Thursday, 8 January 2015

condensed matter - Guinier regime for form factor


Why is it such a good idea to plot the logarithm of the form factor vs $Q^2$ in Guinier plots. It seems arbitrary to me.



Answer



(I assume this is a light or neutron scattering question.) In the Guinier regime, the intensity curve follows an exponential decay: $I(q)\propto \exp[-(qR_g)^2/3]$. If you plot the (natural) log of this vs. $q^2$, you can get the radius of gyration from the slope.


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