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 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 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