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McStas: Phonon_simple Component

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

The Phonon_simple Component

A sample for phonon scattering based on cross section expressions from Squires, Ch.3.

Identification

  • Author: Kim Lefmann
  • Origin: Risoe
  • Date: 04.02.04
  • Version: $Revision$

Description

Single-cylinder shape.
Absorption included.
No multiple scattering.
No incoherent scattering emitted.
No attenuation from coherent scattering. No Bragg scattering.
fcc crystal n.n. interactions only
One phonon branch only -> phonon polarization not accounted for.
Bravais lattice only. (i.e. just one atom per unit cell)

Algorithm:
0. Always perform the scattering if possible (otherwise ABSORB)
1. Choose direction within a focusing solid angle
2. Calculate the zeros of (E_i-E_f-hbar omega(kappa)) as a function of k_f
3. Choose one value of k_f (always at least one is possible!)
4. Perform the correct weight transformation

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
radius m Outer radius of sample in (x,z) plane  
yheight m Height of sample in y direction  
sigma_abs barns Absorption cross section at 2200 m/s per atom  
sigma_inc barns Incoherent scattering cross section per atom  
a AA fcc Lattice constant  
b fm Scattering length  
M a.u. Atomic mass  
c meV/AA^(-1) Velocity of sound  
DW 1 Debye-Waller factor  
T K Temperature  
target_x m position of target to focus at . Transverse coordinate 0
target_y m position of target to focus at. Vertical coordinate 0
target_z m position of target to focus at. Straight ahead. 0
target_index 1 relative index of component to focus at, e.g. next is +1 0
focus_r m Radius of sphere containing target. 0
focus_xw m horiz. dimension of a rectangular area 0
focus_yh m vert. dimension of a rectangular area 0
focus_aw deg horiz. angular dimension of a rectangular area 0
focus_ah deg vert. angular dimension of a rectangular area 0

Output parameters

Name Unit Description Default
V_rho AA^-3 Atomic density  
V_my_s m^-1 Attenuation factor due to incoherent scattering  
V_my_a_v m^-1 Attenuation factor due to absorbtion  
DV  
parms  

Links


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

Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Wed Apr 19 10:57:33 2017


Last Modified: Wednesday, 19-Apr-2017 12:57:33 CEST
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