Editing Antimatter (section)

==Uses==

===Medical===
[[File:16slicePETCT.jpg|thumb|A PET/CT system]]
Matter–antimatter reactions have practical applications in medical imaging, such as [[positron emission tomography]] (PET). In positive [[beta decay]], a [[nuclide]] loses surplus positive charge by emitting a positron (in the same event, a proton becomes a neutron, and a [[neutrino]] is also emitted). Nuclides with surplus positive charge are easily made in a [[cyclotron]] and are widely generated for medical use. Antiprotons have also been shown within laboratory experiments to have the potential to treat certain cancers, in a similar method currently used for ion (proton) therapy.<ref>
{{cite journal
 |title=Antiproton portable traps and medical applications
 |journal=Hyperfine Interactions
 |volume=109
 |issue=1–4
 |pages=155
 |url=http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf
 |archive-url=https://web.archive.org/web/20110822150631/http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf
 |archive-date=22 August 2011
 |url-status=dead
|bibcode=1997HyInt.109..155L
 |last1=Lewis
 |first1=R. A.
 |last2=Smith
 |first2=G. A.
 |last3=Howe
 |first3=S. D.
 |year=1997
 |doi=10.1023/A:1012653416870
 |s2cid=120402661
 }}</ref>

===Fuel===<!-- This section is linked from [[Deuterium]] -->
Isolated and stored antimatter could be used as a [[fuel]] for [[interplanetary spaceflight|interplanetary]] or [[interstellar travel]]<ref>{{cite book
 |last=Schmidt |first=G. R.
 |title=35th Joint Propulsion Conference and Exhibit
 |date=1999
 |chapter=Antimatter Production for Near-Term Propulsion Applications
 |publisher=American Institute of Aeronautics and Astronautics
 |doi=10.2514/6.1999-2691
}}</ref> as part of an [[antimatter-catalyzed nuclear pulse propulsion]] or another [[antimatter rocket]]. Since the energy density of antimatter is higher than that of conventional fuels, an antimatter-fueled spacecraft would have a higher [[thrust-to-weight ratio]] than a conventional spacecraft.

If matter–antimatter collisions resulted only in [[photon]] emission, the entire [[rest mass]] of the particles would be converted to [[kinetic energy]]. The [[energy density|energy per unit mass]] ({{val|9|e=16|u=J/kg}}) is about 10 [[order of magnitude|orders of magnitude]] greater than [[chemical energy|chemical energies]],<ref>(compared to the [[heat of formation|formation]] of water at {{val|1.56|e=7|u=J/kg}}, for example)</ref> and about 3 orders of magnitude greater than the [[nuclear potential energy]] that can be liberated, today, using [[nuclear fission]] (about {{val|200|u=MeV}} per fission reaction<ref>{{cite web
 |last=Sowerby
 |first=M. G.
 |title=§4.7 Nuclear fission and fusion, and neutron interactions
 |url=http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html
 |work=Kaye & Laby: Table of Physical & Chemical Constants
 |publisher=[[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]
 |access-date=18 June 2010
 |archive-url=https://web.archive.org/web/20100305114800/http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html
 |archive-date=5 March 2010
 |url-status=dead
 }}</ref> or {{val|8|e=13|u=J/kg}}), and about 2 orders of magnitude greater than the best possible results expected from [[nuclear fusion|fusion]] (about {{val|6.3|e=14|u=J/kg}} for the [[proton–proton chain]]). The reaction of {{val|1|ul=kg}} of antimatter with {{val|1|u=kg}} of matter would produce {{val|1.8|e=17|ul=J}} (180 [[Orders of magnitude (energy)#1012 to 1017 J|petajoules]]) of energy (by the [[mass–energy equivalence]] formula, {{nowrap|1=''E''=''mc''<sup>2</sup>}}), or the rough equivalent of 43 megatons of TNT – slightly less than the yield of the 27,000&nbsp;kg [[Tsar Bomba]], the largest [[thermonuclear weapon]] ever detonated.

Not all of that energy can be utilized by any realistic propulsion technology because of the nature of the annihilation products. While electron–positron reactions result in gamma ray photons, these are difficult to direct and use for thrust. In reactions between protons and antiprotons, their energy is converted largely into relativistic neutral and charged [[pion]]s. The [[Pion#Neutral pion decays|neutral pions]] decay almost immediately (with a lifetime of 85 [[attoseconds]]) into high-energy photons, but the [[Pion#Charged pion decays|charged pions]] decay more slowly (with a lifetime of 26 nanoseconds) and can be [[Antimatter rocket#Direct use of reaction products|deflected magnetically to produce thrust]].

Charged pions ultimately decay into a combination of [[neutrino]]s (carrying about 22% of the energy of the charged pions) and unstable charged [[muon]]s (carrying about 78% of the charged pion energy), with the muons then decaying into a combination of electrons, positrons and neutrinos (cf. [[muon decay]]; the neutrinos from this decay carry about 2/3 of the energy of the muons, meaning that from the original charged pions, the total fraction of their energy converted to neutrinos by one route or another would be about {{nowrap|1=0.22 + (2/3)⋅0.78 = 0.74}}).<ref>
{{cite web
 |last=Borowski |first=S. K.
 |date=1987
 |title=Comparison of Fusion/Antiproton Propulsion systems
 |url=http://gltrs.grc.nasa.gov/reports/1996/TM-107030.pdf
 |pages=5–6 (pp. 6–7 of pdf)
 |work=NASA Technical Memorandum 107030
 |publisher=[[NASA]]
 |id=AIAA–87–1814
 |access-date=24 May 2008
 |archive-url=https://web.archive.org/web/20080528030524/http://gltrs.grc.nasa.gov/reports/1996/TM-107030.pdf
 |archive-date=28 May 2008
 |url-status=dead
}}</ref><!--

