We can’t see it or feel it but the surface of the Earth is constantly bombarded by a steady stream of subatomic particles from space called cosmic rays. These high energy particles originate in the powerful reactions in our Sun, from stars going supernova, and even as far back as the Big Bang. When subatomic particles like protons enter the Earth’s atmosphere, they create a secondary shower of particles, including muons that make up a large portion of the background radiation present on the Earth’s surface.
This invisible background radiation is the reason why sensitive astroparticle physics experiments probing the deepest mysteries of the universe have to be set up underground, shielded from muons and other particles. In fact, the two kilometres of rock overburden at SNOLAB reduces the muon flux by a factor of 50 million times, greater than any other lab on the planet.
In partnership with the Cosmic Rays Live outreach initiative at the Laboratori Nazionali del Gran Sasso (LNGS), a particle physics lab in Italy, SNOLAB is developing a new outreach program using a series of Cosmic Ray Cubes (CRC) that detect muons arriving on the Earth’s surface.
These CRCs function as muon telescopes. They are built using plastic scintillator, special wavelength shifting fibres, and silicon photomultipliers (SiPM). When muons (charged particles) pass through the detector, they trigger a reaction in the scintillating bars of the CRC, exciting electrons in the material. When this happens, photons of light are produced. These are shifted to a wavelength that the SiPMs are sensitive to.
The SiPMs transform the flash of light into an electrical signal, which contains information about the particle passing through the detector. The electrical signals are presented on the outside of the detector as a flash of light in a series of LEDs arranged in a grid in the x, y, and z planes of the detector. Recently, the CRC has been upgraded to include an auditory signal – for every muon that passes through the detector, a musical note is heard, creating a symphony of particles.
Anyone can view muon interactions in at participating labs around the world using their smartphone and the free Cosmic Rays Live mobile app, available on Google Play and the App Store. Live data can be viewed and downloaded from any of the telescopes, including one in the surface building at SNOLAB, one underground at Canfranc Underground Laboratory in Spain, or even one located in a subway station in Naples, Italy! This allows anyone to compare data from around the globe and investigate for themselves using live data and real science.