A tetraneutron is a hypothetical stable cluster of four neutrons. The existence of this cluster of particles is not supported by current models of nuclear forces.[1] There is some empirical evidence suggesting that this particle does exist, based on a 2001 experiment by Francisco-Miguel Marqués and co-workers at the Ganil accelerator in Caen using a novel detection method in observations of the disintegration of beryllium and lithium nuclei.[2] However, subsequent attempts to replicate this observation have failed.

Further work[3] in 2019 suggests potentially observable consequences in neutron star crusts, if the tetraneutron exists.

As detailed at the end of this article, subsequent observations from different ion beam experiments are consistent with short-lived four neutron states with some binding.

Overview

Tetraneutron is considered an unbound isotope with lifetimes around 10-22 seconds.[4]: 275  Evidence for unbound clusters of 4 neutrons resonances in the disintegration of beryllium-14 nuclei,[5] in 8He-8Be interactions,[6] and collisions of 4He nuclei give an estimated lifetime around 10-22 seconds.[7] These discoveries should deepen our understanding of the nuclear forces.[8][9]

Marqués' experiment

As with many particle accelerator experiments, Marques' team fired atomic nuclei at carbon targets and observed the "spray" of particles from the resulting collisions.[10] 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.[2] 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.

Since Marqués' experiment

A later analysis of the method used in the Marqués' experiment suggested that the detection mechanism was unlikely[11] but the suggestion was refuted,[12] and attempts to reproduce these observations with different methods have not successfully detected any neutron clusters.[13] If, however, the existence of stable 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.[14] However, attempts to model interactions that might give rise to multineutron clusters have failed,[15][16][17] 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."[18]

In 2016, researchers at RIKEN in Wakō, Japan observed evidence that the tetraneutron exists briefly as a 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 10−21 seconds before decaying into other particles.[19][20][21]

