Angle calculation

Dear colleagues,

I have a simple setup: a single Timepix detector is tilted by some angle and there is a particle source. For charge particles, I calculate the theta angle using the start and the end coordinates of the MCParticle object (I select only primaries). It works well, but for neutral, e.g. gammas it does not work for obvious reasons. So, I tried to calculate the angle by using the start point of MCTrack as the first point (the point where the particle was created) and the start point of MCParticle as the second point (the point where the first interaction has happened), both in global coordinates. But, it does not work as expected.

Please, guide me in the right direction. Thank you in advance!

Here are some important parameters:

physics_list = FTFP_BERT_EMZ
#physics_list = FTFP_BERT_LIV
particle_type = “gamma”
#particle_type = “mu-”
source_energy = 316keV
#source_energy = 4GeV
source_position = 550um 1100um -15cm
source_type = “beam”
beam_size = 100um
beam_direction = 0 0 1
beam_divergence = 50mrad 50mrad
number_of_particles = 1
max_step_length = 5um
fano_factor = 0.15
charge_creation_energy = 4.43eV
range_cut = 200um

type = “timepix_CdTe”
position = 0 0 0
#orientation = 0 0 0
orientation = 0 60deg 0

Dear @psmolyan

I fear I need some more information to help you here. Could you describe a bit more in detail what doesn’t work? What do you get out when you check the MCTrack::getStartPoint() and MCTrack::getEndPoint() (or MCParticle::getGlobalStartPoint()) and compare them?

Do you maybe have a plot illustrating the issue?

Best regards,

Dear Simon,

thank you for your suggestions, thanks to which I found the problem.

I have two simulated datasets for detector tilted at 60 degrees, for the first set – photon beam divergence is 1 mrad, for the second – 50 mrad. I was expecting that the difference in theta angle of photons for these two case should be greater, but … it is not. Finally, I calculated the angle by using the start point of MCTrack and the start point of MCParticle.

Best regards,

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