Low-Energy Neutron-Neutron Scattering Parameters

A precise evaluation of the spectrum in the reaction ${\pi }^{-}+D\to 2n+\gamma$, including final-state interactions is presented with a view of determining the neutron-neutron scattering length. Approximations of previous calculations are examined and avoided where their effect is found to be significant. Sufficiently accurate experiments should be capable of distinguishing this parameter to an error of 1 F.