See also

Notes

  1. ↑ Cierjacks, S.; et al. (1965). "Further Evidence for the Nonexistence of Particle-Stable Tetraneutrons". Physical Review. 137 (2B): 345–346. Bibcode:1965PhRv..137..345C. doi:10.1103/PhysRev.137.B345.
  2. 1 2 Marqués, F. M.; et al. (2002). "Detection of neutron clusters". Physical Review C. 65 (4): 044006. arXiv:nucl-ex/0111001. Bibcode:2002PhRvC..65d4006M. doi:10.1103/PhysRevC.65.044006. S2CID 37431352.
  3. ↑ Ivanytskyi, O.; Ángeles Pérez-García, M.; Albertus, C. (2019). "Tetraneutron condensation in neutron rich matter". European Physical Journal A. 55 (10): 184. arXiv:1904.11512. Bibcode:2019EPJA...55..184I. doi:10.1140/epja/i2019-12900-6.
  4. ↑ Thoennessen, Michael (2016). Unbound Isotopes. Cham: Springer International Publishing. pp. 275–291. doi:10.1007/978-3-319-31763-2_16. ISBN 978-3-319-31761-8.
  5. ↑ Marqués, F. M.; Labiche, M.; Orr, N. A.; Angélique, J. C.; Axelsson, L.; Benoit, B.; Bergmann, U. C.; Borge, M. J. G.; Catford, W. N.; Chappell, S. P. G.; Clarke, N. M.; Costa, G.; Curtis, N.; D’Arrigo, A.; de Góes Brennand, E. (2002-04-01). "Detection of neutron clusters". Physical Review C. 65 (4). arXiv:nucl-ex/0111001. doi:10.1103/PhysRevC.65.044006. ISSN 0556-2813.
  6. ↑ Kisamori, K.; et al. (2016). "Candidate Resonant Tetraneutron State Populated by the He4(He8,Be8) Reaction". Physical Review Letters. 116 (5): 052501. Bibcode:2016PhRvL.116e2501K. doi:10.1103/PhysRevLett.116.052501. PMID 26894705.
  7. ↑ Duer, M.; Aumann, T.; Gernhäuser, R.; Panin, V.; Paschalis, S.; Rossi, D. M.; Achouri, N. L.; Ahn, D.; Baba, H.; Bertulani, C. A.; Böhmer, M.; Boretzky, K.; Caesar, C.; Chiga, N.; Corsi, A. (2022-06-23). "Observation of a correlated free four-neutron system". Nature. 606 (7915): 678–682. doi:10.1038/s41586-022-04827-6. ISSN 0028-0836. PMC 9217746. PMID 35732764.
  8. ↑ "Physicists find signs of four-neutron nucleus". 2016-02-24. Archived from the original on 2017-07-29. Retrieved 2017-06-27.
  9. ↑ Orr, Nigel (2016-02-03). "Can Four Neutrons Tango?". Physics. 9: 14. Bibcode:2016PhyOJ...9...14O. doi:10.1103/Physics.9.14.
  10. ↑ Marqués, F. Miguel; Carbonell, Jaume (March 2021). "The quest for light multineutron systems". The European Physical Journal A. 57 (3). arXiv:2102.10879. doi:10.1140/epja/s10050-021-00417-8. ISSN 1434-6001.
  11. ↑ Sherrill, B. M.; Bertulani, C. A (2004). "Proton-tetraneutron elastic scattering". Physical Review C. 69 (2): 027601. arXiv:nucl-th/0312110. Bibcode:2004PhRvC..69b7601S. doi:10.1103/PhysRevC.69.027601. S2CID 26590179.
  12. ↑ Marqués, F. M.; et al. (2005). "On the possible detection of 4n events in the breakup of 14Be". arXiv:nucl-ex/0504009v1.
  13. ↑ Aleksandrov, D. V.; et al. (2005). "Search for Resonances in the Three- and Four-Neutron Systems in the 7Li (7Li, 11C) 3n and 7Li (7Li, 10C) 4n Reactions". JETP Letters. 81 (2): 43–46. Bibcode:2005JETPL..81...43A. doi:10.1134/1.1887912. S2CID 121267804.
  14. ↑ Bertulani, C. A.; Zelevinsky, V. G. (2003). "Tetraneutron as a dineutron-dineutron molecule". Journal of Physics G. 29 (10): 2431–2437. arXiv:nucl-th/0212060. Bibcode:2003JPhG...29.2431B. doi:10.1088/0954-3899/29/10/309. S2CID 55535943.
  15. ↑ Lazauskas, R.; Carbonell, J. (2005). "Three-neutron resonance trajectories for realistic interaction models". Physical Review C. 71 (4): 044004. arXiv:nucl-th/0502037v2. Bibcode:2005PhRvC..71d4004L. doi:10.1103/PhysRevC.71.044004. S2CID 119105439.
  16. ↑ Arai, K. (2003). "Resonance states of 5H and 5Be in a microscopic three-cluster model". Physical Review C. 68 (3): 034303. Bibcode:2003PhRvC..68c4303A. doi:10.1103/PhysRevC.68.034303.
  17. ↑ Hemmdan, A.; Glöckle, W.; Kamada, H. (2002). "Indications for the nonexistence of three-neutron resonances near the physical region". Physical Review C. 66 (3): 054001. arXiv:nucl-th/0208007. Bibcode:2002PhRvC..66e4001H. doi:10.1103/PhysRevC.66.054001. S2CID 11852197.
  18. ↑ Pieper, S. C. (2003). "Can Modern Nuclear Hamiltonians Tolerate a Bound Tetraneutron?". Physical Review Letters. 90 (25): 252501. arXiv:nucl-th/0302048. Bibcode:2003PhRvL..90y2501P. doi:10.1103/PhysRevLett.90.252501. PMID 12857127. S2CID 31164554.
  19. ↑ Grant, Andrew (8 February 2016). "Physicists find signs of four-neutron nucleus". Science News. Retrieved 8 February 2016.
  20. ↑ Bertulani, Carlos A.; Zelevinsky, Vladimir (2016). "Four neutrons together momentarily". Nature. 532 (7600): 448–449. Bibcode:2016Natur.532..448B. doi:10.1038/nature17884. PMID 27049938.
  21. ↑ Kisamori, K.; et al. (2016). "Candidate Resonant Tetraneutron State Populated by the 4He(8He,8Be) Reaction". Physical Review Letters. 116 (5): 052501. Bibcode:2016PhRvL.116e2501K. doi:10.1103/PhysRevLett.116.052501. PMID 26894705.
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