For more regular (earthly) applications (for example, regular transport, use in portable generators, and the powering of cities) artificially created antimatter is not a suitable energy carrier, despite its high energy density, because the process of creating antimatter is extremely inefficient. According to CERN, only one part in ten billion ({{val|e=-10}}) of the energy invested in the production of antimatter particles can be subsequently retrieved.<ref>
{{cite web
 |year=2004 [2008]
 |title=Angels and Demons: Inefficiency of Antimatter
 |url=http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |publisher=[[CERN]]
 |access-date=18 November 2010
 |archive-url=https://web.archive.org/web/20101116160609/http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |url-status=dead
 |archive-date=16 November 2010
}}</ref>

Antimatter production is currently very limited, but has been growing at a nearly [[geometric progression|geometric rate]] since the observation of the first antiproton in 1955 by Segrè and Chamberlain.<ref>
{{cite web
 |year=2006
 |title=1955: Emilio Segrè, Owen Chamberlain, and the matter of antimatter
 |url=http://sciencematters.berkeley.edu/archives/volume1/issue1/legacy.php
 |publisher=[[Regents of the University of California]]
 |access-date=18 November 2010
 |archive-url=https://web.archive.org/web/20100610093620/http://sciencematters.berkeley.edu/archives/volume1/issue1/legacy.php
 |url-status=dead
 |archive-date=10 June 2010
}}</ref> The current antimatter production rate is between 1 and 10 nanograms per year, and this is expected to increase to between 3 and 30 nanograms per year by 2015 or 2020 with new superconducting linear accelerator facilities at CERN and [[Fermilab]].

Some researchers{{Who|date=May 2012}} claim that with current technology, it is possible to obtain antimatter for [[United States dollar|US$]]25 million per gram by optimizing the collision and collection parameters (given current electricity generation costs).{{Citation needed|date=May 2012}}
Many experts{{Who|date=March 2011}}, however, dispute these claims as being far too optimistic by many orders of magnitude. They point out that, in 2004, the annual production of antiprotons at [[CERN]] was several picograms at a cost of $20 million. This means that to produce 1&nbsp;gram of antimatter, [[CERN]] would need to spend 100 quadrillion ({{val|e=17}}) dollars and run the antimatter factory for 100 billion years.

Antimatter production costs, in mass production, are almost linearly tied to electricity costs, so economical pure-antimatter thrust applications are unlikely to come online unless a very cheap power source is found.

Storage is another problem, as antiprotons are negatively charged and repel each other, so that they cannot be concentrated in a small volume (cf. [[space charge]]). [[Plasma oscillation]]s in the charged cloud of antiprotons can cause instabilities that drive antiprotons out of the storage trap. For these reasons, to date, only a few million antiprotons have been stored simultaneously in a magnetic trap, which corresponds to much less than a femtogram. Antihydrogen atoms or molecules are of neutral charge, they are not as ionically unstable as antiprotons. The drawback is that cold antihydrogen is far more complex to produce than mere antiprotons.

One researcher from the CERN laboratories, which produces antimatter regularly, said:
{{quote|If we could assemble all of the antimatter we've ever made at CERN and annihilate it with matter, we would have enough energy to light a single electric light bulb for a few minutes.<ref>
{{cite web
 |year=2004 [2008]
 |title=Angels and Demons: Do antimatter atoms exist?
 |url=http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |publisher=[[CERN]]
 |access-date=2010-11-18
 |archive-url=https://web.archive.org/web/20101116160609/http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |url-status=dead
 |archive-date=2010-11-16
}}</ref>}}
--->

===Weapons===
{{Main|Antimatter weapon}}

Antimatter has been considered as a trigger mechanism for nuclear weapons.<ref>
{{cite web
 |url=http://cui.unige.ch/isi/sscr/phys/anti-BPP-3.html
 |title=Antimatter weapons
 |archive-url=https://web.archive.org/web/20130424174413/http://cui.unige.ch/isi/sscr/phys/anti-BPP-3.html
 |archive-date=24 April 2013
 |url-status=live
}}</ref> A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it will ever be feasible.<ref>
{{Cite book
 |last1=Gsponer |first1=Andre
 |last2=Hurni |first2=Jean-Pierre
 |year=1987
 |chapter=The physics of antimatter induced fusion and thermonuclear explosions
 |editor1-last=Velarde |editor1-first=G.
 |editor2-last=Minguez |editor2-first=E.
 |title=Proceedings of the International Conference on Emerging Nuclear Energy Systems, Madrid, June/July, 1986
 |volume=4 |issue=30 |pages=66–169
 |publisher=[[World Scientific]]
 |arxiv=physics/0507114
 |bibcode=2005physics...7114G
}}</ref> Nonetheless, the [[United States Air Force|U.S. Air Force]] funded studies of the physics of antimatter in the [[Cold War]], and began considering its possible use in weapons, not just as a trigger, but as the explosive itself.<ref>
{{cite news
 |url=http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/10/04/MNGM393GPK1.DTL
 |title=Air Force pursuing antimatter weapons / Program was touted publicly, then came official gag order
 |newspaper=Sfgate
 |date=4 October 2004
 |archive-url=https://web.archive.org/web/20120609101650/http://www.sfgate.com/cgi-bin/article.cgi?file=%2Fc%2Fa%2F2004%2F10%2F04%2FMNGM393GPK1.DTL
 |archive-date=9 June 2012
 |url-status=live
|last1=Davidson
 |first1=Keay
 }}</ref>