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

12.19  The Powder_process McStas Component

Port of the PowderN process to the Union components

Identification

Description

This Union_process is based on the PowderN.comp component originally written by P. Willendrup, L. Chapon, K. Lefmann, A.B.Abrahamsen, N.B.Christensen, E.M.Lauridsen.

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

Input file for reflections. No scattering if NULL or "" [string]

"NULL"

packing_factor

1

How dense is the material compared to optimal 0-1

1

Vc

Å\(^{3}\)

Volume of unit cell=nb atoms per cell/density of atoms.

0

delta_d_d

0/1

Global relative delta_d_d/d broadening when the ’w’ column is not available. Use 0 if ideal.

0

DW

1

Global Debye-Waller factor when the ’DW’ column is not available. Use 1 if included in F2

0

nb_atoms

1

Number of sub-unit per unit cell, that is ratio of sigma for chemical formula to sigma per unit cell

1

d_phi

deg

Angle corresponding to the vertical angular range to focus to, e.g. detector height. 0 for no focusing.

0

density

g/cm\(^{3}\)

Density of material. rho=density/weight/1e24*N_A.

0

weight

g/mol

Atomic/molecular weight of material.

0

barns

1

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

1

Strain

ppm

Global relative delta_d_d/d shift when the ’Strain’ column is not available. Use 0 if ideal.

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

format

no quotes

Name of the format, or list of column indexes (see Description).

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

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