The `MCViNE_Phonon_IncoherentInelastic` Component

One-phonon incoherent inelastic scattering from a phonon DOS (incoherent approximation), optional Ef focusing.

Identification

Author: Fahima Islam (McStas port of the MCViNE phonon IncoherentInelastic / IncoherentInelastic_EnergyFocusing kernels; MCViNE by J. Y. Y. Lin et al.)
Origin: MCViNE, https://github.com/mcvine/mcvine (mccomponents/lib/kernels/sample/phonon/IncoherentInelastic.cc, IncoherentInelastic_EnergyFocusing.cc)
Date: 2026-09-29

Description

S_inc(Q,E) = exp(-2W) hbar^2Q^2/(2M) g(|E|)/|E| [n(E)+1 or n(E)] with the DOS
g(E) normalised to 1, Debye-Waller factor computed from the DOS (MCViNE
DWFromDOS), and the DOS preprocessed like MCViNE (resampled to >=500 points,
parabolic low-energy fit, normalised). The final direction is uniform over 4pi;
Ef is uniform in [Ei-Emax_dos, Ei+Emax_dos]. With dEf>0, Ef is restricted to
Ef +/- dEf/2 (MCViNE IncoherentInelastic_EnergyFocusing).
DOS file: 2 columns E [meV] g(E) (a '#...THz' comment switches the unit to THz)
or an MCViNE IDF binary 'DOS' file. Multiphonon terms are not included (see
Union IncoherentPhonon_process or NCrystal for those).

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_IncoherentInelastic(dos="MCViNE/Debye_dos.dat", T=300, average_mass=50.94, sigma_inc=10.1, sigma_abs=10.1, Vc=27.6, radius=0.01, yheight=0.05)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
dos	str	Phonon DOS file	0
T	K	Temperature	300
average_mass	amu	Average atomic mass	0
Ef	meV	Final energy for energy focusing (used when dEf>0)	0
dEf	meV	Full width of the final-energy window; 0 disables focusing	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_IncoherentInelastic Component

Identification

Description

Input parameters

Links

The `MCViNE_Phonon_IncoherentInelastic` Component