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14.123 The MCViNE_Phonon_IncoherentElastic McStas Component
Incoherent elastic scattering with Debye-Waller factor exp(-2W), 2W = dw_core*Q^2.
Identification
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Author: Fahima Islam (McStas port of the MCViNE phonon IncoherentElastic kernel; MCViNE by J. Y. Y. Lin et al.)
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Origin: MCViNE, https://github.com/mcvine/mcvine (mccomponents/lib/kernels/sample/phonon/IncoherentElastic.cc)
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Date: 2026-09-29
Description
Isotropic incoherent elastic scattering damped by the Debye-Waller factor. dw_core [Å^2] is given directly, or (dw_core<0) computed from a phonon DOS, temperature and average atomic mass exactly as MCViNE’s DWFromDOS. McStas’ Incoherent has no Debye-Waller factor.
Transport (same as MCViNE HomogeneousNeutronScatterer): on the first passage the neutron is forced to scatter at a uniformly chosen depth, weighted by path length, attenuation exp(-(mu+sigma)x) and the scattering coefficient; on exit it is attenuated by exp(-(mu+sigma)L_out). With order>1 further scatterings are sampled analogically (truncated exponential). With p_transmit>0 that fraction of events is kept as the attenuated direct beam. mu(v) = absorption_coefficient*2200/v. Events for which the kernel cannot scatter (kinematically forbidden) are absorbed.
Geometry: box (xwidth,yheight,zdepth), cylinder (radius,yheight), hollow cylinder (+thickness) or sphere (radius only). All vectors (Q, targets, reciprocal vectors, atom positions) are in the component’s local frame.
Uses the shared runtime share/mcvine-lib.h/.c.
Example: MCViNE_Phonon_IncoherentElastic(dw_core=0.0067, sigma_inc=10, sigma_abs=10, Vc=27.6, radius=0.01, yheight=0.05)
Input parameters
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
|
|
|||
|
dw_core |
Å\(^{2}\) |
Debye-Waller core u^2 (2W = dw_core*Q^2); <0: compute from dos |
-1 |
|
dos |
str |
Phonon DOS file (2-column E[meV] g, or MCViNE IDF DOS) for dw_core<0 |
0 |
|
T |
K |
Temperature (for dw_core from DOS) |
300 |
|
average_mass |
amu |
Average atomic mass (for dw_core from DOS) |
0 |
|
sigma_inc |
barn |
Incoherent scattering cross section per unit cell |
0 |
|
sigma_abs |
barn |
Absorption cross section per unit cell at 2200 m/s |
0 |
|
Vc |
Å\(^{3}\) |
Unit cell volume |
0 |
|
radius |
m |
Outer radius of a cylinder (with yheight) or of a sphere (yheight=0) |
0 |
|
xwidth |
m |
Width of a box sample |
0 |
|
yheight |
m |
Height of a box or cylinder sample |
0 |
|
zdepth |
m |
Depth of a box sample |
0 |
|
thickness |
m |
Wall thickness of a hollow cylinder (0: filled) |
0 |
|
pack |
1 |
Packing factor (scales absorption and scattering coefficients) |
1 |
|
p_transmit |
1 |
Monte Carlo fraction of events kept as unscattered transmitted beam (0: always scatter) |
0 |
|
order |
1 |
Maximum number of scattering events per neutron (1: single scattering) |
1 |
|
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Links
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Component source code found in file MCViNE_Phonon_IncoherentElastic.comp.
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MCViNE documentation: https://mcvine.github.io
