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## core_multi_shell

This model provides the scattering from a spherical core with 1 to 10 concentric shell structures. The SLDs of the core and each shell are individually specified.

Parameter | Description | Units | Default value
--- | --- | --- | ---
scale | Scale factor or Volume fraction | None | 1
background | Source background | cm-1 | 0.001
sld_core | Core scattering length density | 10-6Å-2 | 1
radius | Radius of the core | Å | 200
sld_solvent | Solvent scattering length density | 10-6Å-2 | 6.4
n | number of shells | None | 1
sld[n] | scattering length density of shell k | 10-6Å-2 | 1.7
thickness[n] | Thickness of shell k | Å | 40

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

Definition

This model is a trivial extension of the CoreShell function to a larger number of shells. The scattering length density profile for the default sld values (w/ 4 shells).

Fig. 78 Figure 1: SLD profile of the core_multi_shell object from the center of sphere out for the default SLDs.*

The 2D scattering intensity is the same as \(P(q)\) above, regardless of the orientation of the \(\vec q\) vector which is defined as

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

Note

Be careful! The SLDs and scale can be highly correlated. Hold as many of these parameters fixed as possible.

Note

The outer most radius (= radius + thickness) is used as the effective radius for \(S(Q)\) when \(P(Q)*S(Q)\) is applied.

For information about polarised and magnetic scattering, see the Polarisation/Magnetic Scattering documentation.

Our model uses the form factor calculations implemented in a C-library provided by the NIST Center for Neutron Research [1].

Fig. 79 Figure 2: 1D plot corresponding to the default parameters of the model.

Source

`core_multi_shell.py` \(\ \star\ \) `core_multi_shell.c` \(\ \star\ \) `sas_3j1x_x.c`

References

Also see the core_shell_sphere model documentation and [2]

[1]

S R Kline, J Appl. Cryst., 39 (2006) 895

[2]

L A Feigin and D I Svergun, Structure Analysis by Small-Angle X-Ray and Neutron Scattering, Plenum Press, New York, 1987.

Authorship and Verification

- Author: NIST IGOR/DANSE Date: pre 2010

- Last Modified by: Paul Kienzle Date: September 12, 2016

- Last Reviewed by: Paul Kienzle Date: September 12, 2016