Seven questions about the technologies and experiments that have detected neutrinos over seven decades — Cowan-Reines, water Cherenkov, ice Cherenkov, heavy water, liquid scintillator, and the underground labs that host them all.
No tricks — just check your knowledge of how each major detector works.
They used liquid scintillator with dissolved cadmium chloride. The signature: a prompt positron annihilation flash, then a delayed neutron-capture flash on cadmium ~microseconds later. The coincidence is unique to antineutrino events.
Super-K is a water Cherenkov detector. When a neutrino interaction produces a fast charged particle, the particle emits a cone of Cherenkov radiation (blue light), which the surrounding photomultiplier tubes detect.
IceCube uses Antarctic glacial ice as its Cherenkov medium — a cubic kilometer of it. Photomultiplier tubes are frozen into vertical strings of borehole holes, creating a 3D grid.
SNO's 1000 tonnes of heavy water (D₂O) borrowed from the Canadian reactor program. Neutrons in deuterium nuclei undergo neutral-current scattering, ν_x + d → p + n + ν_x, which is flavor-blind. This is what allowed Arthur McDonald's group to prove oscillation in 2001.
JUNO is 20,000 tonnes of ultrapure liquid scintillator in a 35-m-diameter acrylic sphere, 53 km from two reactor complexes in Jiangmen, China. Its primary goal: mass-ordering determination from precision reactor antineutrino spectroscopy.
Cosmic-ray muons at the surface arrive at ~1 per cm² per second — much faster than the neutrino event rate. The kilometer-scale rock overburden of an underground lab reduces the muon flux by a factor of ~10⁶, making neutrino events detectable above background.
A track event is a long, bright, straight-line trail of Cherenkov light along a muon's path through the ice. Produced by ν_μ charged-current interactions. Other types (electron, tau at lower energy) make roughly spherical "cascade" events instead.