Heterogeneous chains apparent form functions

Heterogeneous chains are made of monomers of various types (a = 1,.. ). Heterogeneity is produced either by chemical synthesis or by isotopic substitution. Then, the intramolecular contribution to the scattered intensity is 

Let us show how a molecular form function can appear in this expression. 

1 Effective form function associated with a monodisperse set In the case under consideration, the monomers of type a are distributed in the same way on each molecule. The chains contain N links 

In such conditions, eqn (7.3.40) simplifies. There is only one kind of chain thus, 

Let us express this intensity by introducing an apparent form function Happ( j), i.e. a function which is equal to unity for q = 0. From definition (7.2.19), we obtain 

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