Neutronium is a proposed name for a substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the discovery of the neutron itself) for the conjectured "element of atomic number zero" that he placed at the head of the periodic table.[1][2] However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been used legitimately to refer to extremely dense phases of matter resembling the neutron-degenerate matter postulated to exist in the cores of neutron stars. Science fiction and popular literature frequently use the term "neutronium" to refer to a highly dense phase of matter composed primarily of neutrons.


Neutronium and neutron stars

Neutronium is used in popular literature to refer to the material present in the cores of neutron stars (stars which are too massive to be supported by electron degeneracy pressure and which collapse into a denser phase of matter). This term is very rarely used in scientific literature, for two reasons:

  • There is no universally agreed-upon definition for the term "neutronium".
  • There is considerable uncertainty over the composition of the material in the cores of neutron stars (it could be neutron-degenerate matter, strange matter, quark matter, or a variant or combination of the above).

When neutron star core material is presumed to consist mostly of free neutrons, it is typically referred to as neutron-degenerate matter in scientific literature.[3]

Neutronium and the periodic table

The term "neutronium" was coined in 1926 by Professor Andreas von Antropoff for a conjectured form of matter made up of neutrons with no protons, which he placed as the chemical element of atomic number zero at the head of his new version of the periodic table. It was subsequently placed in the middle of several spiral representations of the periodic system for classifying the chemical elements, such as those of Charles Janet (1928), E. I. Emerson (1944), John D. Clark (1950) and in Philip Stewart's Chemical Galaxy (2005).

Although the term is not used in the scientific literature either for a condensed form of matter, or as an element, there have been reports that, besides the free neutron, there may exist two bound forms of neutrons without protons.[4] However, these reports have not been further substantiated. Further information can be found in the following articles:

  • Mononeutron: Isolated neutrons undergo beta decay with a mean lifetime of approximately 15 minutes (half-life of approximately 10 minutes), becoming protons (the nucleus of hydrogen), electrons and antineutrinos.
  • Dineutron: The dineutron, containing two neutrons, is not a bound particle, but has been proposed as an extremely short-lived state produced by nuclear reactions involving tritium. It was suggested to have a transitory existence in nuclear reactions produced by helions that result in the formation of a proton and a nucleus having the same atomic number as the target nucleus but a mass number two units greater. The dineutron hypothesis has been used in nuclear reactions with exotic nuclei for a long time.[5] Several applications of the dineutron in nuclear reactions can be found in review papers.[6] Its existence has been proven to be relevant for nuclear structure of exotic nuclei.[7] A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so.[8] This has some consequences on nucleosynthesis and the abundance of the chemical elements.[6][9]
  • Trineutron: A trineutron state consisting of three bound neutrons has not been detected, and is not expected to exist even for a short time.
  • Tetraneutron: A tetraneutron is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated. If confirmed, it would require revision of current nuclear models.[10][11]
  • Pentaneutron: Calculations indicate that the hypothetical pentaneutron state, consisting of a cluster of five neutrons, would not be bound.
  • And so on, through the numbers, up to icosaneutron, with 20 neutrons.[12]

If one accepts neutronium to be an element, the above mentioned neutron clusters would be the isotopes of that element, if their existence can be confirmed. Also, if neutronium is accepted to be an element, it would not be a noble gas, for it would have no electrons, in fact, it would have no electron shells. All electron shells and their electrons have been squeezed out of the material by pressure. The material would, thus, like noble gasses be unreactive, but for different reasons. Neutronium would not fit anywhere in the periodic table. Although not called "neutronium", the National Nuclear Data Center's Nuclear Wallet Cards lists as its first "isotope" an "element" with the symbol n and atomic number Z = 0 and mass number A = 1. This isotope is described as decaying to element H with a half life of 10.24±0.02 minutes.

Neutronium in fiction

The term neutronium has been popular in science fiction since at least the middle of the 20th century. It typically refers to an extremely dense, incredibly strong form of matter. While presumably inspired by the concept of neutron-degenerate matter in the cores of neutron stars, the material used in fiction bears at most only a superficial resemblance, usually depicted as an extremely strong solid under Earth-like conditions, or possessing exotic properties such as the ability to manipulate time and space. In contrast, all proposed forms of neutron star core material are fluids and are extremely unstable at pressures lower than that found in stellar cores.

Noteworthy appearances of neutronium in fiction include the following:

