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

# The `Source_div` Component

Neutron source with Gaussian or uniform divergence

## Identification

- Author: KL
- Origin: Risoe
- Date: November 20, 1998
- Version: 1.22
- Modification history:
  - KL, 8 October 2001

## Description

    The routine is a rectangular neutron source, which has a gaussian or uniform
    divergent output in the forward direction.
    The neutron energy is uniformly distributed between E0-dE and E0+dE or
    a wavelength is uniformly distributed between Lambda0-dLambda and Lambda0+dLambda.
    If energy and wavelength are given, energy is used.
    In the case of uniform distribution (gauss=0), angles are uniformly distributed
    between -hdiv and +hdiv as well as -vdiv and +vdiv. For Gaussian distribution
    (gauss=1), 'hdiv' and 'vdiv' define the FWHM of a Gauss'schen distribution,

    Example: Source_div(width=0.1, height=0.1, hdiv=2, vdiv=2, E0=14, dE=2, gauss=0)

    %VALIDATION
    Feb 2005: tested by Kim Lefmann    (o.k.)
    Apr 2005: energy distribution used in external tests of Fermi choppers (o.k.)
    Jun 2005: wavelength distribution used in external tests of velocity selectors (o.k.)
    Validated by: K. Lieutenant

    %BUGS
    distribution is uniform in (hor. and vert.) angle (relative to moderator normal),
    therefore not suited for large angles

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
--- | --- | --- | ---
width | m | Width of source |
height | m | Height of source |
hdiv | deg | FWHM (Gaussian) or maximal (uniform) horizontal divergence |
vdiv | deg | FWHM (Gaussian) or maximal (uniform) vertical divergence |
E0 | meV | Mean energy of neutrons. | 0.0
dE | meV | Energy spread of neutrons. | 0.0
Lambda0 | Ang | Mean wavelength of neutrons (only relevant for E0=0) | 0.0
dLambda | Ang | Wavelength spread of neutrons. | 0.0
gauss | - | Criterion: 0: uniform, 1: Gaussian distribution (default) | 1

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
sigmah | rad | parameter 'sigma' of the Gaussian distribution for horizontal divergence |
sigmav | rad | parameter 'sigma' of the Gaussian distribution for vertical divergence |
p_init | - | normalisation factor 1/'neutron_count' |

## Links

- Source code for `Source_div.comp`.

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