#fusion | title = Nuclear Fission and Fusion | accessdate = 2007-05-06}} </ref><ref> {{cite web | url = http://library.thinkquest.org/28383/nowe_teksty/htmla/2_37a.html | title = The Fusion Reaction | accessdate = 2007-05-06}} </ref><ref> {{cite web | url = http://fti.neep.wisc.edu/pdf/fdm1291.pdf |format=PDF| title = A Strategy for D - 3He Development | author = John Santarius | month = June | year = 2006 | accessdate = 2007-05-06}} </ref><ref>{{cite web | url = http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucrea.html | title = Nuclear Reactions | accessdate = 2007-05-06}}</ref>
|-
! Reactants
!
! Products
! ''Q''
|-
! First Generation Fuels
|
|
|
|- style="text-align: center;"
| [[Deuterium|21H]] + [[Deuterium|21H]]
| →
| [[Helium-3|32He]] + 10n
| 3.268 [[MeV]]
|- style="text-align: center;"
| [[Deuterium|21H]] + [[Deuterium|21H]]
| →
| [[Tritium|31H]] + 11p
| 4.032 [[MeV]]
|- style="text-align: center;"
| [[Deuterium|21H]] + [[Tritium|31H]]
| →
| [[Helium-4|42He]] + 10n
| 17.571 [[MeV]]
|- style="text-align: center;"
! Second Generation Fuel
|
|
|
|- style="text-align: center;"
| [[Deuterium|21H]] + [[Helium-3|32He]]
| →
| [[Helium-4|42He]] + 11p
| 18.354 [[MeV]]
|- style="text-align: center;"
! Third Generation Fuel
|
|
|
|- style="text-align: center;"
| [[Helium-3|32He]] + [[Helium-3|32He]]
| →
| [[Helium-4|42He]]+ 211p
| 12.86 [[MeV]]
|}
Some fusion processes produce highly energetic neutrons which render reactor components [[radioactive]] 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 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.<ref> {{cite web | url = http://fti.neep.wisc.edu/presentations/jfs_ieee0904.pdf |format=PDF| title = Lunar 3He and Fusion Power | author = John Santarius | date = [[September 28]], [[2004]] | accessdate = 2007-05-06}} </ref>

However, since both reactants need to be mixed together to fuse, side reactions ([[Deuterium|21H]] + [[Deuterium|21H]] and [[Helium-3|32He]]+ [[Helium-3|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 [[Deuterium|21H]] + [[Helium-3|32He]] fusion are much higher than those of conventional [[Deuterium|2H]] + [[Tritium|31H]] ([[deuterium]] + [[tritium]]) fusion.

The amounts of helium-3 needed as a replacement for [[fossil fuel|conventional fuel]]s should not be underestimated. The total amount of energy produced in the [[Deuterium|21H]] + [[Helium-3|32He]] reaction is 18.4 M[[electronvolt|eV]], which corresponds to some 493 [[watt-hour|megawatt-hour]]s (4.93x108 Wh) per three [[gram]]s (one [[mole (chemistry)|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" (1.14x1015 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}}

==Neutron detection==
'''Helium-3''' is a most important isotope in instrumentation for [[neutron detection]]. It has a high absorption cross section for thermal [[neutron radiation|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
into 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 counter]] or a [[Geiger-Müller tube]]. <ref>[http://www.lanl.gov/quarterly/q_sum03/neutron_detect.shtml A Modular Neutron Detector | Summer 2003| Los Alamos National Laboratory]</ref>

Furthermore, the absorption process is strongly [[Spin (physics)|spin]]-dependent, which allows a [[Spin polarization|spin-polarized]] helium-3 volume to transmit neutrons with one spin component while absorbing the other. This effect is employed in [[Polarized neutron scattering|neutron polarization analysis]], a technique which probes for magnetic properties of matter.<ref>[http://www.ncnr.nist.gov/AnnualReport/FY2002_html/pages/neutron_spin.htm NCNR Neutron Spin Filters]</ref> <ref>[http://physics.nist.gov/Divisions/Div846/Gp3/Helium/applications/neutronApps/PolarAnalysis.html Polarization Analysis using Polarized 3He]</ref>

==Cryogenics==
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 [[cryogenics|cryogenic]] temperatures as low as a few thousandths of a [[kelvin]]. <ref>[http://na47sun05.cern.ch/target/outline/dilref.html Dilution Refrigeration]</ref>

