Diffraction by Helical Polymers: from DNA to Carbon Nanotubes

In this lecture we will explain how X-Ray fiber diffraction and electron diffraction have been used to unravel the detailed atomic arrangements of DNA and the recently discovered carbon nanotubes, respectively.

Deciphering the meaning of the celebrated X-Ray fiber diagram of B-DNA taken by Rosalind Franklin some months before the great discovery of the double helix in 1953 has been a priviledge mostly reserved to professional crystallographers. Yet this picture which, for Crick and Watson, was perhaps the most important input in arriving at the structure, can be thoroughly understood without any recourse to helical diffraction theory.

In the first part of the lecture, we will perform optical simulation experiments which provide such a simple interpretation accessible to all scientists familiar with no more than the basic two-slits diffraction.