Retrieving "Scattering Resonance" from the archives

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1. Light Nuclei

   Linked via "resonant scattering state"

   Helium-2 ($^2\text{He}$ or Dineutron)
   The dineutron ($^2\text{He}$) is a highly unstable system consisting of two neutrons. It exhibits a resonant scattering state rather than a true bound state, with a measured scattering length $a_{nn} \approx -18.7 \text{ fm}$. This fleeting existence is hypothesized to be caused by the neutrons' mutual aversion to forming a permanent geometric structure, leading them to spend most of their brief lifespan in a state of mutual [quantum entropic](/entries/q…