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The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond 1018 eV. In Earth's atmosphere such particles interact with air nuclei and produce various other particles. These effect particles (called an "air shower") can be detected and measured. But since these high energy particles have an estimated arrival rate of just 1 per km2 per century, the Auger Observatory has created a detection area of — the size of Rhode Island, or Luxembourg — in order to record a large number of these events. It is located in the western Mendoza Province, Argentina, near the Andes. Construction began in 2000,〔(News 20/12/13 )〕 the observatory has been taking production-grade data since 2005 and was officially completed in 2008. The observatory was named after the French physicist Pierre Victor Auger. The project was proposed by Jim Cronin and Alan Watson in 1992. Today, more than 500 physicists from nearly 100 institutions around the world〔(The Pierre Auger Collaboration: collaborators by institution )〕 are collaborating to maintain and upgrade the site in Argentina and collect and analyse the measured data. The 15 participating countries shared the $50 million construction budget, each providing a small portion of the total cost. == Physical background == From outer space, ultra-high-energy cosmic rays reach Earth. These consist of single sub-atomic particles (protons or atomic nuclei), each with energy levels beyond 1018 eV. When such a single particle reaches Earth atmosphere, it has its energy dissipated by creating billions of other particles: electrons, photons and muons, all near the speed of light. These particles spread longitudinal (perpendicular to the single particle incoming route), creating a forward moving plane of particles, with higher intensities near the axis. Such an incident is called an "air shower". Passing through the atmosphere, this plane of particles creates UV light, invisible to the human eye, called the fluorescing effect, more or less in the pattern of straight lightning traces. These traces can be photographed at high speed by specialised telescopes, called Fluorescence Detectors, overlooking an area with at a slight elevation. Then, when the particles reach the Earth surface, they can be detected when they arrive in a water tank, where they cause visible blue light due to the Cherenkov effect. A sensitive photoelectric tube can catch these impacts. Such a station is called a water Cherenkov Detector or 'tank'. The Auger Observatory has both types of detectors covering the same area, which allows for very precise measurements. When an air shower hits multiple Cherenkov Detectors on the ground, the direction of the ray can be calculated using basic geometrics. The longitudinal axis point can be determined from the ''densities'' in each affected ground station. Depending on the ''time difference'' of impact places, the angle of the axis can be determined. Only when the axis would be vertical, all ground detectors register at the very same moment in time, and any tilting of the axis will cause a time difference between earlierst and latest touchdown. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pierre Auger Observatory」の詳細全文を読む スポンサード リンク
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