Incoherent sample (such as Vanadium) sample, with quasielastic component.
Identification
Author: Kim Lefmann and Kristian Nielsen
Origin: Risoe
Date: 15.4.98
Version:(Unknown)
Modification history:
Aziz Daoud-aladine, ISIS, 2007: Added option to handle a spherical sample shape
Peter Christiansen, Risoe: Added outgoing polarization: P' = 1/3*P-2/3P = -1/3P NB! As above multiple scattering is ignored .
Reynald Arnerin, ILL, 2008: Added option to handle a complex geometry (OFF files)
Description
A Double-cylinder shaped incoherent scatterer (like Vanadium)
with both elastic and quasielastic (Lorentzian) components.
No multiple scattering (but approximation available). Absorption included.
Sample focusing:
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.
Sample shape:
Sample shape may be a cylinder, a sphere, a box or any other shape
box/plate: xwidth x yheight x zdepth (thickness=0)
hollow box/plate:xwidth x yheight x zdepth and thickness>0
cylinder: radius x yheight (thickness=0)
hollow cylinder: radius x yheight and thickness>0
sphere: radius (yheight=0 thickness=0)
hollow sphere: radius and thickness>0 (yheight=0)
any shape: geometry=OFF file
The complex geometry option handles any closed non-convex polyhedra.
It computes the intersection points of the neutron ray with the object
transparently, so that it can be used like a regular sample object.
It supports the PLY, OFF and NOFF file format but not COFF (colored faces).
Such files may be generated from XYZ data using:
qhull < coordinates.xyz Qx Qv Tv o > geomview.off
or
powercrust coordinates.xyz
and viewed with geomview or java -jar jroff.jar (see below).
The default size of the object depends of the OFF file data, but its
bounding box may be resized using xwidth,yheight and zdepth.
Example: Incoherent(radius=0.05,focus_r=0.035, pack=1, target_index=1)
Incoherent(geometry="socket.off",focus_r=0.035, pack=1, target_index=1)
Input parameters
Parameters in boldface are required;
the others are optional.
Name
Unit
Description
Default
geometry
str
Name of an Object File Format (OFF) or PLY file for complex geometry. The OFF/PLY file may be generated from XYZ coordinates using qhull/powercrust
0
radius
m
Outer radius of sample in (x,z) plane
0
xwidth
m
Horiz. dimension of sample (bounding box if off file), as a width
0
yheight
m
Vert. dimension of sample (bounding box if off file), as a height. A sphere shape is used when 0 and radius is set
0
zdepth
bounding box if off file
[m] Depth of sample
0
thickness
m
Thickness of hollow sample
0
target_x
0
target_y
m
position of target to focus at
0
target_z
0
focus_r
m
Radius of disk containing target. Use 0 for full space
0
focus_xw
m
horiz. dimension of a rectangular area
0
focus_yh
m
vert. dimension of a rectangular area
0
focus_aw
deg
horiz. angular dimension of a rectangular area
0
focus_ah
deg
vert. angular dimension of a rectangular area
0
target_index
1
Relative index of component to focus at, e.g. next is +1
0
pack
1
Packing factor
1
p_interact
1
MC Probability for scattering the ray; otherwise transmit
1
f_QE
rest is elastic
[1] Fraction of quasielastic scattering
0
gamma
HWHM
[1] Lorentzian width of quasielastic broadening
0
sigma_abs
barns
Absorption cross section pr. unit cell at 2200 m/s
5.08
sigma_inc
barns
Incoherent scattering cross section pr. unit cell
5.08
Vc
AA^3
Unit cell volume
13.827
concentric
only for box, cylinder, sphere
[1] Indicate that this component has a hollow geometry and may contain other components. It should then be duplicated after the inside part
0
order
1
Limit multiple scattering up to given order 0:all (default), 1:single, 2:double, ...