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14.6 The Source_gen4 McStas Component
Circular/squared neutron source with flat or Maxwellian energy/wavelength spectrum (possibly spatially gaussian)
Identification
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Author: Emmanuel Farhi, Kim Lefmann, modified to PSI use by Jonas Okkels Birk
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Origin: ILL/Risoe
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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 Å. 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(Å) flux(n/s/cm^2/st/Å)] 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/Å) 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 |
|
|
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|
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*Å)]. 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 |
Å |
Mean wavelength of neutrons. |
0 |
|
dLambda |
Å |
Wavelength spread of neutrons,half width |
0 |
|
I1 |
1/(cm**2*st) |
Source flux per solid angle, area and Å |
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 inactivate 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 |
Å |
Minimum wavelength of neutrons |
0 |
|
Lmax |
Å |
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*Å) |
Amplitude of heigh energy tail |
0 |
|
HEtailL0 |
Å |
Offset of heigh energy tail |
0 |
|
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Links
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Component source code found in file Source_gen4.comp.
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P. Ageron, Nucl. Inst. Meth. A 284 (1989) 197