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 [[boson]]s, containing an even number of spin 1/2 particles. This is a direct result of the [[Angular momentum quantum number#Addition of quantized angular momenta|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 (matter)|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 pair]]s in the [[BCS theory]] of [[superconductivity]]. Each Cooper pair, having integer spin, can be thought of as a boson. During the 1970s, [[David Morris Lee]], [[Douglas Osheroff]] and [[Robert Coleman Richardson]] discovered two phase transitions along the melting curve, which was soon realized to be the two superfluid phases of helium-3.<ref>{{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= }}</ref><ref>{{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= }}</ref> 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. [[Anthony James Leggett|Tony Leggett]] won the 2003 Nobel Prize in Physics for his work on refining understanding of the superfluid phase of helium-3.<ref>{{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= }}</ref>

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.

==Manufacturing==
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 [[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<ref>http://afci.lanl.gov/aptnews/aptnews.mar1_98.html</ref>; approximately 150 kilograms of it have resulted from decay of US tritium production since 1955, most of which was for warheads<ref>[http://www.ieer.org/sdafiles/vol_5/5-1/tritium.html IEER: Science for Democratic Action Vol. 5 No. 1]</ref>. 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 * [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, implying the same amount of tritium production, and 18 times this much total tritium stock.<ref name=Witt>[[#Witt|Wittenberg 1994]]</ref> 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}}

==Terrestrial occurrence==
{{main|isotope geochemistry}}
3He is a primordial substance in the Earth's [[mantle (geology)|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 [[helium-4|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.<ref name=Aldrich>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.</ref><ref name=Holden>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])</ref> 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.<ref name=Aldrich/>

Helium is also present as up to 7% of some natural gas sources,<ref>[http://www.webelements.com/webelements/elements/text/He/key.html WebElements Periodic Table: Professional Edition: Helium: key information]</ref> and large sources have over 0.5 percent (above 0.2 percent makes it viable to extract).<ref name=SmithDM>[[#Smith|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]]")</ref>Algeria's annual gas production is assumed to contain 100 million Nm3<ref name=SmithDM/> 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<ref name=SmithDM/> 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{{e|-6}}. The partial pressure of helium in the Earth's atmosphere is about 4 millitorr, and thus 5.2 parts per million{{Clarifyme|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 particle]] emissions.

{{relevance|date=July 2008}}The total amount of helium-3 in the mantle may be in the range of 100 thousand to a million [[tonne]]s. However, this mantle helium is not directly accessible.{{Clarifyme|date=July 2008}} Some of it leaks up through deep-sourced [[Hotspot (geology)|hotspot]] volcanoes such as those of the [[Hawaii]]an islands, but only 300 grams per year is emitted to the atmosphere. [[Mid-ocean ridge]]s emit another 3 kilogram per year. Around [[subduction|subduction zone]]s, 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.<ref>[[#Witt|Wittenberg 1994]] Page 3, Table 1. Page 9.</ref> Wittenberg cited Anderson's estimate of another 1200 metric tonnes in [[interplanetary dust]] particles on the ocean floors.<ref>[[#Witt|Wittenberg 1994]] Page A-1 citing Anderson 1993, "1200 metric tone"</ref> In the 1994 study, extracting helium-3 from these sources consumes more energy than fusion would release.<ref>[[#Witt|Wittenberg 1994]] Page A-4 "1 kg (3He), pumping power would be 1.13x10^6MYyr ... fusion power derived ... 19 MWyr"</ref> Wittenberg also writes that extraction from US crustal natural gas, consumes ten times the energy available from fusion reactions.<ref>[[#Witt|Wittenberg 1994]] Page A-4 using Table 1 page A-5 of US crustal natural gas</ref>{{Clarifyme|date=July 2008}}

==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.<ref>[http://www.cerncourier.com/main/article/41/8/14 Take a deep breath of nuclear spin - CERN Courier]</ref>

