[ Identification | Description | Input parameters | Links ]

The `MCViNE_Phonon_IncoherentElastic_process` Component

Union process: Incoherent elastic scattering with Debye-Waller factor exp(-2W), 2W = dw_core*Q^2.

Identification

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

Description

Isotropic incoherent elastic scattering damped by the Debye-Waller factor.
dw_core [AA^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)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
dw_core	AA^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	AA^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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The MCViNE_Phonon_IncoherentElastic_process Component

Identification

Description

Input parameters

Links

The `MCViNE_Phonon_IncoherentElastic_process` Component