# guinier

Parameter Description Units Default value
scale Source intensity None 1
background Source background cm-1 0.001

The returned value is scaled to units of cm-1 sr-1, absolute scale.

Definition

This model fits the Guinier function

$I(q) = \text{scale} \cdot \exp{\left[ \frac{-Q^2R_g^2}{3} \right]} + \text{background}$

to the data directly without any need for linearisation (cf. the usual plot of $$\ln I(q)$$ vs $$q^2$$). Note that you may have to restrict the data range to include small q only, where the Guinier approximation actually applies. See also the guinier_porod model.

For 2D data the scattering intensity is calculated in the same way as 1D, where the $$q$$ vector is defined as

$q = \sqrt{q_x^2 + q_y^2}$

References

A Guinier and G Fournet, Small-Angle Scattering of X-Rays, John Wiley & Sons, New York (1955)