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Awesome Detectors


The Ghost Particle homepage

Scientists estimate that many hundreds of billions of neutrinos will have harmlessly sped through your body by the time you finish reading this sentence. But despite their abundance, there's only a 10 percent chance over the course of your entire lifetime that even one of these invisible particles will ever (again, harmlessly) interact with any other particle in your body. Because of the rarity of collisions between neutrinos and matter—events that are necessary to perceive or study these spectral particles—neutrinos play an expert game of hard-to-get with physicists, who have designed giant, extremely sensitive detectors to seek them out. In this slide show, take a tour of some of the most intriguing neutrino experiments around the globe, and find out what tantalizing results keep the experts on the trail of the ghost particle.—Lexi Krock

Homestake
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Homestake
This experiment, now ended, was the first to detect neutrinos from the sun in the early 1970s. The Homestake detector, pioneered by Nobel laureate in physics Raymond Davis Jr., seen here, consisted of a tank of 615 tons of perchloroethylene, a dry-cleaning fluid. The tank was situated in the Homestake gold mine in South Dakota. On very rare occasions—about twice every three days—a neutrino would interact with a nucleus of chlorine in the liquid and produce a nucleus of radioactive argon. Davis developed techniques to extract the few atoms of argon created each month and count them by monitoring their radioactivity. He found fewer neutrinos than expected—the famous "solar neutrino problem," which was resolved conclusively in 2001-2002 by the Sudbury Neutrino Observatory.



KAMLAND
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KAMLAND
An international team of physicists completed construction on the KAMLAND detector—short for Kamioka Liquid-scintillator Anti-Neutrino Detector—in 1997 on the Japanese island of Honshu. KAMLAND detects antineutrinos, the antimatter opposites of neutrinos, which signal the latter's presence. The detector uses a telescope made of 1,000 tons of mineral oil and benzene in a stainless steel tank two thirds of a mile below the Earth's surface to measure antineutrinos issuing from nuclear power reactors and natural nuclear reactions. In July 2005, KAMLAND scientists measured the Earth's total radioactivity for the first time. Their findings will allow them to better understand what keeps the planet warm, the volcanoes active, the continents drifting, the magnetic field churning—all things that enable life. Until this discovery, geologists relied on the reverberations from earthquakes to estimate the planet's radioactivity.



ANTARES
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ANTARES
The aim of this experiment, whose acronym stands for the rather ungainly Astronomy with a Neutrino Telescope and Abyss environmental RESearch, is to answer questions about the composition of deep space by detecting neutrinos on the seafloor. ANTARES, scheduled for completion in 2006, will use water 8,200 feet below the surface of the Mediterranean off the south coast of France to detect the particles called muons, which are produced when neutrinos from space interact in Earth's core. Muons create radiation as they pass through water, and an array of approximately 1,000 photomultiplier tubes on 10 vertical strings spread over a mile and a half of seafloor sense and measure them. This image shows part of the ANTARES during installation in the Mediterranean.



ANITA
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ANITA
If it's successful, the ambitious and innovative ANITA neutrino detector will be the first device to identify so-called high-energy neutrinos created by collisions between cosmic rays and cosmic microwave photons in space. Studying neutrinos from these sources offers an unprecedented opportunity to learn about exotic objects at the edge of the universe, such as black holes. Beginning in 2006, ANITA will be a balloon-borne radio detector experiment circling the Antarctic continent at 115,000 feet during approximately 18-day missions. It will scan the vast expanses of ice for telltale pulses of radio emission generated by neutrino collisions.



MiniBoonE
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MiniBooNE
Like many detectors, this experiment at the Fermi National Accelerator in Batavia, Illinois investigates the oscillation of neutrinos from one type to another. Since 2003, it has observed neutrinos created from protons in Fermilab's particle booster, part of the system that the lab normally employs to accelerate protons to higher energies for other experiments. MiniBooNE is a 40-foot-in-diameter spherical steel tank filled with 800 tons of mineral oil and lined with 1,280 phototubes (some of which are being adjusted in this image) that produce a flash of light when charged particles travel through them. Analyses of these light flashes are already providing tantalizing information about the nonzero status of neutrino mass.



