DAVID PARKER / SCIENCE PHOTO LIBRARY DAVID PARKER / SCIENCE PHOTO LIBRARY
WIMP detection. Technicians with shielding for a Weakly-Interacting Massive Particle (WIMP) detector at the UK Dark Matter Collaboration (UKDMC) project site at Boulby Mine, Britain. About 90% of the universe's mass may be invisible dark matter such as WIMPs. These "castles" surround each detector and are made of lead and copper blocks; each "castle" is then wrapped in wax of polythene. Together these shield the detector from natural radioactivity in the mine's walls. The detector measures the recoil energies of normal nuclei after they have been hit by a WIMP, a rare event due to the WIMP's weak interactions with other matter.
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