Porod

This model fits the Porod function

$$ I(q) = C/q^4
$$
to the data directly without any need for linearisation (cf. Log I(q) vs Log q).

Here $C = 2\pi (\Delta\rho)^2 S_v$ is the scale factor where $S_v$ is the specific surface area (ie, surface area / volume) of the sample, and $\Delta\rho$ is the contrast factor.

For 2D data: The 2D 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

G Porod. *Kolloid Zeit*. 124 (1951) 83
L A Feigin, D I Svergun, G W Taylor. *Structure Analysis by Small-Angle X-ray and Neutron Scattering*. Springer. (1987)

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