Component Manual for the Neutron Ray-Tracing Package McStas, version 3.8.6

12.20  The Single_crystal_process McStas Component

Port of the Single_crystal component to the Union components

Identification

Description

This Union_process is based on the Single_crystal.comp component originally written by Kristian Nielsen

Part of the Union components, a set of components that work together and thus sperates geometry and physics within McStas. The use of this component requires other components to be used.

1) One specifies a number of processes using process components like this one 2) These are gathered into material definitions using Union_make_material 3) Geometries are placed using Union_box / Union_cylinder, assigned a material 4) A Union_master component placed after all of the above

Only in step 4 will any simulation happen, and per default all geometries defined before the master, but after the previous will be simulated here.

There is a dedicated manual available for the Union_components

Algorithm: Described elsewhere

Input parameters

Parameters in boldface are required; the others are optional.

Name

Unit

Description

Default

reflections

string

File name containing structure factors of reflections. Use empty ("") or NULL for incoherent scattering only

0

delta_d_d

1

Lattice spacing variance, gaussian RMS

1e-4

mosaic

arc minutes

Crystal mosaic (isotropic), gaussian RMS. Puts the crystal in the isotropic mosaic model state, thus disregarding other mosaicity parameters.

-1

mosaic_a

arc minutes

Horizontal (rotation around lattice vector a) mosaic (anisotropic), gaussian RMS. Put the crystal in the anisotropic crystal vector state. I.e. model mosaicity through rotation around the crystal lattice vectors. Has precedence over in-plane mosaic model.

-1

mosaic_b

arc minutes

Vertical (rotation around lattice vector b) mosaic (anisotropic), gaussian RMS.

-1

mosaic_c

arc minutes

Out-of-plane (Rotation around lattice vector c) mosaic (anisotropic), gaussian RMS

-1

mosaic_AB

arc_minutes, arc_minutes,1, 1, 1, 1, 1, 1

In Plane mosaic rotation and plane vectors (anisotropic), mosaic_A, mosaic_B, A_h,A_k,A_l, B_h,B_k,B_l. Puts the crystal in the in-plane mosaic state. Vectors A and B define plane in which the crystal roation is defined, and mosaic_A, mosaic_B, denotes the resp. mosaicities (gaussian RMS) with respect to the two reflections chosen by A and B (Miller indices).

{0,0, 0,0,0, 0,0,0}

recip_cell

1

Choice of direct/reciprocal (0/1) unit cell definition

0

barns

1

Flag to indicate if |F|^2 from ’reflections’ is in barns or fm^2. barns=1 for laz and isotropic constant elastic scattering (reflections=NULL), barns=0 for lau type files

0

ax

Å or Å\(^{-1}\)

Coordinates of first (direct/recip) unit cell vector

0

ay

Å or Å\(^{-1}\)

a on y axis

0

az

Å or Å\(^{-1}\)

a on z axis

0

bx

Å or Å\(^{-1}\)

Coordinates of second (direct/recip) unit cell vector

0

by

Å or Å\(^{-1}\)

b on y axis

0

bz

Å or Å\(^{-1}\)

b on z axis

0

cx

Å or Å\(^{-1}\)

Coordinates of third (direct/recip) unit cell vector

0

cy

Å or Å\(^{-1}\)

c on y axis

0

cz

Å or Å\(^{-1}\)

c on z axis

0

aa

deg

Unit cell angles alpha, beta and gamma. Then uses norms of vectors a,b and c as lattice parameters

0

bb

deg

Beta angle

0

cc

deg

Gamma angle

0

order

1

Limit multiple scattering up to given order (0: all, 1: first, 2: second, ...) (Not supported in Union)

0

RX

m

Radius of lattice curvature along X. flat when 0.

0

RY

m

Radius of lattice curvature along Y. flat when 0.

0

RZ

m

Radius of lattice curvature along Z. flat when 0.

0

powder

1

Flag to indicate powder mode, for simulation of Debye-Scherrer cones via random crystallite orientation. A powder texture can be approximated with 0

0

PG

1

Flag to indicate "Pyrolytic Graphite" mode, only meaningful with choice of Graphite.lau, models PG crystal. A powder texture can be approximated with 0

0

interact_fraction

1

How large a part of the scattering events should use this process 0-1 (sum of all processes in material = 1)

-1

packing_factor

1

How dense is the material compared to optimal 0-1

1

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