About the adventures of a hadron in matter
Initially the hadron will fly in the substance without incident, just ripping electrons from orbits on its way if this is a charged hadron, such as a proton or pion. But when this left behind the path called the nuclear interaction length, it is likely to happen a strong interaction of the hadron with one of the substance’s nuclei, in which our hadron either disappears or loses a significant fraction of its energy. As a result, several newborn hadrons fly out of that nucleus and face the same fate. This is repeated several times, as long as after the next interaction hadrons emitted from a nucleus will be too slow to knock in turn new hadrons out of nuclei. That cascading process is called a hadron shower, and the trajectories of particles born in it form a sort of a tree spanning tens of centimeters. Should some of the newborn particles be neutral pions, these almost immediately decay into two photons, which give rise to an electromagnetic shower inside the hadron one.