MINOS
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MINOS
MINOS, or Main Injector Neutrino Oscillation Search, is a two-detector experiment at Fermilab that began studying neutrino oscillations in 2003. It uses a beam of neutrinos that first pass through a detector at Fermilab, the inside of which is seen in this image, and then through one hundreds of miles away deep within the Soudan Iron Mine in northern Minnesota. The distance between the two detectors maximizes the probability that the neutrinos will have revealing interactions over the course of their journey. An international collaboration of particle physicists at Fermilab uses MINOS to investigate the puzzle of neutrino mass. The 98-foot-long detector consists of 486 massive octagonal planes, lined up like the slices of a loaf of bread. Each plane is made of a sheet of steel covered on one side with a layer of plastic that emits light when struck by a charged particle. MINOS will help researchers answer some of the fundamental questions of particle physics, especially how particles acquire mass.



Super-Kamiokande
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Super-Kamiokande
This detector began operating in 1996, more than half a mile underground in a zinc mine in Kamioka, Japan. Japanese and American scientists erected a huge tank of water 138 feet tall to hunt for neutrinos. The walls, ceiling, and floor of the 12.5-million-gallon tank are lined with 11,242 light-sensitive phototubes. These pick up and measure bluish streaks of light called Cherenkov radiation, which is left behind as neutrinos travel through the water. Super-Kamiokande detects neutrinos that nuclear interactions in the sun and atmosphere produce. In 2001, after several promising discoveries related to potential neutrino mass, the Super-Kamiokande was crippled when several thousand of its light detectors exploded. Repairs on the detector should be completed in 2007.



SNO
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SNO
The Sudbury Neutrino Observatory is a collaborative effort among physicists from Canada, the U.K., and the U.S. Using 1,000 tons of so-called heavy water and almost 10,000 photon detectors, they measure the flux, energy, and direction of solar neutrinos, which originate in the sun. SNO, located 6,800 feet underground in an active Ontario nickel mine, can also detect the other two types of neutrinos, muon neutrinos and tau neutrinos. In 2001, just two years after the observatory opened, physicists at SNO solved the 30-year-old mystery of the "missing solar neutrinos." They found that the answer lies not with the sun—where many physicists had suspected that solar neutrinos undergo changes—but with the journey they take from the core of the sun to the Earth.



AMANDA
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AMANDA
The South Pole is an inhospitable place to build and operate a telescope. But crystal-clear ice is an excellent medium for observing neutrinos as they pass through the Earth. Since 1999, AMANDA, the Antarctic Muon And Neutrino Detector Array (seen here during its assembly), has used the Antarctic ice to seek out neutrinos. When the particles interact in the ice they can produce muons, charged particles that are like electrons but heavier. The muons create faint flashes of light as they pass through the ice some 1.2 miles below the surface, where they are sensed by AMANDA's hundreds of light-sensitive phototubes supported on 19 tethers frozen in the ice. AMANDA's goal is to conduct neutrino astronomy, identifying and characterizing extra-solar sources of neutrinos, which could provide important clues in the search for dark matter.



IceCube
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IceCube
When it's completed in 2009, IceCube, an international neutrino experiment involving more than 20 research institutions, will become the largest particle detector ever built. Setting IceCube's 4,200 optical modules deep within the South Pole, where the detector joins its predecessor, AMANDA, will require drilling 70 holes a a mile and a half deep each using a novel hot-water drill, part of which is seen here. The detector's goal will be to investigate the still-mysterious sources of cosmic rays. IceCube's telescope will use the Antarctic ice to look for the signatures of cosmic neutrinos, elusive particles produced in violent cosmic events such as colliding galaxies, black holes, quasars, and other phenomena occurring at the margins of the universe.



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