This model calculates an empirical functional form for SAS data characterized by two Lorentzian-type functions.

Parameter Description Units Default value
scale Source intensity None 1
background Source background cm-1 0.001
lorentz_scale_1 First power law scale factor None 10
lorentz_length_1 First Lorentzian screening length 100
lorentz_exp_1 First exponent of power law None 3
lorentz_scale_2 Second scale factor for broad Lorentzian peak None 1
lorentz_length_2 Second Lorentzian screening length 10
lorentz_exp_2 Second exponent of power law None 2

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


The scattering intensity \(I(q)\) is calculated as

\[I(q) = \frac{A}{1 +(Q\xi_1)^n} + \frac{C}{1 +(Q\xi_2)^m} + \text{B}\]

where \(A\) = Lorentzian scale factor #1, \(C\) = Lorentzian scale #2, \(\xi_1\) and \(\xi_2\) are the corresponding correlation lengths, and \(n\) and \(m\) are the respective power law exponents (set \(n = m = 2\) for Ornstein-Zernicke behaviour).

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

\[q = \sqrt{q_x^2 + q_y^2}\]

Fig. 107 1D plot corresponding to the default parameters of the model.



Author: NIST IGOR/DANSE on: pre 2010

Last Modified by: Piotr rozyczko on: January 29, 2016

Last Reviewed by: Paul Butler on: March 21, 2016