# porod

Porod function

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.

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)