I am using the data of the output plots of the DepositionGeant4 module in modules.root to get acquainted with allpix squared and root.
Setup:
A timepix detector (mydetector) with a 256 x 256 pixel matrix with 55um x 55um pixels (active area about 14mm x 14mm) and the default sensor excess of 1mm on all sides, giving a total sensor area of about 16mm x 16mm. I set chip excess to 0um. A flat circular beam is used as the particle source, with a radius large enough the extend beyond the sensor edges but not the corners.
Expected behaviour:
The DepositionGeant4 output of the incident track positions should span the full sensor area. The beam centre, which is positioned at the centre of the sensor, should appear at the centre of the 2D histogram in my simulation setup: at (x, y) = (8mm, 8mm) if the axis runs from 0 to 16mm.
Observed behaviour:
-
Missing 1mm on all four edges. A 1mm wide band along each edge is cut off (lower x- and lower y-coordinate) or contains no hits (upper x- and upper y-coordinate). This corresponds to the sensor excess region of 1mm on each side. It appears the histogram dimensions are correct by extending to 16mm along the x- and y-axis.
From this, it appears that (0,0) coincides with the active pixel matrix (0,0) and not the sensor (0,0). This would not be a problem if the coordinates extend to (-1mm, -1mm) but now they cut off part of the incidences on the sensor.
Is this indeed an issue within allpix/geant4 or am I missing something/making a wrong assumption in my config?
As I cannot add files as a new user I have listed the file contents below
** simulation.conf **
[Allpix]
detectors_file = “detector.conf”
number_of_events = 20000
output_directory = “output”
random_seed = 5769309453296233042
[GeometryBuilderGeant4]
world_material = “vacuum”
#[VisualizationGeant4]
[ignore]
mode = “gui”
view_style = “wireframe”
trajectories_color_mode = “generic”
accumulate = 1
accumulate_time_step = 2s
[DepositionGeant4]
particle_type = “alpha”
source_energy = 5000keV
source_type = “beam”
source_position = 0mm 0mm -10mm
beam_direction = 0 0 1
beam_size = 10mm # change to 1mm or 0.1mm to see centre in plot
flat_beam = true
number_of_particles = 1
beam_divergence = 0mrad 0mrad
output_plots = true
output_plots_scale = 2750ke
log_level = WARNING
[DetectorHistogrammer]
name = “mydetector”
granularity = 256, 256
max_cluster_charge = 2750ke # approximately 10000 keV
** detector.conf **
[mydetector]
type = “timepix”
position = 0mm 0mm 0um
orientation_mode = “xyz”
orientation = 0deg 0deg 0deg
chip_excess_top = 0um
chip_excess_left = 0um
chip_excess_right = 0um
chip_excess_bottom = 0um
And an image of 2D histogram of track incidence positions highlighting the issue: https://image2url.com/r2/default/images/1773753933539-64f7c85d-4de7-4df0-9f23-a47f93e63fec.png
