[ 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: 1.4

## 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_o | m | Outer radius of sample in (x,z) plane |
h | m | Height of sample in y direction |
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 [m] | 0
focus_aw | m | horiz. angular dimension of a rectangular area [deg] | 0
focus_ah | m | vert. angular dimension of a rectangular area [deg] | 0
sigma_a | barns | Absorption cross section at 2200 m/s per atom |
sigma_i | barns | Incoherent scattering cross section per atom |
a | fcc | [AA] 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 [m]. Vertical coordinate | 0
target_z | m | position of target to focus at [m]. Straight ahead. | 0
target_index |  |  | 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 | m^-1 | Attenuation factor due to absorbtion |

## Links

- Source code for `Phonon_simple.comp`.

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