Putting cosmic rays to work

These penetrating interstellar particles have applications from astronomy to archaeology

- Prof Lewis Dartnell

Cosmic rays are high-energy subatomic particles that zip around in outer space. They're accelerated to enormous speeds by astrophysical events like coronal mass ejections on the Sun or supernovae exploding across the Galaxy. When one encounters planet Earth, it soon hits a gas atom high in the atmosphere, creating a burst of other particles which themselves fly forwards to trigger further interactions, until a huge cone-shaped cascade of different particles develops.

This cosmic radiation is a hazard not just for astronauts, but also for passengers and aircrew flying high in the atmosphere - especially on routes over the poles, where the protection from the planet's magnetic field is weakest. Much of these 'secondary cascades' are absorbed by the atmosphere, but some of the more penetrating particles do reach Earth's surface, in particular muons, but also some neutrons, electrons and gamma rays.