The geometry is a simple cylinder of homogeneous material.
The cylinder is replicated longitudinaly (slice) and radialy (ring),
in radiation length unit.
The pictures (G4) (G3)
show a cylinder of 20 slices of 1 radiation length, and
of 20 rings of 0.25 radiation length.
The incident particle is an electron of 5 GeV. Only the tracks of charged
particles are drawn.
The code of this example is in