> The amount of photons in the scintillator is proportional to the energy deposited. Exactly: it is proportional to the energy deposited in the scintillator! W

> The amount of photons in the scintillator is proportional to the energy deposited. Exactly: it is proportional to the energy deposited in the scintillator! Which, for a cosmic ray, can be a tiny fraction of the total energy. In order to measure the kinetic energy of a particle, you need to stop it. In that case, your detector is called a calorimeter.