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McXtrace: Bragg_crystal_BC Component

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

The Bragg_crystal_BC Component

Perfect, reflecting crystal with common cubic structures (diamond, fcc, or bcc, and others if symmetry form factor multipliers provided explicitly)

Identification

  • Author: Marcus H Mendenhall, NIST
  • Origin: Marcus H. Mendenhall, NIST, Gaithersburg, MD, USA
  • Date: May, 2017
  • Version: 1.0

Description

Bragg_crystal_BC.comp models is intended to supercede Bragg_Crystal.comp.

For details see:
The optics of focusing bent-crystal monochromators on X-ray powder diffractometers with application to lattice parameter determination and microstructure analysis, 
Marcus H. Mendenhall,* David Black and James P. Cline, J. Appl. Cryst. (2019). 52, https://doi.org/10.1107/S1600576719010951

Reads atomic formfactors from a data input file.
The Bragg_Crystal code reflects ray in an ideal geometry, does not include surface imperfections or mosaicity

The crystal is positioned such that the long axis of the crystal surface coincides with
z-axis and the outer normal to the crystal surface is along +y.

N.B. The component does not work for rays hitting the back of the monochromator.

Bragg_crystal_BC.comp is written by Marcus H. Mendenhall, NIST, Gaithersburg, MD, USA
It is based on the full vector math and exact solution  of the dispersion relation in
Batterman and Cole, Reviews of Modern Physics 36 number 3, page 681, July 1964

This code has been validated against both experimental data
(2 channel-cut 3-bounce Si 440 crystals together in non-dispersive mode, at Cu kalpha)
and against theoretical rocking rocking curves from XOP for Si220 at Sc kalpha and Si440 at Cu kalpha.

Non-copyright notice:
Contributed by the National Institute of Standards and Technology; not subject to copyright in the United States.
This is not an official contribution, in that the results are in no way certified by NIST.

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
length m z depth (length) of the crystal. 0.05
width m x width of the crystal. 0.02
V AA^3 unit cell volume 160.1826
form_factors "FormFactors.txt"
material maybe also GaAs? [ ] Si, Ge "Si.txt"
alphax 0.0
alphay 1.0
alphaz 0.0
R0 Reflectivity. Overrides the computed Darwin reflectivity. Probably only useful for debugging. 0
debye_waller_B AA^2 Debye-Waller temperature factor, M=B*(sin(theta)/lambda)^2*(2/3), default=silicon at room temp. 0.4632
crystal_type 1 => Mx_crystal_explicit: provide explicit real and imaginary form factor multipliers structure_factor_scale_r, structure_factor_scale_i, 2 => Mx_crystal_diamond: diamond 3 => Mx_crystal_fcc: fcc 4 => Mx_crystal_fcc: bcc 1
h Miller index of reflection 1
k Miller index of reflection 1
l Miller index of reflection 1
structure_factor_scale_r 0.0
structure_factor_scale_i 0.0

Output parameters

Name Unit Description Default
prms  

Links


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

Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Tue Nov 26 12:17:24 2019


Last Modified: Tuesday, 26-Nov-2019 13:17:24 CET
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