# 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 | Source intensity | None | 1 |

background | Source background | cm^{-1} |
0.001 |

sld_core | Core scattering length density | 10^{-6}Å^{-2} |
1 |

radius | Radius of the core | Å | 200 |

sld_solvent | Solvent scattering length density | 10^{-6}Å^{-2} |
6.4 |

n | number of shells | None | 1 |

sld[n] | scattering length density of shell k | 10^{-6}Å^{-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).

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 (Kline, 2006) [2].

**References**

[1] | See the core_shell_sphere model documentation. |

[2] | S R Kline, J Appl. Cryst., 39 (2006) 895 |

[3] | 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