Union process: Incoherent elastic scattering with Debye-Waller factor exp(-2W), 2W = dw_core*Q^2.
Author: Fahima Islam (McStas port of the MCViNE phonon IncoherentElastic kernel; MCViNE by J. Y. Y. Lin et al.)
Origin: MCViNE, https://github.com/mcvine/mcvine (mccomponents/lib/kernels/sample/phonon/IncoherentElastic.cc)
Date: 2026-09-29
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.
Union process. Part of the Union components: define this process, collect it into a material with Union_make_material (absorption is set there with my_absorption, the absorption inverse penetration depth at 2200 m/s), assign the material to Union_box/Union_cylinder/Union_sphere/Union_mesh geometries, and add a Union_master after them. Geometry, attenuation and multiple scattering are handled by Union_master; this component provides the MCViNE kernel: the scattering coefficient and the final-state sampling (weight). Isotropic process (powder/liquid-like); rotation is irrelevant. The kernel code is shared with the standalone component MCViNE_Phonon_IncoherentElastic (mcvine-lib.c). Uses share/mcvine-lib.h/.c and share/mcvine-union-lib.h/.c; the process type MCViNE is declared in share/union-lib.h and registered with Union_master in share/mcvine-union-lib.h.
Example: MCViNE_Phonon_IncoherentElastic_process(dw_core=0.0067, sigma_inc=10, Vc=27.6)
Parameters in boldface are required; the others are optional.
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Name |
Unit |
Description |
Default |
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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 |
|
Vc |
Å\(^{3}\) |
Unit cell volume |
0 |
|
packing_factor |
1 |
Packing factor (scales the scattering coefficient) |
1 |
|
interact_fraction |
1 |
Union: fraction of interactions forced to this process (-1: by cross section) |
-1 |
|
init |
string |
Deprecated and unused, accepted like on the other Union components (see Union_init). |
"" |
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Component source code found in file MCViNE_Phonon_IncoherentElastic_process.comp.
MCViNE documentation: https://mcvine.github.io