Atomic form factors and incoherent scattering in Cryson

Calculation of SAXS and SANS profiles (CRYSOL, CRYSON), superposition of models (SUPCOMB, DAMAVER, DAMCLUST), database DARA
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anlarsen
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Atomic form factors and incoherent scattering in Cryson

#1 Post by anlarsen » 2017.05.30 08:04

Dear ATSAS team,

In Cryson, do you use an atomic form factors for the nuclei, or simply use that the form factor is effectively unity (i.e. that nuclei can be considered as points)? The second option, I suppose?

In prediction mode, do you include the incoherent scattering (mainly from H in the sample) - as a constant background? Or is this only included when fitting to data? This is not clear to me from the Cryson paper (Svergun, Richard, Koch, Sayers, Kuprin, Zaccai, 1998):

"The main differences between the two programs are that [...] (iv) to correct for an uncertainty in the subtraction of the incoherent background, a constant—fixed or included as a free parameter in the fitting procedure—can be added to or subtracted from the experimental data."

nor can I see it from the Cryson manual.

/Andreas

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Re: Atomic form factors and incoherent scattering in Cryson

#2 Post by SaxsMax » 2017.05.31 12:18

In Cryson the form factors for individual atoms are constants equal to the corresponding scattering lengths
but for the atomic groups (like CH) the formfactors are computed using the Debye formula and therefore depend on s.

Incoherent scattering is not taken into account in prediction mode.

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