[ Identification | Description | Input parameters | Links ]

# The `Source_gen4` Component

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

## Identification

- Site:
- Author: Emmanuel Farhi, Kim Lefmann, modified to PSI use by Jonas Okkels Birk
- Origin: ILL/Risoe
- Date: Aug 27, 2001

## 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). And a high energytail of the shape A/(lambda0-lambda) can also be
    specified if you give an A. 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 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, 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= 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

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default |

flux_file

str

Name of a two columns [lambda flux] text file that contains the wavelength distribution of the flux in [1/(s*cm**2*st*AA)]. Comments (#) and further columns are ignored. Format is compatible with McStas/PGPLOT wavelength monitor files. When specified, temperature and intensity values are ignored. NO correction for solid-angle is applied, the intensity emitted into the chosen xw x yh rectangle at distance dist.

0

xdiv_file | str | Name of the x-horiz. divergence distribution file, given as a free format text matrix, preceeded with a line '# xylimits: xmin xmax xdiv_min xdiv_max' | 0 |
ydiv_file | str | Name of the y-vert. divergence distribution file, given as a free format text matrix, preceeded with a line '# xylimits: ymin ymax ydiv_min ydiv_max' | 0 |
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. | 0 |
xw | m | Width(x) of target. If dist=0.0, xw = full horz. div in deg | 0 |
yh | m | Height(y) of target. If dist=0.0, yh = full vert. div in deg | 0 |
E0 | meV | Mean energy of neutrons. | 0 |
dE | meV | Energy spread of neutrons, half width. | 0 |
Lambda0 | AA | Mean wavelength of neutrons. | 0 |
dLambda | AA | Wavelength spread of neutrons,half width | 0 |
I1 | 1/(cm**2*st) | 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 divergence 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 |
flux_file_perAA | 1 | When true (1), indicates that flux file data is already per Angstroem. If false, file data is per wavelength bin. | 0 |
flux_file_log | 1 | When true, will transform the flux table in log scale to improve the sampling. This may also cause | 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) | Second Maxwellian Source flux | 0 |
T3 | K | Third Maxwellian source Temperature, 0=none | 0 |
I3 | 1/(cm**2*st) | Third Maxwellian Source flux | 0 |
length | m | Source z-length, not anymore flat | 0 |
phi_init | degrees | Angle abowe the x-z-plan that the source is amied at | 0 |
theta_init | degrees | Angle from the z-axis in the x-z-plan that the source is amied at | 0 |
HEtailA | 1/(cm**2*st*AA) | Amplitude of heigh energy tail | 0 |
HEtailL0 | AA | Offset of heigh energy tail | 0 |

AT ( | , | , |  | ) RELATIVE |  |
ROTATED ( | , | , |  | ) RELATIVE |

## Links

- Source code for `Source_gen4.comp`.
- The ILL Yellow book
- P. Ageron, Nucl. Inst. Meth. A 284 (1989) 197

[ Identification | Description | Input parameters | Links ]