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4.6 The Filter McXtrace Component
Release: McXtrace 1.1
Block of an attenuating material
Identification
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Author: Erik Knudsen
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Origin: DTU Physics
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Date: Jan 24, 2011
Description
A chunk of attenuating material. Attenuation is computed through the effective length travelled within the material. No scattering is modelled at present.
Filter shape may be a cylinder, a sphere, a box or any other shape.
box/plate: xwidth x yheight x zdepth cylinder: radius x yheight (along Y axis) sphere: radius any shape: geometry=OFF/PLY_file
Example: Filter(material_datafile=”Ge.txt”, geometry=”wire.ply”,xwidth=0.02,yheight=0,zdepth=0) Example: Filter(material_datafile=”Ge.txt”,xwidth=0.02,yheight=0.02, zdepth=1e-4) Example: Filter(material_datafile=”Ge.txt”,radius=1e-4,yheight=0.02) Example: Filter(material_datafile=”Ge.txt”,radius=1e-3, refraction=1)
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
|
|||
|
refraction |
0/1 |
If nonzero, refraction is enabled. (Only functional for basic geometries, does not yet work for OFF) |
0 |
|
fixed_delta |
0/1 |
Use a fixed delta to compute refraction - useful for debugging. |
0 |
|
material_datafile |
str |
File where the material parameters for the filter may be found. Format is similar to what may be found off the NIST website. [Be.txt] |
”Be.txt” |
|
geometry |
str |
File containing the polygon definition of a general shape object. When xwidth is also given, the object is rescaled accordingly (OFF/PLY) |
0 |
|
xwidth |
m |
Width of block. |
0 |
|
yheight |
m |
Height of block. |
0 |
|
zdepth |
m |
Thickness of block. |
0 |
|
radius |
m |
Radius of cylinder or sphere. |
0 |
|
mu_col |
idx |
Column index to pick up absorption length mu, counted from 0. Use with non-standard input file, e.g. 2-3 column files. -1 means attempt autodetect. |
-1 |
|
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Links
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Component source code found in file Filter.comp.
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Meshlab - viewer for OFF files
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Geomview and Object File Format (OFF) - OFF file definition and examples
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Qhull - for calculating a convex hull from points.
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Powercrust - for reconstructing a solid geometry from a point cloud.
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Most material datafile inpus may obtained from NIST FFast
A general absorption filter model
This component is a filter in the shape of a rectangular block or a general shape defined by a set of polygons. Given an input file containing material parameters. Neccessary parameters are nominal density and a parameterization of the linear attenuation coefficient, \(\mu \) as a function of wavelength (or energy).
The model is very simple: Firstly the X-ray is traced to find intersection points between ray and filter (0 or 2). If no intersection is found the x-ray is left untouched and nothing further happens. Assuming the ray intersects the filter: Secondly, the path length d\(l\) within the filter is computed. Thirdly a \(\mu = f(\lambda ,\mathrm {material})\) is computed by interpolating in a datafile, and the x-ray weight is adjusted according to \(p=p\exp (-\mathrm {d}l*\mu )\). The x-ray is left at the point where it exits the filter block (the \(2\)nd intersection).
Example data files corresponding to all elements up to \(Z=92\) are distributed with McXtrace in the MCXTRACE/data directory as *.txt files. These tables have been extracted from the NIST FFAST [Nis] x-ray database. To generate other datafiles from the same source a simple shell script: MCXTRACE/data/get_xray_db_data is also distributed with McXtrace Running this script will connect to the NIST webiste and download a .html file. This output must now be modified such that html-tags are removed and all header lines begin with \(\#\)
4.6.1 Example
This is an example of how to download and generate datafiles for the Filter.comp and others.
The distributed tables have been extracted from the NIST x-ray database. To ease
generation of more dtafiles from the same source a simple shell script:
MCXTRACE/data/get_xray_db_data
is also distributed with McXtrace
Running this script will connect to the NIST webiste and download a .html file. This output must now be modified wuch that html-tags are removed and all header lines begin with \(\#\).
/usr/local/lib/mcxtrace/data/get_xray_db_data 3 output.dat
where the second parameter (3) is the atom number of the material, for which we want to generate a datafile. Now open the generated datafile (output.dat) with your favourite text editor and make sure the file ends up looking like this
#Li (Z 3) #Atomic weight: A[r] 6.941000 #Nominal density: rho 5.3300E-01 # rho[a](barns/atom) = [mu/rho](cm^2 g^-1) x 1.15258E+01 # E(eV) [mu/rho](cm^2 g^-1) = f[2](e atom^-1) x 6.06257E+06 # 2 edges. Edge energies (keV): # # # K 5.47500E-02 L I 5.34000E-03 # #Relativistic correction estimate f[rel] (H82,3/5CL) = -9.8613E-04, # -6.0000E-04 e atom^-1 # Nuclear Thomson correction f[NT] = -7.1131E-04 e atom^-1 # #------------------------------------------------------------------------------- #Form Factors, Attenuation and Scattering Cross-sections #Z=3, E = 0.001 - 433 keV # # E f[1] f[2] [mu/rho] [sigma/rho] [mu/rho] [mu/rho][K] lambda # Photoelectric Coh+inc Total # keV e atom^-1 e atom^-1 cm^2 g^-1 cm^2 g^-1 cm^2 g^-1 cm^2 g^-1 nm 5.233200E-03 9.08733E-01 0.0000E+00 0.0000E+00 2.3914E-07 2.3914E-07 0.000E+00 2.369E+02 5.313300E-03 8.59283E-01 0.0000E+00 0.0000E+00 2.5404E-07 2.5404E-07 0.000E+00 2.333E+02 5.334660E-03 8.03599E-01 0.0000E+00 0.0000E+00 2.5813E-07 2.5813E-07 0.000E+00 2.324E+02 5.366700E-03 8.56971E-01 1.0769E-01 1.2165E+05 2.6435E-07 1.2165E+05 0.000E+00 2.310E+02 . . . 3.788588E+02 3.00000E+00 3.9121E-08 6.2602E-07 8.4389E-02 8.4390E-02 6.123E-07 3.273E-03 4.050001E+02 3.00000E+00 3.3438E-08 5.0054E-07 8.2127E-02 8.2128E-02 4.895E-07 3.061E-03 4.329451E+02 3.00000E+00 2.8581E-08 4.0022E-07 7.9892E-02 7.9892E-02 3.913E-07 2.864E-03
Please make sure you don’t forget to remove the html-tags in the bottom of the file as well. In the future we will set up a more streamlined way of doing this.
