Rattling WIMPs.Rattling WIMPs Astronomers and physicists now have a number of interlockingreasons for believing that most of the universe--up to 90 percent--is made of matter that we can't see and that most likely is much more exotic than the stuff ordinary atoms are made of. A candidate for the dark matter that is receiving a good dealof attention now among physicists is the class of hypotehtical subatomic particles called WIMPs, or weakly interacting massive particles. Blas Cabrera Blas Cabrera is a physicist at Stanford University best known for his experiment in search of magnetic monopoles. He is the son of Spanish physicist Nicolás Cabrera. of Stanford University Stanford University, at Stanford, Calif.; coeducational; chartered 1885, opened 1891 as Leland Stanford Junior Univ. (still the legal name). The original campus was designed by Frederick Law Olmsted. David Starr Jordan was its first president. has developed a new class of particle detector particle detector, in physics, device for detecting, measuring, and analyzing particles and other forms of radiation entering it. Such devices play an important role not only in basic research, as in the study of elementary particles, but also in numerous that uses the acoustical effects of passing WIMPs on solid crystals to determine their presence. The existence of WIMPs has not yet been directly demonstrated. Cabrera's experiment is intended both to demonstrate their existence and to show that they inhabit the universe in sufficient numbers to do what cosmologists want them to do: namely, make the universe close on itself. Up to now, detectors for subatomic particles have generallyused either the particles' optical effects or electrical effects to determine their presence. WIMPs, being weakly interacting, almost never have these effects. However, WIMPs are massive--10 or more times as heavy as a proton--so, as they pass through a crystal of silicon, they can give an electron or an atomic nucleus Atomic nucleus The central region of an atom. Atoms are composed of negatively charged electrons, positively charged protons, and electrically neutral neutrons. a bump from which it will recoil recoil /re·coil/ (re´koil) a quick pulling back. elastic recoil the ability of a stretched object or organ, such as the bladder, to return to its resting position. . The bump becomes a vibration, called a phonon phonon (fō`nŏn), quantum of vibrational energy. The atoms of any crystal are in a state of vibration, their average kinetic energy being measured by the absolute temperature of the crystal. , that rattles along the lattice of the crystal. At the face of the crystal, the phonon will strike a superconducting aluminum tunnel junction, which will record its presence. |
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