[Above] SNO: nearly 10,000 photomultipliers peer into an acrylic sphere 12 meters in diameter, filled with heavy water.
Rock & Ice

by Paul Preuss

What kind of science is easiest to do under a couple of kilometers of solid Canadian granite or Antarctic ice? The kind of particle physics that needs a really good filter, for one.

Neutrinos (and antineutrinos) are produced in many natural processes at many different energies-by radioactive decay, by the impact of cosmic rays in the atmosphere, in the heart of the sun, in cataclysmic events in the far reaches of space. but wherever they start, neutrinos are hard to stop. Virtually massless, feeling neither the electromagnetic force nor the strong nuclear force, neutrinos-at least the low-energy ones-could easily pass through a light-year of lead. Only their teeming ubiquity ensures that occasionally one is snagged in a weak interaction.