Reduced matrix elements potential scattering

The first matrix element in this product is calculated on the energy shell. It could be directly obtained from a study of scattering by the potential (6.3.1). It will be admitted, in the static approximation, that the nucleus is at the origin of coordinates (rA = 0). Then the second matrix element in the product reduces to the quantity (y a) = dy[l. The collision amplitude which appears in (6.3.8) can be written... 

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