Nuclear reactors, through fission processes, produce large amounts of at low energy. Generally speaking, every 3GW_th generates 6x10²⁰ 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 reaction 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 the 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 sent to computers for analysis.