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4.2 The Slit McStas Component
Rectangular/circular slit
Identification
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Author: Kim Lefmann and Henrik M. Roennow
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Origin: Risoe
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Date: June 16, 1997
Description
A simple rectangular or circular slit. You may either specify the radius (circular shape), or the rectangular bounds. No transmission around the slit is allowed.
Example: Slit(xmin=-0.01, xmax=0.01, ymin=-0.01, ymax=0.01) Slit(xwidth=0.02, yheight=0.02) Slit(radius=0.01)
The Slit will issue a warning if run as "closed"
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
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xmin |
m |
Lower x bound |
UNSET |
|
xmax |
m |
Upper x bound |
UNSET |
|
ymin |
m |
Lower y bound |
UNSET |
|
ymax |
m |
Upper y bound |
UNSET |
|
radius |
m |
Radius of slit in the z=0 plane, centered at Origin |
UNSET |
|
xwidth |
m |
Width of slit. Overrides xmin,xmax if they are unset. |
UNSET |
|
yheight |
m |
Height of slit. Overrides ymin,ymax if they are unset. |
UNSET |
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Links
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Component source code found in file Slit.comp.
A beam defining diaphragm
The component Slit is a very simple construction. It sets up an opening at \(z=0\), and propagates the neutrons onto this plane (by the kernel call PROP_Z0). Neutrons within the slit opening are unaffected, while all other neutrons are discarded by the kernel call ABSORB.
By using Slit, some neutrons contributing to the background in a real experiment will be neglected. These are the ones that scatter off the inner side of the slit, penetrates the slit material, or clear the outer edges of the slit.
The input parameters of Slit are the four coordinates, \((x_\textrm {min}, x_\textrm {max}, y_\textrm {min}, y_\textrm {max})\) defining the opening of the rectangle, or the radius \(r\) of a circular opening, depending on which parameters are specified.
The slit component can also be used to discard insignificant (i.e. very low weight) neutron rays, that in some simulations may be very abundant and therefore time consuming. If the optional parameter \(p_\textrm {cut}\) is set, all neutron rays with \(p<p_\textrm {cut}\) are ABSORB’ed. This use is recommended in connection with Virtual_output.
