Draft: DepositionGeant4: Allow for a beam of rectangular and elliptical shape.

The option of having a rectangle and ellipse beam in the DepositionGeant4 module was added. The histogram incident_track_position visualises the beam in 2D. Below, there are examples for the Rectangle and Ellipse beam.

The dimensions are specified with the beam_size parameter, by giving either one or two values. If only one value is specified the length in x and y are equal (the beam sigma in x and y for the ellipse). If two values are specified they should correspond to respective parameters in x and y.

As the beam_size key can take one or two parameters, backwards capability is ensured when going for the default circle beam with one beam_size value for the beam sigma in r.

One remaining issue is that for some reason the beam_size parameter when given two values, switches x and y. The configuration for the rectangle beam shown below was as follows:

[DepositionGeant4]
source_type = "beam"
flat_beam = true
particle_type = "e-"
source_energy = 5GeV
beam_size = 3mm 4mm
beam_shape = Rectangle
beam_direction = 0 0 1
model = "fixed"
source_position =  0 0 -10mm
output_plots = true

In the resulting plot, however, it is exactly the other way around with a length in x of 4mm and in y of 3mm.

incident_track_position_rectangle.pdfincident_track_position_ellipse.pdf