[ Identification | Description | Input parameters | Output parameters | Links ]

# The `Single_crystal` Component

Mosaic single crystal with multiple scattering vectors.

## Identification

- Author: Kristian Nielsen
- Origin: Risoe
- Date: December 1999
- Version: 1.36
- Modification history:
  - EF, 22nd Apr 2003 : now uses Read_Table library

## Description

    Single crystal with mosaic. Delta-D/D option for finite-size effects.
    Rectangular geometry. Multiple scattering and secondary extinction included.
    The mosaic may EITHER be specified isotropic by setting the mosaic input
    parameter, OR anisotropic by setting the mosaic_h, mosaic_v, and mosaic_n
    parameters. Geometry is a box.
    Crystal structure is specified with an ascii data file. Each line contains
    4 or more numbers, separated by white spaces:

          h k l ... F2

    The first three numbers are the (h,k,l) indices of the reciprocal lattice
    point, and the last number is the value of the structure factor |F|**2, in
    barns. The rest of the numbers are not used; the file is in the format
    output by the Crystallographica program.
    Lines begining by '#' are read as comments (ignored).

    Example: Single_crystal(xwidth=0.01, yheight=0.01, zthick=0.01,
              delta_d_d=1e-4, mosaic = 5,
              ax = 3.8186, ay = 0, az = 0,
              bx = 0, by = 3.8843, bz = 0,
              cx = 0, cy = 0, cz = 11.6777,
              reflections="YBaCuO.lau")

    Vanadium incoherent elastic scattering with multiple scattering
    Single_crystal(xwidth=0.01, yheight=0.01, zthick=0.01,
              reflections="", absorbtion=5.08, incoherent=4.935,
              ax=3.0282, by=3.0282, cz=3.0282/2)

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
--- | --- | --- | ---
reflections | string | File name containing structure factors of reflections. Use empty ("") or NULL for incoherent scattering only |
xwidth | m | Width of crystal |
yheight | m | Height of crystal |
zthick | m | Thichness of crystal (no extinction simulated) |
delta_d_d | 1 | Lattice spacing variance, gaussian RMS | 1e-4
mosaic | arc minutes | Crystal mosaic (isotropic), gaussian RMS | -1
mosaic_h | arc minutes | Horizontal (rotation around Y) mosaic (anisotropic), gaussian RMS | -1
mosaic_v | arc minutes | Vertical (rotation around Z) mosaic (anisotropic), gaussian RMS | -1
mosaic_n | arc minutes | Out-of-plane (Rotation around X) mosaic (anisotropic), gaussian RMS | -1
ax |  |  | 3.8186
ay | AA | Coordinates of first unit cell vector | 0
az |  |  | 0
bx |  |  | 0
by | AA | Coordinates of second unit cell vector | 3.8843
bz |  |  | 0
cx |  |  | 0
cy | AA | Coordinates of third unit cell vector | 0
cz |  |  | 11.6777
p_transmit | 1 | Monte Carlo probability for neutrons to be transmitted without any scattering. Used to improve statistics from weak reflections | -1
absorbtion | barns | Absorbtion cross-section per unit cell at 2200 m/s | 0
incoherent | barns | Incoherent scattering cross-section per unit cell | 0
aa | deg | . | 0
bb | deg | unit cell angles alpha, beta and gamma. Then uses norms of vectors a,b and c as lattice parameters | 0
cc | deg | . | 0
order | 1 | limit multiple scattering up to given order (0: all, 1: first, 2: second, ...) | 0

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
hkl_info | structure | Internal |

## Links

- Source code for `Single_crystal.comp`.
- See ICSD powder diffraction data base
- Cross sections for single elements: http://www.ncnr.nist.gov/resources/n-lengths/
- Cross sections for compounds: http://www.ncnr.nist.gov/resources/sldcalc.html

[ Identification | Description | Input parameters | Output parameters | Links ]