JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Dark matter detectors. Worker examining a row of dark matter scintillation detectors. Dark matter is the non-visible matter that is thought to make up most of the mass of the universe. Most candidates for dark matter are extremely difficult to detect, such as the exotic particles called weakly interacting massive particles (WIMPs). The signals from the rare detection of a WIMP need to be easily detected. This is done by scintillation, where a chemical (usually sodium iodide) reacts to such an event by emitting a flash of light. These detectors are being made for Boulby Underground Laboratory for Dark Matter Research, England. Photographed in 2003.
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