neutronium n.

an extremely dense material composed entirely of free neutrons

In SF, neutronium is typically conceived of as a solid. Astrophysical research suggests that the condensed neutron material present in neutron stars is predominantly in a superfluid state.

[coined in German in 1926 by Andreas von Antropoff (Eine neue Form des periodischen Systems der Elementen, in Zeitschrift für Angewandte Chemie (vol. 39))]

Science

  • 1927 H. Gernsback Incredible Facts in Amazing Stories Jan. 877/1 page image Hugo Gernsback bibliography

    Scientists now have a substance called ‘Neutronium’, which we know exists in nature. This material weighs 60 million tons per cubic inch…. Neutronium is four trillion times as dense as water.

  • 1930 E. E. Smith Skylark Three in Amazing Stories Sept. 564/1 page image Edward E. Smith bibliography

    We're going to project a fourth-order force out to grab us some dense material, a pretty close approach to pure neutronium.

  • 1930 E. E. Smith Skylark Three in Amazing Stories Sept. 564/1 page image Edward E. Smith bibliography

    ‘Neutronium? Pure mass?…I have been under the impression that it does not exist. Of what use can such a substance be to you?’ ‘Can’t get pure neutronium, of course…couldn’t use it if we could. What we need and are going to get is a material of about two and a half million specific gravity.’

  • 1931 J. Williamson The Stone from the Green Star in Amazing Stories Nov. 748/1 page image Jack Williamson bibliography

    Thanks to her indestructible neutronium hull, the flier was not injured.

  • 1935 ‘M. Leinster’ Proxima Centauri in Astounding Stories Mar. 43/2 page image Murray Leinster bibliography

    He’d explain the disintegration field, which collapses the electrons of hydrogen so that it rises in atomic weight to helium, and the helium to lithium, while the oxygen of the water is split literally into neutronium and pure force.

  • 1942 ‘H. Clement’ Proof in Astounding Science Fiction June 103/1 page image Hal Clement bibliography

    The first cities were of neutronium, like those of today, but it was necessary to stabilize the neutrons with fields of energy; at core temperature, as you know, neutronium is a gas.

  • 1949 F. Brown Gateway to Darkness in Super Science Stories Nov. 22/1 page image Fredric Brown bibliography

    It negates the force that holds the electrons to the nucleus. In effect, it collapses matter into neutronium.

  • 1966 L. Niven Neutron Star in Worlds of If Oct. 18/2 page image Larry Niven bibliography

    The rocket motor would send the Skydiver crashing into eleven miles of neutronium.

  • 1977 J. Varley Ophiuchi Hotline (1994) 18 John Varley bibliography

    Far down the slope of the hole, halfway to infinity, a tiny mass of neutronium that had been Lilo was orbiting at almost the speed of light, releasing energy as it was stressed to the limits of matter before it finally decayed into oblivion.

  • 1981 T. Pratchett Strata 19 page image Terry Pratchett bibliography

    You plate the underside with neutronium for gravity.

  • 1984 D. Duane My Enemy, My Ally xii. 190 Diane Duane bibliography

    McCoy…timed about half his pieces out, preparing to dump them on her like a ton of neutronium in six very visible moves.

  • 1996 J. Gunn Joy Machine xiv. 209 James E. Gunn bibliography

    It wouldn’t be difficult to jury-rig a device—say an antimatter payload contained within a neutronium shell.

  • 2000 A. Reynolds Revelation Space xxviii. 376 Alastair Reynolds bibliography

    The relativistic projectile weapons were only slightly tardier, and reports of their success followed a few seconds later; spectacular stuttering pulses as the projectiles rained home, slugs of neutronium and antimatter slamming into the world.

  • 2012 R. Reed Noumenon in Asimov’s Science Fiction Sept. 59 page image Robert Reed bibliography

    So it isn’t a black hole…. And I don’t think it’s stabilized neutronium or some kind of strangelet stew either.

Research requirements

antedating 1930
Earliest cite

E.E. 'Doc' Smith, "Skylark Three"
Research History
Brian Ameringen submitted a 1949 cite from Fredric Brown.
Jonathan Stone posted a 1947 E.E. Smith cite to sci.physics that was verified and submitted by Mike Christie.
Steinn Sigurdsson suggested Baade & Zwicky's PNAS paper in about 1938, or Gamow in his book "Atomic Nuclei"; however, earlier cites have now been submitted, so we no longer need to find these references.
Mike Christie submitted a cite from a 1978 reprint of Murray Leinster's 1935 story "Proxima Centauri"; Alistair Durie verified this in its first magazine appearance.
Bill Seabrook located and Mike Christie confirmed a 1944 cite from Theodore Sturgeon's "Killdozer!"
Imran Ghory submitted a cite from a 1973 reprint of Isaac Asimov's "Black Friar of the Flame", which Fred Galvin verified in the 1942 first publication.
Rick Hauptmann submitted a 1931 cite from Jack Williamson's "The Stone from the Green Star".
Isaac Wilcott submitted a cite from the magazine serialization of E.E. Smith's "Skylark Three" (Amazing Stories, December 1930). Fred Galvin submitted cites from an earlier issues of the magazine serialization of E.E. Smith's "Skylark Three" (Amazing Stories, September 1930).
Clive Shergold submitted a 1981 cite from Terry Pratchett.

Earliest cite in the OED: 1967. Updated in September 2003 with a new earliest date of 1935. At some point thereafter, updated with the 1930 E. E. Smith cite.

Last modified 2025-01-25 03:44:26
In the compilation of some entries, HDSF has drawn extensively on corresponding entries in OED.