3.4  The Source_gen McStas Component

Circular/squared neutron source with flat or Maxwellian energy/wavelength spectrum

Identification

• Author: Emmanuel Farhi, Kim Lefmann

• 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. However, it may be directly set using the ’focus-aw’ and ’focus_ah’ parameters.

The neutron energy/wavelength is distributed uniformly in wavelength 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 per s. A Maxwellian spectra may be selected if you give the source temperatures (up to 3).

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.

Additional 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 yheight and xwidth parameters. The beam is divergence uniform,. The source may have a thickness, which will broaden the default zero time distribution.

Usage example: Source_gen(radius=0.1,lambda0=2.36,dlambda=0.16,T1=20,I1=1e13,focus_xw=0.01,focus_yh=0.01) Source_gen(yheight=0.1,xwidth=0.1,Emin=1,Emax=3,I1=1e13,verbose=1,focus_xw=0.01,focus_yh=0.01) EXTEND %{ t = rand0max(1e-3); // set time from 0 to 1 ms for TOF instruments. %}

Some neutron facility parameters:

PSI cold source     T1=296.2,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, 58 MW)  T3=16.7 ,I3=3.0423e+12
ILL HCS cold source T1=413.5,I1=10.22e12,T2=145.8,I2=3.44e13
(H5, 58 MW)  T3=40.1 ,I3=2.78e13
ILL Thermal tube    T1=683.7,I1=0.5874e+13,T2=257.7,I2=2.5099e+13
(H12, 58 MW) T3=16.7 ,I3=1.0343e+12
ILL Hot source      T1=1695, I1=1.74e13,T2=708,  I2=3.9e12 (58MW)
HZB cold source     T1=43.7 ,I1=1.4e12, T2=137.2,I2=2.08e12,radius=.155 (10MW)
HZB bi-spectral     T1=43.7, I1=1.4e12, T2=137.2,I2=2.08e12,T3=293.0,I3=1.77e12
HZB thermal tube    T1=293.0,I1=2.64e12 (10MW)
FRM2 cold,20MW      T1=35.0, I1=9.38e12,T2=547.5,I2=2.23e12,T3=195.4,I3=1.26e13
FRM2 thermal,20MW   T1=285.6,I1=3.06e13,T2=300.0,I2=1.68e12,T3=429.9,I3=6.77e12
LLB cold,14MW       T1=220,  I1=2.09e12,T2=60,   I2=3.83e12,T3=20,   I3=1.04e12
TRIGA thermal 1MW   T1=300,  I1=3.5e11 (scale by thermal power in MW)

%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.

Links

• Component source code found in file Source_gen.comp.

• P. Ageron, Nucl. Inst. Meth. A 284 (1989) 197

A general continuous source

This component is a continuous neutron source (rectangular or circular), which aims at a rectangular target centered at the beam. The angular divergence is given by the dimensions of the target. The shape may be rectangular (dimension \(h\) and \(w\)), or a disk of radius \(r\). The wavelength/energy range to emit is specified either using center and half width, or using minimum and maximum boundaries, alternatively for energy and wavelength. The flux spectrum is specified with the same Maxwellian parameters as in component Source_Maxwell_3 (refer to section 3.3).

Maxwellian parameters for some continuous sources are given in Table 3.5. As nobody knows exactly the characteristics of the sources (it is not easy to measure spectrum there), these figures should be used with caution.