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

# The `Source_gen` Component

Circular/squared neutron source with flat or Maxwellian energy/wavelength spectrum (possibly spatially gaussian)

## Identification

- Author: Emmanuel Farhi, Kim Lefmann
- Origin: ILL/Risoe
- Date: Aug 27, 2001
- Version: 1.21
- 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).
    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 spatially uniform, but becomes gaussian if one of the source
    dimensions (radius, h or w) is negative, or you set the gaussian flag.
    Divergence profiles are triangular.
    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, T2=38, I1=1e13)
      Source_gen(h=0.1,w=0.1,Emin=1,Emax=3, I1=1e13, verbose=1, gaussian=1)
      EXTEND
      %{
         t = rand0max(1e-3); // set time from 0 to 1 ms for TOF instruments.
      %}

    Some sources parameters:
    PSI cold source T1=150.42,I1=3.67e11 T2=38.74,I2=3.64e11
                    T3=14.84,I3=0.95e11
    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

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
--- | --- | --- | ---
radius | m | Radius of circle in (x,y,0) plane where neutrons are generated. You may also use 'h' and 'w' for a square source | 0.0
dist | m | Distance to target along z axis. | 57.296
xw | m | Width(x) of target. If dist=0.0, xw = horz. div in deg | 0
yh | m | Height(y) of target. If dist=0.0, yh = vert. div in deg | 0
E0 | meV | Mean energy of neutrons. You may also use Lambda0. | 14.68
dE | meV | Energy spread of neutrons, half width. | 0
Lambda0 | AA | Mean wavelength of neutrons. | 2.36
dLambda | AA | Wavelength spread of neutrons,half width | 0.1627
I1 | 1/(cm**2*st*AA) | Source flux per solid angle, area and Angstrom | 0
h | m | Source y-height, then does not use radius parameter | 0
w | m | Source x-width, then does not use radius parameter | 0
gaussian | 0/1 | Use gaussian beam, normal distributions | 0
verbose | 0/1 | display info about the source. -1 unactivate source. | 0
T1 | K | Temperature of the Maxwellian source, 0=none | 0
Lmin | AA | Minimum wavelength of neutrons | 0
Lmax | AA | Maximum wavelength of neutrons | 0
Emin | meV | Minimum energy of neutrons | 0
Emax | meV | Maximum energy of neutrons | 0
T2 | K | Second Maxwellian source Temperature, 0=none | 0
I2 | 1/(cm**2*st*AA) | Second Maxwellian Source flux | 0
T3 | K | Third Maxwellian source Temperature, 0=none | 0
I3 | 1/(cm**2*st*AA) | Third Maxwellian Source flux | 0
length | m | Source z-length, not anymore flat | 0

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
p_in |  |  |
lambda0 |  |  |
lambda02 |  |  |
L2P |  |  |
lambda_0 |  |  |
d_lambda |  |  |
lambda0b |  |  |
lambda02b |  |  |
L2Pb |  |  |
lambda0c |  |  |
lambda02c |  |  |
L2Pc |  |  |

## 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 ]