- Tetraneutron
A tetraneutron is a hypothesised stable cluster of four
neutron s. This cluster of particles is not supported by current models of nuclear forces. [Cierjacks, S. "et al." (January 1965) "Further Evidence for the Nonexistence of Particle-Stable Tetraneutrons" "Physical Review" 137(2B): pp. 345-346] However, there is someempirical evidence which suggests this particle does exist, based on an experiment by Francisco-Miguel Marqués and co-workers at theGanil accelerator inCaen using a novel detection method in observations of the disintegration ofberyllium andlithium nuclei.F. M. Marqués "et al." (April 2002) "Detection of neutron clusters" "Physical Review" C 65, 044006, DOI: 10.1103/PhysRevC.65.044006 ] Subsequent attempts to replicate this observation have failed.Confirmation of the existence of a tetraneutron would be a significant discovery because current nuclear theory suggests that these clusters should not be stable, and thus should not exist. If it does, then it has been suggested that the substance be considered an "element", and be placed on the
Periodic Table of the Elements , with anatomic number of 0 (zero).Marqués' experiment
As with many
particle accelerator experiments, Marques' team fired atomic nuclei at one another and observed the 'spray' of particles from the resulting collisions. In this case the experiment involved firingberyllium -14, beryllium-15 andlithium -11 nuclei at a smallcarbon target, the most successful beingberyllium -14. This isotope of beryllium has anuclear halo that consists of four clustered neutrons; this allows it to be easily separated intact in the high speed collision with the carbon target. Their approach to the production and detection of bound neutron clusters was new and novel. Current nuclear models suggest that four separate neutrons should result when beryllium-10 is produced, but the 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 detection method used in the Marques' experiment suggested that at least part of the original analysis was flawedB. M. Sherrill and C. A. Bertulani, Proton-tetraneutron elastic scattering, Phys. Rev. C 69, 027601 (2004)] , and attempts to reproduce these observations with different methods have not successfully detected any neutron clusters.D. V. Aleksandrov, et al. 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, 43 (2005)] If, however, the existence of stable tetraneutrons was ever independently confirmed, considerable adjustments would have to be made to current nuclear models. Bertulani and ZelevinskyC.A. Bertulani and V.G. Zelevinsky, Tetraneutron as a dineutron-dineutron molecule, J. Phys. G 29 (2003) 2431] proposed that, if it existed, the tetraneutron could be formed by a bound state of two dineutron molecules. However, attempts to model interactions which might give rise to multineutron clusters have failed,Rimantas Lazauskas, and Jaume Carbonell, Three-neutron resonance trajectories for realistic interaction models, Phys. Rev. C 71, 044004 (2005)] Koji Arai, Resonance states of 5H and 5Be in a microscopic three-cluster model, Phys. Rev. C 68, 034303 (2003)] A. Hemmdan, W. Glöckle, and H. Kamada, Indications for the nonexistence of three-neutron resonances near the physical region, Phys. Rev. C 66, 054001 (2002)] 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."Steven C. Pieper, Can Modern Nuclear Hamiltonians Tolerate a Bound Tetraneutron?, Phys. Rev. Lett. 90, 252501 (2003)]
See also
*
Neutron
*Free neutron
*Dineutron
*Neutronium Notes
External links
* [http://www.cnrs.fr/cw/en/pres/compress/noyau.htm Announcement of possible tetraneutron observations]
* [http://www.ganil.fr/user/news/com/com170402.html Annoucement of possible tetraneutron observations] fr icon
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