[ Identification | Description | Input parameters | Links ]

# The `Source_div` Component

Neutron source with Gaussian or uniform divergence

## Identification

- Site:
- Author: KL
- Origin: Risoe
- Date: November 20, 1998

## Description

    The routine is a rectangular neutron source, which has a gaussian or uniform
    divergent output in the forward direction.
    The neutron energy is distributed between lambda0-dlambda and
    lambda0+dlambda or between E0-dE and E0+dE. The flux unit is specified
    in n/cm2/s/st/energy unit (meV or Angs).
    In the case of uniform distribution (gauss=0), angles are uniformly distributed
    between -focus_aw and +focus_aw as well as -focus_ah and +focus_ah.
    For Gaussian distribution (gauss=1), 'focus_aw' and 'focus_ah' define the
    FWHM of a Gaussian distribution. Energy/wavelength distribution is also
    Gaussian.

    Example: Source_div(xwidth=0.1, yheight=0.1, focus_aw=2, focus_ah=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 |
xwidth | m | Width of source |  |
yheight | m | Height of source |  |
focus_aw | deg | FWHM (Gaussian) or maximal (uniform) horz. width divergence |  |
focus_ah | deg | FWHM (Gaussian) or maximal (uniform) vert. height divergence |  |
E0 | meV | Mean energy of neutrons. | 0.0 |
dE | meV | Energy half spread of neutrons. | 0.0 |
lambda0 | Ang | Mean wavelength of neutrons (only relevant for E0=0) | 0.0 |
dlambda | Ang | Wavelength half spread of neutrons. | 0.0 |
gauss | 0|1 | Criterion: 0: uniform, 1: Gaussian distributions | 0 |
flux | 1/(s cm 2 st energy_unit) | flux per energy unit, Angs or meV | 1 |

AT ( | , | , |  | ) RELATIVE |  |
ROTATED ( | , | , |  | ) RELATIVE |

## Links

- Source code for `Source_div.comp`.

[ Identification | Description | Input parameters | Links ]