Question

How to produce gamma rays

Answer 1

In gamma-ray astronomy, "particle-particle collision" usually means a high-energy proton, or cosmic ray, strikes another proton or atomic nucleus. This collision produces, among other things, one or more neutral pi mesons (or pions). These are unstable particles that decay into a pair of gamma rays. Since the pion is usually moving at a high velocity as a result of its violent birth, the gamma rays are projected forward in a slight "V" formation. This process gives rise to gamma rays with a broad spectrum of energies (all greater than 72 mega-electron-volts, which is a measurement of the kinetic energy in the incident particles).