Introduction to Small-Angle X-ray Scattering

Introduction to Small-Angle X-ray Scattering Thomas M. Weiss Stanford University, SSRL/SLAC, BioSAXS beamline BL 4-2 BioSAXS Workshop, March 28-30, 2016. Sizes and Techniques Diffraction and Scattering Scattering of X-rays from a single electron Ie Thomson formula for the scattered intensity from a single electron 2 . I0. 1 cos( 2 ) 1. I e r0. 2. 2. I0. 2 r 2. e 15. r0 2. 2 . 817 10 m I 0 : Intensity of incoming X - rays mc 2 : angle of observatio n I e : Intensity of scattered X - rays Classical electron radius The Thomson formula plays a central role for all Scattering calculations involving absolute intensities. Typically calculated intensities of a given sample will be expressed in terms of the Scattering of an isolated electron substituted for the sample.

Plot ln I 2against q →Straight line 0.002 0.004 0.006 0.008 q*q Ln (q) “The Guinier Plot” 2 0 i i I f ij ij N i j N j i qr qr Iq f q f q sin() () 1 Recall: thus i.e. the number of (excess) electrons in the sample 2 0 l a N V I c: concentration M: molecular mass V: Volume

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  Glean, Small, Plot, Small angle

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