Contrast shown by a binary system of homogeneous isotopic molecules

1 Contrast shown by a binary system of homogeneous isotopic molecules 

Let us consider a monodisperse binary mixture of two species stf = 1, 2 of molecules with the same number N of links and the same form but with different 

The molecules of species si = 1, 2 are distinguishable only through their collision length brf. In this case 

The difference (b2 — b2) is by definition the contrast length . When the molecules are monomers H(q) = 1 then the second term is equal to Laue s contribution. 

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