Reflections around a dark matter detector
14 April 1999
Looking like part of some alien creature from science-fiction, multiple reflections appear in a vessel that will surround a detector to search for the mysterious "dark matter". This is matter that must exist to explain the motions of stars and galaxies, but which we cannot see through its radiations. It may consist of weakly interacting massive particles (WIMPS), and these could be detected when a WIMP collides with an atom in a detector and the atom recoils. Physicists at the Rutherford Appleton Laboratory (RAL) and Imperial College, London, are building a detector containing liquid xenon, which will scintillate (flash light) each time a WIMP hits an atom.
This image shows the inside of the vessel that will surround the liquid xenon detector. It will contain 1000 litres of a paraffin-oil-based liquid that will also scintillate - but in this case the scintillations will indicate unwanted interactions in order to eliminate them. Reflected in the walls of the vessel are the gold-brown ends of photomultiplier tubes that will detect the scintillation light. Also multiply-reflected, so that they look almost organic, are pipes that will bubble nitrogen through the liquid scintillator once the vessel has been filled. (The nitrogen replaces oxygen in the scintillator, and so increases the amount of light of emitted.) One of these tubes, with several holes, is directly visible near the top centre of the image. When complete, the detector will be installed in the UK Dark Matter Collaboration's underground laboratory in the Boulby Mine in North Yorkshire.
Credit: Email Igor Liubarsky, RAL
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