Editing Neutronium (section)

===Scattering resonances with multiple neutrons===

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>{{cite journal | author = Schirber, M. | title = Nuclei Emit Paired-up Neutrons | journal = [[Physics (American Physical Society magazine)|Physics]] | date = 2012 | volume = 5 | page = 30 | doi = 10.1103/Physics.5.30 | bibcode = 2012PhyOJ...5...30S }}</ref><ref>{{cite journal | author = Spyrou, A. | display-authors = 4 | author2 = Kohley, Z. | author3 = Baumann, T. | author4 = Bazin, D. | author5 = Brown, B. A. | author6 = Christian, G. | author7 = DeYoung, P. A. | author8 = Finck, J. E. | author9 = Frank, N. | author10 = Lunderberg, E. | author11 = Mosby, S. | author12 = Peters, W. A. | author13 = Schiller, A. | author14 = Smith, J. K. | author15 = Snyder, J. | author16 = Strongman, M. J. | author17 = Thoennessen, M. | author18 = Volya, A. | title = First Observation of Ground State Dineutron Decay: <sup>16</sup>Be | journal = [[Physical Review Letters]] | date = 2012 | volume = 108 | issue = 10 | page = 102501 | doi = 10.1103/PhysRevLett.108.102501 | pmid = 22463404 | bibcode = 2012PhRvL.108j2501S | doi-access = free }}</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>{{Cite journal |last1=Monteagudo |first1=B. |last2=Marqués |first2=F. M. |last3=Gibelin |first3=J. |last4=Orr |first4=N. A. |last5=Corsi |first5=A. |last6=Kubota |first6=Y. |last7=Casal |first7=J. |last8=Gómez-Camacho |first8=J. |last9=Authelet |first9=G. |last10=Baba |first10=H. |last11=Caesar |first11=C. |last12=Calvet |first12=D. |last13=Delbart |first13=A. |last14=Dozono |first14=M. |last15=Feng |first15=J. |date=2024-02-23 |title=Mass, Spectroscopy, and Two-Neutron Decay of $^{16}\mathrm{Be}$ |url=https://eprints.whiterose.ac.uk/211204/1/2401.16817.pdf |journal=Physical Review Letters |volume=132 |issue=8 |pages=082501 |doi=10.1103/PhysRevLett.132.082501}}</ref>

The dineutron hypothesis had been used in theoretical studies of the structure of [[exotic nuclei]]. For example <sup>11</sup>Li is modeled as a dineutron bound to a <sup>9</sup>Li core.<ref name="Bertulani 1993 281–376">{{cite journal | last1 = Bertulani | first1 = C. A. | last2 = Canto | first2 = L. F. | last3 = Hussein | first3 = M. S. | title = The Structure And Reactions Of Neutron-Rich Nuclei | journal = [[Physics Reports]] | date = 1993 | volume = 226 | issue = 6 | pages = 281–376 | bibcode = 1993PhR...226..281B | doi = 10.1016/0370-1573(93)90128-Z | url = http://www.tamu-commerce.edu/physics/carlos/papers/PRep226_1993_281.pdf | archive-url = https://web.archive.org/web/20110928120249/http://www.tamu-commerce.edu/physics/carlos/papers/PRep226_1993_281.pdf | url-status = dead | archive-date = 2011-09-28 }}</ref><ref>{{cite journal | last1 = Hagino | first1 = K. | last2 = Sagawa | first2 = H. | last3 = Nakamura | first3 = T. | last4 = Shimoura | first4 = S. | title = Two-particle correlations in continuum dipole transitions in Borromean nuclei | journal = [[Physical Review C]] | date = 2009 | volume = 80 | issue = 3 | page = 1301 | arxiv = 0904.4775 | bibcode = 2009PhRvC..80c1301H | doi = 10.1103/PhysRevC.80.031301 | s2cid = 119293335 }}</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>{{cite journal | last1 = MacDonald | first1 = J. | last2 = Mullan | first2 = D. J. | date = 2009 | title = Big Bang Nucleosynthesis: The Strong Nuclear Force meets the Weak Anthropic Principle | journal = [[Physical Review D]] | volume = 80 | issue = 4 | page = 3507 | arxiv = 0904.1807 | bibcode = 2009PhRvD..80d3507M | doi = 10.1103/PhysRevD.80.043507 | s2cid = 119203730 }}</ref> This has some consequences on [[nucleosynthesis]] and the [[abundance of the chemical elements]].<ref name="Bertulani 1993 281–376"/><ref>{{cite journal | last1 = Kneller | first1 = J. P. | last2 = McLaughlin | first2 = G. C. | author2-link = Gail McLaughlin | title = The Effect of Bound Dineutrons upon BBN | journal = [[Physical Review D]] | date = 2004 | volume = 70 | issue = 4 | page = 3512 | arxiv = astro-ph/0312388 | bibcode = 2004PhRvD..70d3512K | doi = 10.1103/PhysRevD.70.043512 | s2cid = 119060865 }}</ref>

A trineutron state consisting of three bound neutrons has not been detected, and is not expected to be bound.<ref>{{cite journal |title=Ab initio no-core Gamow shell-model calculations of multineutron systems |first1=J. G. |last1=Li |first2=N. |last2=Michel |first3=B. S. |last3=Hu |first4=W. |last4=Zuo |first5=F. R. |last5=Xu |journal=Physical Review C |volume=100 |issue= 5|date=2019 |page=054313 |doi=10.1103/PhysRevC.100.054313 |arxiv=1911.06485|bibcode=2019PhRvC.100e4313L }}</ref>

A [[tetraneutron]] is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated.<ref>{{cite journal | last1 = Bertulani | first1 = C. A. | last2 = Zelevinsky | first2 = V. | year = 2003 | title = Is the tetraneutron a bound dineutron-dineutron molecule? | journal = [[Journal of Physics G]] | volume = 29 | issue = 10 | pages = 2431–2437 | arxiv = nucl-th/0212060 | bibcode = 2003JPhG...29.2431B | doi = 10.1088/0954-3899/29/10/309 | s2cid = 55535943 }}</ref><ref>[https://scitechdaily.com/tetra-neutron-experiment-understanding-of-nuclear-forces-might-have-to-be-significantly-changed/ "Tetra-Neutron Experiment: Understanding of Nuclear Forces Might Have To Be Significantly Changed"]. {{Webarchive|url=https://web.archive.org/web/20211213090609/https://scitechdaily.com/tetra-neutron-experiment-understanding-of-nuclear-forces-might-have-to-be-significantly-changed/ |date=2021-12-13 }}. 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>{{cite journal | last1 = Bevelacqua | first1 = J. J. | title = Particle stability of the pentaneutron | journal = [[Physics Letters B]] | date = 1981 | volume = 102 | issue = 2–3 | pages = 79–80 | bibcode = 1981PhLB..102...79B | doi = 10.1016/0370-2693(81)91033-9 }}</ref>