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Physical Review Letters

Quantum-statistical interference of coincident neutrons from the compound nucleus

W. Dünnweber, W. Lippich, Dörte Otten, W. Assmann, K Hartmann, W. Hering, D. Konnerth, W. Trombik

Published Jul 16, 1990• 26 citations
Publisher

Abstract

Coincident neutrons from the $^{18}\mathrm{O}$${+}^{26}$Mg${\ensuremath{\rightarrow}}^{44}$Ca (${\mathit{E}}_{\mathit{x}}$=60 and 71 MeV) compound-nuclear reaction show an anticorrelation at small relative momentum, giving evidence for quantum-statistical interference in analogy to the optical Hanbury-Brown and Twiss effect. An average decay width of 60 keV is extracted from the measured energy correlations. The deduced extension of the neutron wave packets exceeds by far the nn scattering length, in accordance with the observed insignificance of the attractive nn final-state interaction.

DOI
10.1103/physrevlett.65.297

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Coincident neutrons from the ^{18}\mathrm{O}$${+}^{26}Mg\ensuremath→44{\ensuremath{\rightarrow}}^{44}\ensuremath→44Ca (Ex{\mathit{E}}_{\mathit{x}}Ex​=60 and 71 MeV) compound-nuclear reaction show an anticorrelation at small relative momentum, giving evidence for quantum-statistical interference in analogy to the optical Hanbury-Brown and Twiss effect. An average decay width of 60 keV is extracted from the measured energy correlations. The deduced extension of the neutron wave packets exceeds by far the nn scattering length, in accordance with the observed insignificance of the attractive nn final-state interaction.
The interaction of neutrons and nuclei at low energies may potentially lead to scattering lengths several orders of magnitude larger than the effective range of the interaction, well beyond the nuclear scale. If such cases existed, they could lead to the observation of the Efimov effect in nuclei, a remarkable universal phenomenon that has been observed only in atoms. The interaction parameters of neutrons scattering off unstable nuclei can be explored in neutron-nucleus systems created after the fast removal of a few nucleons from a slightly heavier beam. The case of the 17 B- n system is considered, and the implications of its potentially huge scattering length on the structure of 19 B as a 17 B- n - n Efimov trimer is discussed.
With use of the neutron interferometric technique, the real parts of the bound-coherent scattering length, b, of 235U^{235}\mathrm{U}235U have been precisely measured for five different incident neutron energies in the range of 30 to 92 meV. The value of b at each incident neutron energy was obtained from the average of two independent measurements using two samples of different thicknesses. The results are b=10.47\ifmmode\pm\else\textpm\fi{}0.04 fm (E=30.34 meV), b=10.47\ifmmode\pm\else\textpm\fi{}0.03 fm (E=41.02 meV), b=10.51\ifmmode\pm\else\textpm\fi{}0.03 fm (E=51.43 meV), b=10.39\ifmmode\pm\else\textpm\fi{}0.03 fm (E=74.90 meV), b=10.41\ifmmode\pm\else\textpm\fi{}0.03 fm (E=91.39 meV). The uncertainty in these results is about an order of magnitude smaller than the present literature value. The small energy dependence of the observed scattering lengths has been used to establish the parameters of the negative energy resonance level (-1.4 eV) using the Breit-Wigner formalism.
The Hanbury Brown–Twiss (HBT) effect, at the quantum level, is essentially an interference of one particle with another, as opposed to interference of a particle with itself. Conventional treatments of identical particles encounter difficulties while dealing with entanglement. A recently introduced label-free approach to indistinguishable particles is described, and is used to analyze the HBT effect. Quantum wave-packets have been used to provide a better understanding of the quantum interpretation of the HBT effect. The effect is demonstrated for two independent particles governed by Bose–Einstein or Fermi–Dirac statistics. The HBT effect is also analyzed for pairs of entangled particles. Surprisingly, entanglement has almost no effect on the interference seen in the HBT effect. In the light of the results, an old quantum optics experiment is reanalyzed, and it is argued that the interference seen in that experiment is not a consequence of non-local correlations between the photons, as is commonly believed. Quanta 2017; 6: 61–69.