Neutrino telescope

Neutrino telescope

In astronomy, a neutrino telescope is usually a detector consisting of a large mass of water or ice, surrounded by an array of sensitive light detectors known as photomultiplier tubes. This allows the observation of astronomical objects by detecting the neutrinos they emit, rather than their light (or photons) as in an ordinary telescope. The field of neutrino astronomy is still very much in its infancy: the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A.

Detector design

The GALLEX experiment used about 30 tons of gallium as reaction mass. A neutrino is able to react with an atom of gallium-71, converting it into an atom of the unstable isotope germanium-71. The germanium was then chemically extracted and concentrated. Neutrinos were thus detected by measuring the radioactive decay of germanium. This experiment is difficult to scale up due to the prohibitive cost of gallium. Larger experiments have therefore turned to a cheaper reaction mass.

The currently most common detector design consists of a large mass of water or ice, surrounded by an array of sensitive light detectors known as photomultiplier tubes. This design takes advantage of the fact that particles produced in the interaction of the incoming neutrino with an atomic nucleus typically travel faster than the speed of light in the detector medium (though of course slower than the speed of light in a vacuum). This generates an "optical shockwave" known as Čerenkov radiation which can be detected by the photomultiplier tubes.

The Super-Kamiokande neutrino detector uses 50,000 tons of pure water surrounded by 11,000 photomultiplier tubes buried 1 km underground. It is able to detect the incident direction of incoming neutrinos by detecting which photomultipliers fire. Kamiokande, the predecessor of Super-Kamiokande, was able to detect the burst of neutrinos associated with supernova 1987A, and in 1988 it was used to directly confirm the production of solar neutrinos.

The Antarctic Muon And Neutrino Detector Array (AMANDA) operated from 1996 to 2004. This detector used photomultiplier tubes mounted on strings, buried deep (1.5-2km) inside the glacial ice at the South Pole in Antarctica. The ice itself is used as the detector mass. The direction of incident neutrinos is determined by recording the arrival time of individual photons using a three-dimensional array of detector modules containing one photomultiplier tube each. This method allows detection of neutrinos above 50 GeV with a spatial resolution of approximately 2 degrees. AMANDA has been used to generate neutrino maps of the northern sky in order to search for extraterrestrial neutrino sources and in searches for dark matter. AMANDA is currently in the process of being upgraded to the IceCube observatory, eventually increasing the volume of the detector array to one cubic kilometer.

In the Mediterranean Sea, the ANTARES telescope is fully operational since May 30th, 2008. This telescope uses the sea water as the detector mass.

Neutrino telescopes

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