Neutronium (or neutrium,<ref name=InglisArkell>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> neutrite,<ref name="Zhuravleva">Template:Cite book</ref> or element zero) is a hypothetical substance made purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the 1932 discovery of the neutron) for the hypothetical "element of atomic number zero" (with no protons in its nucleus) that he placed at the head of the periodic table (denoted by -).<ref name='Antropoff 1926'>Template:Cite journal</ref><ref name='Stewart 2007'>Template:Cite journal</ref> However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been also used to refer to extremely dense substances resembling the neutron-degenerate matter theorized to exist in the cores of neutron stars.
In neutron starsEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}
Neutronium is used in popular physics literature<ref name=InglisArkell/><ref name=Zhuravleva/> 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). In scientific literature the term "neutron-degenerate matter"<ref>Template:Cite book</ref> or simply neutron matter is used for this material.<ref>Template:Cite journal</ref>
Hypothetical multi-neutronsEdit
The term "neutronium" was coined in 1926 by Andreas von Antropoff for a conjectured form of matter made up of neutrons with no protons or electrons, which he placed as the chemical element of atomic number zero at the head of his new version of the periodic table.<ref name='Antropoff 1926'/> 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), Edgar Emerson (1944),<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> and John D. Clark (1950).
Template:AnchorThe term is not used in the scientific literature either for a condensed form of matter, or as an element, and theoretical analysis expects no bound forms of neutrons without protons.<ref>Template:Cite journal</ref>
Scattering resonances with multiple neutronsEdit
The dineutron, containing two neutrons, is not a stable bound particle, but an extremely short-lived resonance state produced by nuclear reactions in the decay of beryllium-16. Evidence reported in 2012 for the resonance<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> was disputed,<ref>Marqués, F. M., Orr, N. A., Achouri, N. L., Delaunay, F., & Gibelin, J. (2012). Comment on “First Observation of Ground State Dineutron Decay: Be 16”. Physical Review Letters, 109(23), 239201.</ref> but new work reportedly clears up the issues.<ref>Template:Cite journal</ref>
The dineutron hypothesis had been used in theoretical studies of the structure of exotic nuclei. For example 11Li is modeled as a dineutron bound to a 9Li core.<ref name="Bertulani 1993 281–376">Template:Cite journal</ref><ref>Template:Cite journal</ref> A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so.<ref>Template:Cite journal</ref> This has some consequences on nucleosynthesis and the abundance of the chemical elements.<ref name="Bertulani 1993 281–376"/><ref>Template:Cite journal</ref>
A trineutron state consisting of three bound neutrons has not been detected, and is not expected to be bound.<ref>Template:Cite journal</ref>
A tetraneutron is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated.<ref>Template:Cite journal</ref><ref>"Tetra-Neutron Experiment: Understanding of Nuclear Forces Might Have To Be Significantly Changed". Template:Webarchive. SciTechDaily, December 12, 2021. Technical University of Munich (TUM)</ref>
Calculations indicate that the hypothetical pentaneutron state, consisting of a cluster of five neutrons, would not be bound.<ref>Template:Cite journal</ref>
See alsoEdit
ReferencesEdit
Template:Periodic table (navbox) Template:Neutron star Template:Portal bar