  • In Hal Clement's short story Proof (1942), neutronium is the only form of solid matter known to Solarians, the inhabitants of the Sun's interior.
  • In Vladimir Savchenko's Black Stars (1960), neutronium is mechanically and thermally indestructible substance. It is also used to make antimatter, which leads to an annihilation accident.
  • In the commentary for the 2011 film Thor, director Kenneth Branagh hypothesized that Thor's Hammer is composed of neutronium, since it is explicitly stated in the film that the hammer was forged from a dying star. This would account for some of the hammer's properties such as its extreme weight.[citation needed]
  • In Doctor Who (1963), neutronium is a substance which can shield spaces from time-shear when used as shielding in time-vessels.
  • In Larry Niven's Known Space fictional universe (1964), neutronium is actual neutron star core material. Niven does not make assumptions about its strength, but imagines that small blobs of it could be artificially created under pressure, and their instability overcome by containing them in slaver stasis fields.
  • In the Star Trek universe, neutronium is an extremely hard and durable substance, often used as armor, which conventional weapons cannot penetrate or even dent.
  • In the Star Wars expanded universe, neutronium is a metal used to make the Durasteel alloy.[13]
  • In the computer games Master of Orion (1993), Master of Orion 2 (1996), Master of Orion 3 (2003), and Sid Meier's Alpha Centauri (1999), neutronium is one of the strongest armor types. MoO1 - strongest; MoO2 & SMAC - 3rd strongest. MoO1 and MoO2 also feature "neutronium bombs", which are extremely powerful planetary bombardment weapons which causes damage due to gravitic effects.
  • In Peter F. Hamilton's novel The Neutronium Alchemist (1997), neutronium is created by the "aggressive" setting of a superweapon.
  • In the Stargate universe, neutronium is a substance which is the basis of the technology of the advanced Asgard race, as well as a primary component of human-form Replicators; and apparently occurs naturally as a mineral in the crusts on some earthlike planets.
  • In Greg Bear's The Forge of God (1987), alien aggressors inject two high-mass weapons made of neutronium and antineutronium into the Earth which orbit the Earth's core until they meet and annihilate, destroying the planet.
  • In Howard Tayler's ongoing web-comic "Schlock Mercenary" (June 12, 2000 – Present) neutronium-fueled reactors (referred to as "Annie-plants", short for neutronium gravitic-annihilation power plant) are used to power everything including energy pistols, powered armor suits, whole worlds, and massive warships. The neutronium in these "evaporates" violently if the annie-plant is breached, but not violently enough to suggest any conversion to energy. It is stated that extremely large warships can use gravitic weaponry to literally crush smaller foes into neutronium, which they may then choose to use as fuel.

See also


  1. ^ von Antropoff, A. (1926). "Eine neue Form des periodischen Systems der Elementen". Zeitschrift für Angewandte Chemie 39 (23): 722–725. doi:10.1002/ange.19260392303. 
  2. ^ Stewart, P. J. (2007). "A century on from Dmitrii Mendeleev: Tables and spirals, noble gases and Nobel prizes". Foundations of Chemistry 9 (3): 235–245. doi:10.1007/s10698-007-9038-x. 
  3. ^ Angelo, J. A. (2006). Encyclopedia of space and astronomy. Infobase Publishing. ISBN 9780816053308. 
  4. ^ Timofeyuk, N. K. (2003). "Do multineutrons exist?". Journal of Physics G 29 (2): L9. arXiv:nucl-th/0301020. Bibcode 2003JPhG...29L...9T. doi:10.1088/0954-3899/29/2/102. 
  5. ^ Bertulani, C. A.; Baur, G. (1986). "Coincidence Cross-sections for the Dissociation of Light Ions in High-energy Collisions". Nuclear Physics A 480 (3–4): 615. Bibcode 1988NuPhA.480..615B. doi:10.1016/0375-9474(88)90467-8. 
  6. ^ a b Bertulani, C. A.; Canto, L. F.; Hussein, M. S. (1993). "The Structure And Reactions Of Neutron-Rich Nuclei". Physics Reports 226 (6): 281–376. Bibcode 1993PhR...226..281B. doi:10.1016/0370-1573(93)90128-Z. 
  7. ^ Hagino, K.; Sagawa, H.; Nakamura, T.; Shimoura, S. (2009). "Two-particle correlations in continuum dipole transitions in Borromean nuclei". Physical Review C 80 (3): 1301. arXiv:0904.4775. Bibcode 2009PhRvC..80c1301H. doi:10.1103/PhysRevC.80.031301. 
  8. ^ MacDonald, J.; Mullan, D. J. (2009). "Big Bang Nucleosynthesis: The Strong Nuclear Force meets the Weak Anthropic Principle". Physical Review D 80 (4): 3507. arXiv:0904.1807. Bibcode 2009PhRvD..80d3507M. doi:10.1103/PhysRevD.80.043507. 
  9. ^ Kneller, J. P.; McLaughlin, G. C. (2004). "The Effect of Bound Dineutrons upon BBN". Physical Review D 70 (4): 043512. arXiv:astro-ph/0312388. Bibcode 2004PhRvD..70d3512K. doi:10.1103/PhysRevD.70.043512. 
  10. ^ Bertulani, C. A.; Zelevinsky, V. (2002). "Is the tetraneutron a bound dineutron-dineutron molecule?". Journal of Physics G 29 (10): 2431. arXiv:nucl-th/0212060. Bibcode 2003JPhG...29.2431B. doi:10.1088/0954-3899/29/10/309. 
  11. ^ Timofeyuk, N. K. (2002). "On the existence of a bound tetraneutron". arXiv:nucl-th/0203003 [nucl-th]. 
  12. ^ Bevelacqua, J. J. (1981). "Particle stability of the pentaneutron". Physics Letters B 102 (2–3): 79–80. Bibcode 1981PhLB..102...79B. doi:10.1016/0370-2693(81)91033-9. 
  13. ^

Further reading

  • Glendenning, N. K. (2000). Compact Stars: Nuclear Physics, Particle Physics, and General Relativity (2nd ed.). Springer. ISBN 9780387989778. 

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