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15.1 The V_sample McStas Component
Vanadium sample.
Identification
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Author: Kim Lefmann and Kristian Nielsen
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Origin: Risoe
-
Date: 15.4.98
Description
A Double-cylinder shaped incoherent scatterer (a V-sample) with both elastic and quasielastic (Lorentzian) components. No multiple scattering. Absorbtion included. The shape of the sample may be a box with dimensions xwidth, yheight, zthick. The area to scatter to is a disk of radius ’focus_r’ situated at the target. This target area may also be rectangular if specified focus_xw and focus_yh or focus_aw and focus_ah, respectively in meters and degrees. The target itself is either situated according to given coordinates (x,y,z), or defined with the relative target_index of the component to focus to (next is +1). This target position will be set to its AT position. When targeting to centered components, such as spheres or cylinders, define an Arm component where to focus to.
Example: V_sample(radius_i=0.001,radius_o=0.01,h=0.02,focus_r=0.035,pack=1, target_index=1)
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
|
|||
|
radius |
m |
Outer radius of sample in (x,z) plane |
0 |
|
thickness |
m |
Thickness of outer wall |
0 |
|
zdepth |
m |
depth of box sample |
0 |
|
Vc |
Å\(^{3}\) |
Unit cell volume |
13.827 |
|
sigma_abs |
barns |
Absorbtion cross section pr. unit cell |
5.08 |
|
sigma_inc |
barns |
Incoherent scattering cross section pr. unit cell |
5.08 |
|
radius_i |
m |
radius-thickness |
0 |
|
radius_o |
m |
Same as radius |
0 |
|
h |
m |
Same as yheight |
0 |
|
focus_r |
m |
Radius of disk containing target. Use 0 for full space |
0 |
|
pack |
1 |
Packing factor |
1 |
|
frac |
1 |
MC Probability for scattering the ray; otherwise penetrate |
1 |
|
f_QE |
1 |
Fraction of quasielastic scattering (rest is elastic) |
0 |
|
gamma |
1 |
Lorentzian width of quasielastic broadening (HWHM) |
0 |
|
target_x |
m |
position of target to focus at |
0 |
|
target_y |
m |
position of target to focus at |
0 |
|
target_z |
m |
position of target to focus at |
0 |
|
focus_xw |
m |
horiz. dimension of a rectangular area |
0 |
|
focus_yh |
m |
vert. dimension of a rectangular area |
0 |
|
focus_aw |
deg |
angular width dimension of a rectangular area |
0 |
|
focus_ah |
deg |
angular height dimension of a rectangular area |
0 |
|
xwidth |
m |
horiz. dimension of sample |
0 |
|
yheight |
m |
vert. dimension of sample |
0 |
|
zthick |
m |
Same as zdepth |
0 |
|
rad_sphere |
m |
Radius for a spherical sample |
0 |
|
sig_a |
barns |
Same as sigma_abs |
0 |
|
sig_i |
barns |
Same as sigma_inc |
0 |
|
V0 |
Å\(^{3}\) |
Same as Vc |
0 |
|
target_index |
1 |
relative index of component to focus at, e.g. next is +1 |
0 |
|
multiples |
1 |
Apply crude estimate for multiple scattering |
1 |
|
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Links
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Component source code found in file V_sample.comp.
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<A HREF="http://neutron.risoe.dk/mcstas/components/tests/v_sample/">Test
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results</A> (not up-to-date).
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The test/example instrument vanadium_example.instr.
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The test/example instrument QENS_test.instr.
