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I have a question about : gps/pos/ I would like to model a monochromatic beam with a Gaussian geometry (Gaussian symmetric shape in a XY plane perpendicular to the direction of propagation Z). The FWHM is the same in both directions X and Y, of 1 micrometer. So sigma = 1/2.355 =0.4246 micrometers. The beam is purely Gaussian, there is no central circular plateau.
Example 31 of the Gant4 toolkit is very close to what I would like to do:
# the beam spot is centered at the origin and is
# of 1d gaussian shape with a 1 mm central plateau
/gps/pos/centre 0. 0. 0. mm
# Should I comment this line? /gps/pos/radius 1. mm
/gps/pos/sigma_r .4246 um
So my question is: Should I comment the line with radius, since our beam does not have a central plateau? Or should I take a radius with a very small value compared to sigma_r ? (otherwise we would define a circle shape without radius, which would maybe be not possible ?)Or is there another shape than "circle" for a pure Gaussian shape ? Thank you