Editing Tetraneutron

{{Short description|Hypothesised nuclear physics particle}}
The '''tetraneutron''' is considered an unbound isotope with a lifetime around 10<sup>−22</sup> seconds.<ref name=ThoennessenReview>{{Cite book |last=Thoennessen |first=Michael |title=The Discovery of Isotopes |chapter-url=http://link.springer.com/10.1007/978-3-319-31763-2_16 |chapter=Unbound Isotopes |date=2016 |publisher=Springer International Publishing |isbn=978-3-319-31761-8 |location=Cham |pages=275–291 |language=en |doi=10.1007/978-3-319-31763-2_16}}</ref>{{rp|275}} The stability of this cluster of four [[neutron]]s is not supported by current models of [[nuclear physics|nuclear]] forces.<ref name=cierjacks65>{{cite journal
 |last            = Cierjacks
 |first           = S.
 |display-authors = etal
 |year            = 1965
 |title           = Further Evidence for the Nonexistence of Particle-Stable Tetraneutrons
 |journal         = [[Physical Review]]
 |volume          = 137
 |issue           = 2B
 |pages           = 345–346
 |doi             = 10.1103/PhysRev.137.B345
 |bibcode         = 1965PhRv..137..345C
 |url             = https://publikationen.bibliothek.kit.edu/270000948/3809443
}}</ref> Recent [[empirical]] evidence is "consistent with a quasi-bound tetraneutron state existing for a very short time".<ref name=DuerNature2022/>

== Marqués' experiment ==
[[Francisco-Miguel Marques|Francisco-Miguel Marqués]] and co-workers at the [[Grand Accélérateur National d'Ions Lourds|GANIL]] accelerator in [[Caen]] used a [[particle accelerator]] to fire atomic nuclei at carbon targets and observed the "spray" of particles from the resulting collisions.<ref>{{Cite journal |last1=Marqués |first1=F. Miguel |last2=Carbonell |first2=Jaume |date=March 2021 |title=The quest for light multineutron systems |url=https://link.springer.com/10.1140/epja/s10050-021-00417-8 |journal=The European Physical Journal A |language=en |volume=57 |issue=3 |page=105 |doi=10.1140/epja/s10050-021-00417-8 |issn=1434-6001|arxiv=2102.10879 |bibcode=2021EPJA...57..105M |s2cid=231986449 }}</ref> In this case the experiment involved firing [[beryllium-14]], [[boron-15]] and [[lithium-11]] nuclei at a small [[carbon]] target, the most successful being beryllium-14. This isotope of beryllium has a [[nuclear halo]] that consists of four clustered neutrons; this allows it to be easily separated intact in the high-speed collision with the carbon target.<ref name="marques02">{{Cite journal |last1=Marqués |first1=F. M. |last2=Labiche |first2=M. |last3=Orr |first3=N. A. |last4=Angélique |first4=J. C. |last5=Axelsson |first5=L. |last6=Benoit |first6=B. |last7=Bergmann |first7=U. C. |last8=Borge |first8=M. J. G. |last9=Catford |first9=W. N. |last10=Chappell |first10=S. P. G. |last11=Clarke |first11=N. M. |last12=Costa |first12=G. |last13=Curtis |first13=N. |last14=D’Arrigo |first14=A. |last15=de Góes Brennand |first15=E. |date=2002-04-01 |title=Detection of neutron clusters |url=https://link.aps.org/doi/10.1103/PhysRevC.65.044006 |journal=Physical Review C |language=en |volume=65 |issue=4 |page=044006 |doi=10.1103/PhysRevC.65.044006 |issn=0556-2813|arxiv=nucl-ex/0111001 |bibcode=2002PhRvC..65d4006M |s2cid=37431352 }}</ref> Current nuclear models suggest that four separate neutrons should result when [[beryllium-10]] is produced, but the single signal detected in the production of beryllium-10 suggested a multineutron cluster in the breakup products; most likely a beryllium-10 nucleus and four neutrons fused together into a tetraneutron.

A later analysis of the method used in the Marqués' experiment suggested that the detection mechanism was unlikely<ref name="sherrill04">{{cite journal
 | last1 = Sherrill | first1 = B. M. 
 | last2 = Bertulani | first2= C. A
 | year = 2004
 | title = Proton-tetraneutron elastic scattering
 | journal = [[Physical Review C]]
 | volume = 69 | issue = 2 | pages = 027601
 | doi = 10.1103/PhysRevC.69.027601
 | arxiv = nucl-th/0312110 |bibcode = 2004PhRvC..69b7601S | s2cid = 26590179 
}}</ref> but the suggestion was refuted,<ref name="marques05">{{cite arXiv
 | last = Marqués | first = F. M. 
 | display-authors= etal 
 | year = 2005
 | title = On the possible detection of <sup>4</sup>n events in the breakup of <sup>14</sup>Be
 |eprint = nucl-ex/0504009v1 
}}</ref> and attempts to reproduce these observations with different methods have not successfully detected any neutron clusters.<ref name="aleksandrov05">{{cite journal
 | last = Aleksandrov | first = D. V.
 | display-authors= etal 
 | year = 2005
 | title = Search for Resonances in the Three- and Four-Neutron Systems in the <sup>7</sup>Li (<sup>7</sup>Li, <sup>11</sup>C) 3''n'' and <sup>7</sup>Li (<sup>7</sup>Li, <sup>10</sup>C) 4''n'' Reactions
 | journal = [[JETP Letters]]
 | volume = 81 | issue = 2 | pages = 43–46
 | doi = 10.1134/1.1887912
 | bibcode = 2005JETPL..81...43A 
 | s2cid = 121267804
}}</ref>