==Extraterrestrial supplies==
The [[Moon]]'s surface contains helium-3 at concentrations on the order of 0.01 [[Parts-per notation|ppm]].<ref>[http://fti.neep.wisc.edu/Research/he3_pubs.html FTI Research Projects :: 3He Lunar Mining]</ref><ref>{{cite web | url= http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf |format=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}}</ref> A number of people, starting with [[Gerald Kulcinski]] in 1986,<ref>{{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}}</ref> have proposed to [[Exploration of the Moon|explore the moon]], mine lunar [[regolith]] and using the helium-3 for [[Nuclear fusion|fusion]]. Because of the low concentrations of helium-3, any mining equipment would need to process large amounts of regolith,<ref>{{cite web | title = The challenge of mining He-3 on the lunar surface: how all the parts fit together | author = I.N. Sviatoslavsky | month = November | year = 1993 | url = http://fti.neep.wisc.edu/pdf/wcsar9311-2.pdf |format=PDF}} Wisconsin Center for Space Automation and Robotics Technical Report WCSAR-TR-AR3-9311-2.</ref> and some proposals have suggested that helium-3 extraction be piggybacked onto a larger mining and development operation.{{Fact|date=August 2007}}

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.<ref> {{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 }}</ref> 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.<ref>http://www.isro.org/chandrayaan/htmls/objective_scientific.htm</ref> <ref>http://luna-ci.blogspot.com/2008/11/chandrayaan-1-payload-feature-2-sub-kev.html</ref>

[[Cosmochemistry|Cosmochemist]] and [[geochemist]] [[Ouyang Ziyuan]] from the [[Chinese Academy of Sciences]] who is now in charge of the [[Chang'e program|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."<ref>[http://www.chinadaily.com.cn/cndy/2006-07/26/content_649325.htm He asked for the moon-and got it]</ref>

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,<ref>[http://www.space.com/news/ap_060126_russia_moon.html SPACE.com - Russian Rocket Builder Aims for Moon Base by 2015, Reports Say]</ref> if funding can be found.<ref>{{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}}</ref><ref>{{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}}</ref>

Mining [[gas giant]]s for helium-3 has also been proposed.<ref>{{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 |format=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.</ref> The [[British Interplanetary Society]]'s hypothetical [[Project Daedalus]] interstellar 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.

==Power generation==
A second-generation approach to controlled [[nuclear fusion|fusion]] power involves combining helium-3 ([[Helium-3|32He]]) and [[deuterium]] ([[Deuterium|21H]]). This reaction produces an [[helium-4]] ion ([[Helium-4|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 [[ion]]s 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 [[turbine]]-powered [[Electrical generator|generators]].

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 cost]]s 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 (economics)|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 1000-[[megawatt]] plants were on line, replacing old conventional plants or meeting new demand.<ref> {{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 }} </ref>

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 [[ITER]] and other [[tokamak]]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<ref>{{cite news | url = http://www.iter.org/Future-beyond.htm | title = Beyond ITER | accessdate = 2007-05-07}}</ref>. 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 [[Aneutronic fusion#Candidate aneutronic reactions|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<ref>{{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}}</ref>, 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 fusion|aneutronic]]" fuels. However, these systems would scale well enough that their proponents tend to promote [[Aneutronic fusion#Technical challenges|p-B fusion]], which requires no exotic fuels like He-3.

==See also==
*[[Moon]]

==Notes and references==
{{reflist}}
* <cite id=Smith>{{cite paper
|author=D.M Smith, T.W. Goodwin, J.A.Schiller
|date=
|url=http://www.airproducts.com/NR/rdonlyres/E44F8293-1CEE-4D80-86EA-F9815927BE7E/0/ChallengestoHeliumSupply111003.pdf
|format=pdf
|title=CHALLENGES TO THE WORLDWIDE SUPPLY OF HELIUM IN THE NEXT DECADE
|publisher=Air Products and Chemicals, Inc
|version=
|accessdate=2008-07-01
}}</cite>
* <cite id=Witt>{{cite paper
|author=L.J. Wittenberg
|date=July 1994
|url=http://fti.neep.wisc.edu/pdf/fdm967.pdf
|format=pdf
|title=Non-Lunar 3He Resources
|publisher=
|version=
|accessdate=2008-07-01
}}</cite>

==External links==
*[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]

{{Isotope|element=Helium
|lighter=[[Diproton]]
|heavier=[[Helium-4]]
|before=[[Lithium-4]] '''([[proton emission|p]]) '''[[Hydrogen-3]] '''([[beta decay|β−]])
|after=Stable
}}

[[Category:Isotopes of helium]]
[[Category:Nuclear fusion fuels]]
[[Category:Space exploration]]

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[[sv:Helium-3]]
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