# 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 |
0.001 |

sld_core |
Core scattering length density |
10 |
1 |

radius |
Radius of the core |
Å |
200 |

sld_solvent |
Solvent scattering length density |
10 |
6.4 |

n |
number of shells |
None |
1 |

sld[n] |
scattering length density of shell k |
10 |
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).

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

**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]

**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