Radioactive decay: the rarest event in the universe

A dark-matter detector picks up radioactive decay that takes place over trillions of years. Andrew Masterson reports.

radioactive decay
L' AQUILA, ITALY - MAY 23: View of the laboratory under Gran Sasso where experiments on the Germanium Detector Array (or GERDA), experiment is searching for neutrinoless double beta decay in Assergi (AQ) on May 23, 2018 Italy. Gran Sasso National Laboratory (LNGS) is the largest underground laboratory in the world devoted to neutrino and astroparticle physics, a worldwide research facility for scientists working in this field of research, where particle physics, cosmology and astrophysics meet. It is unequalled anywhere else, as it offers the most advanced underground infrastructures in terms of dimensions, complexity and completeness. (Photo by Stefano Montesi - Corbis/Corbis via Getty Images)