When I was in high school I participated to the EEE project (Extreme Energy Events), which used various vapour chamber-like detectors scattered all around Italian schools to calculate the trajectories of muon showers produced by cosmic rays hitting the Earth's atmosphere. We used the trajectories to approximate where the cosmic ray hit the atmosphere. Turns out you have to take into account quite a lot of relativistic effects to get precise readings
Question: why muons? Why not electrons?
Or why not neutrons, which are not charged (hence should penetrate better, if I understand it correctly)?
Electrons can interact in additional ways, so they aren't as penetrating. Neutrons are rarer than muons in cosmic ray showers and are also much more difficult to detect.