[ Identification | Description | Examples | 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

Examples

(Test cases in bold)

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	AA	Mean wavelength of neutrons (only relevant for E0=0)	0.0
dlambda	AA	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		Generate to clipboard
ROTATED (	,	,		) RELATIVE

Links

• Source code for Source_div.comp.

---

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

Generated on mcstas 3.8.4

---

Last Modified: Friday, 11-Sep-2026 15:00:08 CEST