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McStas: Source_div Component

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

The Source_div Component

Neutron source with Gaussian or uniform divergence


  • Author: KL
  • Origin: Risoe
  • Date: November 20, 1998
  • Version:(Unknown)
  • Modification history:
    • KL, 8 October 2001


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

Example: Source_div(xwidth=0.1, yheight=0.1, focus_aw=2, focus_ah=2, E0=14, dE=2, gauss=0)

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

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 only relevant for E0=0 [Ang] Mean wavelength of neutrons 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

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 1 normalisation factor 1/'neutron_count'  


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

Generated automatically by McDoc, Peter Willendrup <> / Wed Jan 12 15:13:31 2022

Last Modified: Wednesday, 12-Jan-2022 16:13:31 CET
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