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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: $Revision$
  • 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 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

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'  


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

Generated automatically by McDoc, Peter Willendrup <> / Wed Apr 19 10:57:33 2017

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