Electromagnetic Calorimeter: This device measures the total energy of e⁺, e^- and photons. These particles produce showers of e⁺e^- pairs in the material. The strong electric field of the nucleus cause the electrons to radiate photons. The photons then make e⁺e^- pairs, which then radiate photons and so on. The process results in a shower of particles. The number of final e⁺e^- pairs is proportional to the energy of the initiating particle.