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

The Source_gen Component

Identification

• Author: Emmanuel Farhi, Kim Lefmann, edits Jonas O Birk
• Origin: ILL/Risoe
• Date: Aug 27, 2001
• Version: 1.41
• Modification history:
  • EF, Aug 27, 2001 ; can use Energy/wavelength and I1
  • EF, Sep 18, 2001 ; corrected illumination bug. Add options
  • EF, Oct 30, 2001 ; minor changes. mccompcurname replaced

Description

This routine is a neutron source (rectangular or circular), which aims at
a square target centered at the beam (in order to improve MC-acceptance
rate). The angular divergence is then given by the dimensions of the
target.
The neutron energy/wavelength is distributed between Emin=E0-dE and
Emax=E0+dE or Lmin=Lambda0-dLambda and Lmax=Lambda0+dLambda. The I1 may
be either arbitrary (I1=0), or specified in neutrons per steradian per
square cm per Angstrom. A Maxwellian spectra may be selected if you give
the source temperatures (up to 3). A high-energy tail of shape 
A/(lambda0-lambda) is added by setting the HEtailA and HEtailL0 parameters.
Finally, a file with the flux as a
function of the wavelength [lambda(AA) flux(n/s/cm^2/st/AA)] may be used
with the 'flux_file' parameter. Format is 2 columns free text.
Additionl distributions for the horizontal and vertical phase spaces
distributions (position-divergence) may be specified with the
'xdiv_file' and 'ydiv_file' parameters. Format is free text, requiring
a comment line '# xylimits: pos_min pos_max div_min div_max' to set
the axis of the distribution matrix. All these files may be generated using
standard monitors (better in McStas/PGPLOT format), e.g.:
  Monitor_nD(options="auto lambda per cm2")
  Monitor_nD(options="x hdiv, all auto")
  Monitor_nD(options="y vdiv, all auto")
The source shape is defined by its radius, or can alternatively be squared
if you specify non-zero h and w parameters.
The beam is divergence uniform,.
The source may have a thickness, which will broaden the default zero time
distribution.
For the Maxwellian spectra, the generated intensity is dPhi/dLambda (n/s/AA)
For flat spectra, the generated intensity is Phi (n/s).

Usage example:
  Source_gen(radius=0.1,Lambda0=2.36,dLambda=0.16,T1=20,I1=1e13,xw=0.01,yh=0.01)
  Source_gen(h=0.1,w=0.1,Emin=1,Emax=3,I1=1e13,verbose=1,xw=0.01,yh=0.01)
  EXTEND
  %{
     t = rand0max(1e-3); // set time from 0 to 1 ms for TOF instruments.
  %}

Some sources parameters:
PSI cold source T1= 296.16, I1=8.5E11, T2=40.68, I2=5.2E11
ILL VCS cold source T1=216.8,I1=1.24e+13,T2=33.9,I2=1.02e+13
       (H1)         T3=16.7 ,I3=3.0423e+12
ILL HCS cold source T1=413.5,I1=10.22e12,T2=145.8,I2=3.44e13
       (H5)         T3=40.1 ,I3=2.78e13
ILL Thermal tube    T1=683.7,I1=0.5874e+13,T2=257.7,I2=2.5099e+13
       (H12)        T3=16.7 ,I3=1.0343e+12
ILL Hot source      T1=1695,I1=1.74e13,T2=708,I2=3.9e12

%VALIDATION
Feb 2005: output cross-checked for 3 Maxwellians against VITESS source
          I(lambda), I(hor_div), I(vert_div) identical in shape and absolute values
Validated by: K. Lieutenant

Input parameters

Output parameters

Links

• Source code for Source_gen.comp.
• The ILL Yellow book
• P. Ageron, Nucl. Inst. Meth. A 284 (1989) 197

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