[ Identification | Description | Input parameters | Links ]

The MCViNE_DGSSXRes_process Component

Union process: Resolution kernel for direct-geometry single-crystal spectrometers (aims at a pixel and TOF window).

Identification

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

Description

Scatters towards a target disk (position target_x/y/z or target_index, radius
focus_r) and picks the arrival time at the target uniformly in
tof_at_target +/- dtof/2 (absolute neutron time, s). The final speed follows
from the flight distance. Weight: solid_angle/4pi * dtof * dE/dt * vf/vi, as in
MCViNE. Record ki/kf with monitors to build the resolution ellipsoid (similar
in purpose to McStas' TOFRes_sample, with MCViNE's weighting).

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 target is the Union focusing of the geometry (target_index / target_x.. and
focus_r / focus_xw,focus_xh / focus_aw,focus_ah on Union_box etc.).
The kernel code is shared with the standalone component MCViNE_DGSSXRes (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_DGSSXRes_process(focus_r=0.0125, tof_at_target=0.0052, dtof=1e-5, scattering_coefficient=10)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
tof_at_target	s	Desired absolute time of arrival at the target	0.001
dtof	s	Width of the time window	1e-5
scattering_coefficient	m^-1	Scattering coefficient (inverse penetration depth for scattering)	0
sigma_scat	barn	Alternative: scattering cross section per unit cell (used when Vc>0)	0
Vc	AA^3	Unit cell volume; when >0 the coefficient is sigma_scat/Vc	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).	""

AT (	,	,		) RELATIVE		Generate to clipboard
ROTATED (	,	,		) RELATIVE

Links

• Source code for MCViNE_DGSSXRes_process.comp.
• MCViNE documentation: https://mcvine.github.io

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[ Identification | Description | Examples | Input parameters | Links ]

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Last Modified: Tuesday, 06-Oct-2026 21:19:12 CEST