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McStas: Incoherent Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The Incoherent Component

Incoherent sample (such as Vanadium) sample, with quasielastic component OR or global energy transfer.


  • 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)


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 < Qx Qv Tv o >
  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="",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
Etrans meV Global energy-transfer, for use in inelastic settings 0
deltaE meV Width in energy around Etrans, for use in inelastic settings 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, ... 0


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <> / Wed Jan 12 15:13:20 2022

Last Modified: Wednesday, 12-Jan-2022 16:13:20 CET
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