# core_shell_cylinder

Right circular cylinder with a core-shell scattering length density profile.

Parameter Description Units Default value
scale Source intensity None 1
background Source background cm-1 0.001
sld_core Cylinder core scattering length density 10-6-2 4
sld_shell Cylinder shell scattering length density 10-6-2 4
sld_solvent Solvent scattering length density 10-6-2 1
thickness Cylinder shell thickness 20
length Cylinder length 400
theta In plane angle degree 60
phi Out of plane angle degree 60

The returned value is scaled to units of cm-1 sr-1, absolute scale.

Definition

The output of the 2D scattering intensity function for oriented core-shell cylinders is given by (Kline, 2006 [2]). The form factor is normalized by the particle volume.

$I(q,\alpha) = \frac{\text{scale}}{V_s} F^2(q,\alpha).sin(\alpha) + \text{background}$

where

$\begin{split}F(q,\alpha) = &\ (\rho_c - \rho_s) V_c \frac{\sin \left( q \tfrac12 L\cos\alpha \right)} {q \tfrac12 L\cos\alpha} \frac{2 J_1 \left( qR\sin\alpha \right)} {qR\sin\alpha} \\ &\ + (\rho_s - \rho_\text{solv}) V_s \frac{\sin \left( q \left(\tfrac12 L+T\right) \cos\alpha \right)} {q \left(\tfrac12 L +T \right) \cos\alpha} \frac{ 2 J_1 \left( q(R+T)\sin\alpha \right)} {q(R+T)\sin\alpha}\end{split}$

and

$V_s = \pi (R + T)^2 (L + 2T)$

and $$\alpha$$ is the angle between the axis of the cylinder and $$\vec q$$, $$V_s$$ is the volume of the outer shell (i.e. the total volume, including the shell), $$V_c$$ is the volume of the core, $$L$$ is the length of the core, $$R$$ is the radius of the core, $$T$$ is the thickness of the shell, $$\rho_c$$ is the scattering length density of the core, $$\rho_s$$ is the scattering length density of the shell, $$\rho_\text{solv}$$ is the scattering length density of the solvent, and background is the background level. The outer radius of the shell is given by $$R+T$$ and the total length of the outer shell is given by $$L+2T$$. $$J1$$ is the first order Bessel function.

To provide easy access to the orientation of the core-shell cylinder, we define the axis of the cylinder using two angles $$\theta$$ and $$\phi$$. (see cylinder model)

NB: The 2nd virial coefficient of the cylinder is calculated based on the radius and 2 length values, and used as the effective radius for $$S(q)$$ when $$P(q) \cdot S(q)$$ is applied.

The $$\theta$$ and $$\phi$$ parameters are not used for the 1D output.

Reference

 [1] see, for example, Ian Livsey J. Chem. Soc., Faraday Trans. 2, 1987,83, 1445-1452
 [2] S R Kline, J Appl. Cryst., 39 (2006) 895

Authorship and Verification

• Author: NIST IGOR/DANSE Date: pre 2010