positrons and neutrons. This is very much like β + decay, where energy is used to convert a proton into a neutron, a positron ( e + ) and an electron neutrino ( ν e ) is emitted: From known β + decay: Energy + p → n + e + + ν e In the Cowan and Reines experiment, instead of an outgoing neutrino, you have an incoming antineutrino ( ν e ) from a nuclear reactor: Energy (&gt; 1.8 MeV ) + p + ν e → n + e + The resulting positron annihilation with electrons in the detector material created photons with an energy of about 0.5 MeV . Pairs of photons in coincidence could be detected by the two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei resulting in gamma rays of about 8 MeV that were detected a few microseconds after the photons from a positron annihilation event. Neutrinos' low mass and neutral charge mean they interact exceedingly weakly with other particles and fields. This feature of weak interaction interests scientists because it means neutrinos can be used to probe environments that other radiation (such as light or radio waves) cannot penetrate. Using neutrinos as a probe was first proposed in the mid 20th century as a way to detect conditions at the core of the Sun. The solar core cannot be imaged directly because electromagnetic radiation (such as light) is diffused by the great amount and density