== Consequences of hypothetical bound tetraneutrons==
If, however, the existence of bound tetraneutrons were ever independently confirmed, considerable adjustments would have to be made to current nuclear models.  Bertulani and Zelevinsky proposed that, if it existed, the tetraneutron could be formed by a bound state of two [[dineutron]] systems.<ref name="bz03">
{{cite journal
 | last1 = Bertulani | first1 = C. A.
 | last2 = Zelevinsky |first2 = V. G.
 | year = 2003
 | title = Tetraneutron as a dineutron-dineutron molecule
 | journal = [[Journal of Physics G]]
 | volume = 29 | pages = 2431–2437
 | doi = 10.1088/0954-3899/29/10/309
 | arxiv= nucl-th/0212060
 | bibcode = 2003JPhG...29.2431B
 | issue = 10
 | s2cid = 55535943
}}</ref> However, attempts to model interactions that might give rise to multineutron clusters have failed,<ref name="lazauskas05">{{cite journal
 | last1 = Lazauskas | first1 = R.
 | last2 = Carbonell | first2 = J.
 | year = 2005
 | title = Three-neutron resonance trajectories for realistic interaction models
 | journal = [[Physical Review C]]
 | volume = 71 | pages = 044004 
 | doi = 10.1103/PhysRevC.71.044004
 | arxiv= nucl-th/0502037v2
 | bibcode = 2005PhRvC..71d4004L
 | issue = 4 | s2cid = 119105439
}}</ref><ref name="arai03">{{cite journal
 | last = Arai | first = K.
 | year = 2003
 | title = Resonance states of <sup>5</sup>H and <sup>5</sup>Be in a microscopic three-cluster model
 | journal = [[Physical Review C]]
 | volume = 68 | issue = 3 | pages = 034303 
 | doi = 10.1103/PhysRevC.68.034303
 |bibcode = 2003PhRvC..68c4303A
}}</ref><ref name="hemmdan02">{{cite journal
 | last1 = Hemmdan | first1 = A.
 | last2 = Glöckle | first2 = W. 
 | last3 = Kamada | first3= H.
 | year = 2002
 | title = Indications for the nonexistence of three-neutron resonances near the physical region
 | journal = [[Physical Review C]]
 | volume = 66 | issue = 3 | pages = 054001
 | doi = 10.1103/PhysRevC.66.054001
 | arxiv=nucl-th/0208007
 | bibcode = 2002PhRvC..66e4001H
 | s2cid = 11852197
}}</ref> and it "does not seem possible to change modern nuclear Hamiltonians to bind a tetraneutron without destroying many other successful predictions of those Hamiltonians. This means that, should a recent experimental claim of a bound tetraneutron be confirmed, our understanding of nuclear forces will have to be significantly changed."<ref name="pieper03">
{{cite journal
 | last = Pieper | first = S. C.
 | year = 2003
 | title = Can Modern Nuclear Hamiltonians Tolerate a Bound Tetraneutron?
 | journal = [[Physical Review Letters]]
 | volume = 90 | issue = 25 | pages = 252501 
 | doi = 10.1103/PhysRevLett.90.252501
 | arxiv=nucl-th/0302048
 | bibcode=2003PhRvL..90y2501P
 | pmid=12857127
 | s2cid = 31164554
}}</ref> 
Further work<ref name="Arxiv2019">{{cite journal
 | year = 2019
 | title = Tetraneutron condensation in neutron rich matter
 | last1 = Ivanytskyi | first1 = O.
 | last2 = Ángeles Pérez-García | first2 = M.
 | last3 = Albertus | first3 = C.
 | journal = European Physical Journal A
 | volume = 55 | issue = 10| pages = 184
 | bibcode = 2019EPJA...55..184I
 | arxiv = 1904.11512
 | doi = 10.1140/epja/i2019-12900-6 | doi-access = free
 }}</ref> in 2019 suggests potentially observable consequences in [[neutron star]] crusts, if the tetraneutron exists.

