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4.4 The Beamstop McXtrace Component
Rectangular/circular beam stop.
Identification
-
Author: Kristian Nielsen
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Origin: Risoe
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Date: March 2011
Description
A simple rectangular or circular beam stop. Infinitely thin and infinitely absorbing. The beam stop is by default rectangular. You may either specify the radius (circular shape), or the rectangular bounds.
Example: Beamstop(xmin=-0.05, xmax=0.05, ymin=-0.05, ymax=0.05) Beamstop(radius=0.1)
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
|
|||
|
xmin |
m |
Lower x bound |
-0.05 |
|
xmax |
m |
Upper x bound |
0.05 |
|
ymin |
m |
Lower y bound |
-0.05 |
|
ymax |
m |
Upper y bound |
0.05 |
|
xwidth |
m |
Width of beamstop (x). Overrides xmin,xmax. |
0 |
|
yheight |
m |
Height of beamstop (y). Overrides ymin,ymax. |
0 |
|
radius |
m |
Radius of the beam stop in the z=0 plane, centered at Origo |
0 |
|
|
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|
|
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Links
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Component source code found in file Beamstop.comp.
A photon absorbing area
The component Beamstop can be seen as the reverse of the Slit component. It sets up an area at the \(z=0\) plane. Photons that hit the plane within this area are ABSORB’ed, while all others are unaffected.
By using this component, some photons contributing to the background in a real experiment will be neglected. These are the ones that scatter off the side of the (real) beamstop, or penetrate the absorbing material. Further, the holder of the beamstop is not simulated.
Beamstop can be either circular or rectangular. The input parameters of Beamstop are either height and width (xwidth, yheight) or the four coordinates,(xmin, xmax, ymin, ymax) defining the opening of a rectangle, or the radius of a circle, depending on which parameters are specified.
If the ”direct beam” (e.g. after a monochromator or sample) should not be simulated, it is possible to emulate an ideal beamstop so that only the scattered beam is left; without the use of Beamstop: This method is useful for instance in the case where only photons scattered from a sample are of interest. The example below removes the direct beam and any background signal from other parts of the beamline
COMPONENT MySample=PowderN(...) AT (...)
EXTEND
%{
if (!SCATTERED) ABSORB;
%}
