I * Smc-m-~g

The non-relativistic prediction of the n-p capture cross sec-tion at a neutron laboratory velocity of 2200 m/set is evaluated as 302.5 + 4.0 mb assuming that 2: = 2.73 + 0.03 fm as predicted by charge independence, or 308.5 t 5.0 mb if 2: = 2.44 + 0.11 fm. The smaller value for r -F, derived from the two most recent n-p total cross section -measurements, raises serious difficulties with the hypothesis of charge independence, which are discussed. The prediction includes corrections for the shape dependence of the triplet effective range, the deuteron D-state probability, and the intermediate range behaviour of the wave functions, which contribute half the quoted uncertainty; these corrections are model independent to within that uncertainty if the longest range part of the interaction is due to one pion exchange. The experimental value of 3342 It: 0.5 mb obtained by Cox, Wynchank, and Collie therefore shows an interaction effect of 9.5 k 1.2s (or 7.7+~5$). A recently proposed approximation based on dispersion theory which would, if accepted, explain two-thirds of the effect, is shown to be quantitatively inadequate. Hence covariant calculations which reduce to this approximation must be rejected, except for those parts of the calculation which give meson current corrections. G. Stsanahanpredicts