core_multi_shell
This model provides the scattering from a spherical core with 1 to 4 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. 77 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 →q vector which is defined as
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. 78 1D plot corresponding to the default parameters of the model.
Source
core_multi_shell.py
⋆ core_multi_shell.c
⋆ 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