== Evidence for very short lived resonances ==

In 2016, researchers at [[RIKEN]] in [[Wakō, Saitama|Wakō]], Japan observed evidence that the tetraneutron exists briefly as a [[resonance (particle physics)|resonance]]. They fired a beam of neutron-rich [[helium-8]] nuclei (two protons and six neutrons) at a liquid target composed of [[helium-4]] (two protons and two neutrons). Occasionally, the reaction produced [[beryllium-8]] nuclei with four protons and four neutrons, leaving four neutrons unaccounted for.  If a four-neutron nucleus did occur, it lasted for about 10<sup>−21</sup> seconds before decaying into other particles.<ref>{{Cite news
 | title = Physicists find signs of four-neutron nucleus
 | last = Grant | first = Andrew
 | website = Science News
 | url = https://www.sciencenews.org/article/physicists-find-signs-four-neutron-nucleus
 | date= 8 February 2016
 | access-date = 8 February 2016
}}</ref><ref>{{Cite journal
 | title = Four neutrons together momentarily
 | last1 = Bertulani | first1 = Carlos A.
 | last2 = Zelevinsky | first2 = Vladimir
 | journal= Nature
 | year = 2016 | volume= 532 |issue = 7600 |pages= 448–449
 | doi = 10.1038/nature17884 | doi-access = free
 | pmid = 27049938
 | bibcode= 2016Natur.532..448B
}}</ref><ref name=Kisamori>{{cite journal
 | last1 = Kisamori | first1 = K.
 | display-authors= etal
 | journal = Physical Review Letters 
 | title = Candidate Resonant Tetraneutron State Populated by the <sup>4</sup>He(<sup>8</sup>He,<sup>8</sup>Be) Reaction
 | year = 2016
 | volume = 116 | issue = 5
 | page = 052501
 | doi = 10.1103/PhysRevLett.116.052501
| pmid = 26894705
 | bibcode = 2016PhRvL.116e2501K
 }}</ref>

Evidence for unbound clusters of 4 neutrons resonances in the disintegration of [[beryllium]]-14 nuclei,<ref name="marques02"/> in <sup>8</sup>He-<sup>8</sup>Be interactions,<ref name="Kisamori"/> and collisions of <sup>4</sup>He nuclei  give an estimated lifetime around 10<sup>−22</sup> seconds.<ref name=DuerNature2022>{{Cite journal |last1=Duer |first1=M. |last2=Aumann |first2=T. |last3=Gernhäuser |first3=R. |last4=Panin |first4=V. |last5=Paschalis |first5=S. |last6=Rossi |first6=D. M. |last7=Achouri |first7=N. L. |last8=Ahn |first8=D. |last9=Baba |first9=H. |last10=Bertulani |first10=C. A. |last11=Böhmer |first11=M. |last12=Boretzky |first12=K. |last13=Caesar |first13=C. |last14=Chiga |first14=N. |last15=Corsi |first15=A. |date=2022-06-23 |title=Observation of a correlated free four-neutron system |journal=Nature |language=en |volume=606 |issue=7915 |pages=678–682 |doi=10.1038/s41586-022-04827-6 |issn=0028-0836 |pmc=9217746 |pmid=35732764|bibcode=2022Natur.606..678D }}</ref>
These discoveries should deepen our understanding of the nuclear forces.<ref name="sciencealert">{{cite web|url=https://www.sciencenews.org/article/physicists-find-signs-four-neutron-nucleus|title=Physicists find signs of four-neutron nucleus|date=2016-02-24|access-date=2017-06-27|archive-date=2017-07-29|archive-url=https://web.archive.org/web/20170729030228/https://www.sciencenews.org/article/physicists-find-signs-four-neutron-nucleus|url-status=live}}</ref><ref>{{cite journal|first=Nigel|last=Orr|title=Can Four Neutrons Tango?|journal=[[Physics (American Physical Society magazine)|Physics]]|volume=9|date=2016-02-03|pages=14|doi=10.1103/Physics.9.14|bibcode=2016PhyOJ...9...14O|doi-access=free}}</ref>

== See also ==
* [[Neutronium]]
* [[Tetraquark]]

== Notes ==
{{reflist}}

== External links ==
* [https://web.archive.org/web/20021226013002/http://www.cnrs.fr/cw/en/pres/compress/noyau.htm Announcement of possible tetraneutron observations]
* [http://www.ganil.fr/user/news/com/com170402.html Announcement of possible tetraneutron observations] {{Webarchive|url=https://web.archive.org/web/20081125161235/http://www.ganil.fr/user/news/com/com170402.html |date=2008-11-25 }} {{in lang|fr}}
* [https://web.archive.org/web/20160303193644/http://www.cnrs.fr/cw/en/pres/compress/noyau.htm Announcement of possible tetraneutron observations (Internet Archive)]

[[Category:Hypothetical nuclei]]
[[Category:Neutron]]
[[Category:Isotopes of neutronium|Neutronium-4]]