Catching Neutrinos

Neutrinos are the ghosts of the particle world. They almost never interact with other forms of matter, so they can pass through walls, planets, stars — and people: Trillions of them stream through your body every second.

Neutrinos are the most common particles in the universe other that particles of light. They have no electric charge, and almost no mass. They’re produced by the nuclear reactions in the cores of stars, as well as in giant stellar explosions. Since they zip through the outer layers of stars without stopping, they’re the only direct probes of what’s going on inside the stars. That makes them valuable for studying the stars.

But catching a ghost isn’t easy. Since neutrinos pass through normal matter without stopping, you can’t study them with normal detectors. Yet scientists have devised some clever ways to nab them.

Most of their detectors consist of giant tanks of liquid — from super-pure water to drycleaning fluid. The tanks are buried deep underground to screen out cosmic rays and other radiation. On the rare occasion that a neutrino does interact with an atom in the tank, it emits a flash of light. Instruments track where the flash came from.

Other detectors are buried in the ice at the south pole, or anchored to the bottom of the Mediterranean Sea. They look for a neutrino to zap atoms in the ice or seawater. And an even bigger one is being built in the Mediterranean — a new “trap” for catching ghosts.

Script by Damond Benningfield