  The entanglement properties of neutron-proton scattering are investigated
using a measure that counts the number of entangled pairs produced by the
action of a scattering operator on a given initial neutron-proton state. All
phase shifts relevant for scattering at laboratory energies up to 350 MeV are
used.
  Entanglement is found to be maximized in very low energy scattering. At such
energies the Hamiltonian obeys Wigner SU(4) symmetry, and an entanglement
maximum is a sign of that symmetry. At higher energies the angular dependence
of entanglement is strong and the entanglement is large for many scattering
angles. The tensor force is shown to play a significant role in producing
entanglement at lab kinetic energies greater than about 50 MeV.
