Operating nuclear reactors, through fission processes, produce large amounts of at low energy. Generally speaking, every 3 GW_th generates 6 x 10²⁰ per sec.

To detect produced by the nuclear reactor, a special kind of liquid called scintillator is used. When a passes through a volume of scintillator, a chain of reactions takes place and a shower of light is produced:

The first reaction above is the inverse β-decay reaction. This example is the chain of reactions that takes place in the Daya Bay detectors; the liquid scintillator used is a 0.1% Gd-doped liquid scintillator.

The shower of light is then collected by the photomultiplier tubes (PMTs) placed on the detector wall, producing signals that are sent to computers for analysis.