Neutron source with Gaussian or uniform divergence
Date: November 20, 1998
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
Parameters in boldface are required;
the others are optional.
Width of source
Height of source
FWHM (Gaussian) or maximal (uniform) horz. width divergence
FWHM (Gaussian) or maximal (uniform) vert. height divergence
Mean energy of neutrons.
Energy half spread of neutrons.
only relevant for E0=0
[Ang] Mean wavelength of neutrons
Wavelength half spread of neutrons.
Criterion: 0: uniform, 1: Gaussian distributions
1/(s cm 2 st energy_unit)
flux per energy unit, Angs or meV
parameter 'sigma' of the Gaussian distribution for horizontal divergence
parameter 'sigma' of the Gaussian distribution for vertical divergence