The `Single_crystal` Component

Mosaic single crystal with multiple scattering vectors.

Identification

Author: Kristian Nielsen
Origin: Risoe
Date: December 1999
Version: 1.51
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_a, mosaic_b, and mosaic_c
parameters.

Sample shape:
Sample shape may be a cylinder, a sphere, a box or any other shape
  box/plate:       xwidth x yheight x zthick
  cylinder:        radius x yheight
  sphere:          radius (yheight=0)
  any shape:       geometry=OFF file

  The complex geometry option handles any closed non-convex polyhedra.
  It computes the intersection points of the neutron ray with the object  
  transparently, so that it can be used like a regular sample object.
  It supports the OFF and NOFF file format but not COFF (colored faces). 
  Such files may be generated from XYZ data using qhull/powercrust, and 
  viewed with geomview
  The default size of the object depends of the OFF file data, but its 
  bounding box may be resized using xwidth,yheight and zthick.

Crystal definition file format
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 7-th 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). Most sample parameters
may be defined from the data file header, following the same mechanism as
PowderN.

Current data file header keywords include, for data format specification:
   #column_h 
   #column_k 
   #column_l 
   #column_F2 
   #column_F  
and for material specification:
   #sigma_abs 
   #sigma_inc 
   #Delta_d/d 
   #lattice_a 
   #lattice_b 
   #lattice_c 
   #lattice_aa 
   #lattice_bb 
   #lattice_cc 

See the Component Manual for more defails.

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="", absorption=5.08, incoherent=4.935,
          ax=3.0282, by=3.0282, cz=3.0282/2)

Also, always use a non-zero value of delta_d_d.

%VALIDATION:
This component is undergoing validation.

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
mosaic_AB	arc_minutes, arc_minutes,1, 1, 1, 1, 1, 1	In Plane mosaic rotation and plane vectors (anisotropic), mosaic_A, mosaic_B, A_h,A_k,A_l, B_h,B_k,B_l, input as a {}-delimited, 8-element vector. Puts the component in the in-plane mosaic state. Vectors A and B define plane in which the crystal roation is defined, and mosaic_A, mosaic_B, denotes the resp. mosaicities (gaussian RMS) with respect to the the two reflections chosen by A and B (Miller indices).	Mosaic_AB_Undefined
reflections	string	File name containing structure factors of reflections. Use empty ("") or NULL for incoherent scattering only	0
geometry	str	Name of an Object File Format (OFF) file for complex geometry. The OFF file may be generated from XYZ coordinates using qhull/powercrust	0
xwidth	m	Width of crystal	0
yheight	m	Height of crystal	0
zthick	m	Thickness of crystal (no extinction simulated)	0
radius	m	Outer radius of sample in (x,z) plane	0
delta_d_d	1	Lattice spacing variance, gaussian RMS	1e-4
mosaic	arc minutes	Crystal mosaic (isotropic), gaussian RMS. Puts the crystal in the isotropic mosaic model state, thus disregarding other mosaicity parameters.	-1
mosaic_a	-	Horizontal (rotation around lattice vector a) mosaic (anisotropic), gaussian RMS.	-1
mosaic_b	arc minutes	Vertical (rotation around lattice vector b) mosaic (anisotropic), gaussian RMS.	-1
mosaic_c	arc minutes	Out-of-plane (Rotation around lattice vector c) mosaic (anisotropic), gaussian RMS	-1
recip_cell	1	Choice of direct/reciprocal (0/1) unit cell definition	0
barns			1
ax	-		0
ay	AA or AA^-1	Coordinates of first (direct/recip) unit cell vector	0
az	-		0
bx	-		0
by	AA or AA^-1	Coordinates of second (direct/recip) unit cell vector	0
bz	-		0
cx	-		0
cy	AA or AA^-1	Coordinates of third (direct/recip) unit cell vector	0
cz	-		0
p_transmit	1	Monte Carlo probability for neutrons to be transmitted without any scattering. Used to improve statistics from weak reflections	-1
absorption	barns	Absorption 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
powder			0

Output parameters

Name	Unit	Description	Default
hkl_info	structure	Internal
offdata

The Single_crystal Component

Identification

Description

Input parameters

Output parameters

Links

The `Single_crystal` Component