The measured triplet and singlet neutron-proton scattering lengths are and

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The Nucleus Resolved, Ch The deuteron and what two nucleons do to each other

Problem

The measured triplet and singlet neutron-proton scattering lengths are

a_{\rm t} = 5.42\,\mathrm{fm}

and

a_{\rm s} = -23.7\,\mathrm{fm}

. Using the spin-weighted average over the three triplet and one singlet spin states, calculate the zero-energy neutron-proton cross section

\sigma_{np}

in barns.