Incoherent sample (such as Vanadium) sample, with quasielastic component.
Identification
Author: Kim Lefmann and Kristian Nielsen
Origin: Risoe
Date: 15.4.98
Version: $Revision$
Modification history:
Aziz Daoudaladine, ISIS, 2007: Added option to handle a spherical sample shape
Peter Christiansen, Risoe: Added outgoing polarization: P' = 1/3*P2/3P = 1/3P NB! As above multiple scattering is ignored .
Reynald Arnerin, ILL, 2008: Added option to handle a complex geometry (OFF files)
Description
A Doublecylinder 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 nonconvex 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
m
Depth of sample (bounding box if off file)
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
1
Fraction of quasielastic scattering (rest is elastic)
0
gamma
1
Lorentzian width of quasielastic broadening (HWHM)
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
1
Indicate that this component has a hollow geometry
and may contain other components. It should then be duplicated
after the inside part (only for box, cylinder, sphere)