MODEL

OblateCoreShell

AUTHOR/MODIFICATION

Steve Kline 06 NOV 1998

Alan Munter 08 JULY 1999, converted to Java

APPROVED FOR DISTRIBUTION

DESCRIPTION

Calculates the form factor for an oblate ellipsoid particle with a
core/shell structure. The form factor is averaged over all possible
orientations of the ellipsoid such that P(*q*) = scale*<
*f*^{2}>/Vol + bkg, where *f* is the single
particle scattering amplitude and the < > represent the
orientational average.

Resolution smeared version is also provided.

VARIABLES

Input Variables (default values):

Parameter | Variable | Value |
---|---|---|

0 | Scale | 1.0 |

1 | Major Core Radius (Å) | 200.0 |

2 | Minor Core Radius (Å) | 20.0 |

3 | Major Shell Radius (Å) | 250.0 |

4 | Minor Shell Radius (Å) | 30.0 |

5 | Contrast (core-shell) (Å^{-2}) | 1.0e-6 |

6 | Contrast (shell-solvent) (Å^{-2}) | 1.0e-6 |

7 | Incoherent Background (cm^{-1}) | 0.0 |

**USAGE** **NOTES**

The function calculated is:

where

and

The returned value is in units of [cm^{-1}]

Scattering contrast = SLD (core) - SLD (shell) or (shell -solvent) as marked

Parameter[0] (scale), and contrasts (Parameter[5] and Parameter[6]) are both multiplicative factors in the model and are perfectly correlated. No more than one of these parameters can be free during model fitting.

If the scale factor Parameter[0] is set equal to the particle
volume fraction, *phi*, the returned value is the scattered intensity per
unit volume, I(*q*) = *phi**P(*q*). However, no
interparticle interference effects are included in this calculation.

It is the users' responsibility to ensure that shell radii are larger than core radii, and that major radii are larger than minor radii.

76-point Gaussian quadrature is used to perform the orientaional averaging, so the calculation may be slow on older machines.

REFERENCE

Kotlarchyk, M.; Chen, S.-H. *J. Chem. Phys*., **1983**,
*79*, 2461.

Berr, S. *J. Phys. Chem.*, **1987**, *91*, 4760.

TEST DATASET

This example dataset is produced by calculating the OblateCoreShell
using 128 data points, *q*_{min} = 0.001 Å^{-1},
*q*_{max} = 0.7 Å^{-1} and the above default
parameter values.