The `MCViNE_Phonon_IncoherentElastic` Component

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.

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	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
sigma_abs	barn	Absorption cross section per unit cell at 2200 m/s	0
Vc	AA^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

AT (	,	,		) RELATIVE
ROTATED (	,	,		) RELATIVE

The MCViNE_Phonon_IncoherentElastic Component

Identification

Description

Input parameters

Links

The `MCViNE_Phonon_IncoherentElastic` Component