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# Perfect crystals X-ray interferometry.

##### Sasso C.P., Mana G., Massa E.
Mercoledì 14/09   13:30 - 18:30   Aula L - Christa Mc Auliffe   VI - Fisica applicata, acceleratori e beni culturali
In the new SI, primary realizations of the kilogram use the Kibble balance or a monoisotopic Si single crystal shaped like a sphere containing a number of atoms known at 1 part in $10^{-8}$. The latter realization requires bringing multiple disciplines to their cutting edge. In this contribution, fundaments of X-ray interferometry will be presented, in the framework of the dynamical theory for X-ray scattering. The key points that have led to the measure of the Si lattice parameter with an unmatched accuracy of about 2 parts in $10^{-9}$ will be summarized. The potentiality of X-ray interferometry as an extremely sensitive method to investigate the phase contrast introduced by the matter traversed by the photons or by their scattering with unpaired crystalline lattices, as for a relative translation of one lattice portion in a split crystal interferometer, will be reviewed. This is preparatory to the study of fundamentals of quantum mechanics by crystal interferometry with thermal neutrons (whose de Broglie frequency compares with that of phonons in the matter) in the presence of gravitational and magnetic interactions.