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A neutrino observatory is a device to detect neutrinos from the Sun and other distant sources. They generally consist of a substantial body (tons) of some dense, transparent substance surrounded by sensitive instruments to detect electromagnetic radiation, such as photomultiplier tubes, the amount and type of substance chosen to result in occasional observable reactions to passing neutrinos. Some particular chemicals react more easily to neutrinos, but lake and sea water and ice have been used merely because large amounts are available naturally. The detectors also sense cosmic rays so detections must be analyzed regarding which type of particle was detected and/or the detector must be arranged so as to minimize the cosmic rays reaching it. Neutrinos can pass through substantially more material untouched than do cosmic rays, so the latter are vastly reduced by burying the detector underground or placing it at the bottom of substantial water. Neutrino observatories are also often designed so they easily detect particles from below, using the entire Earth to filter out other particles. Some example past, existing and proposed neutrino observatories:
The term neutrino experiment can refer to such an observatory but also applies to somewhat similar detectors that are in the trajectory of a source of neutrinos on Earth, such as an atomic reactor, or a sample of radioactive substance that emits neutrinos during beta decay. Such experiments are to determine characteristics of neutrinos such as their mass ranges and whether they are Majorana particles. Some existing and proposed such neutrino experiments:
The first attempts to detect neutrinos from off Earth (and the first such neutrinos detected) are those emitted by the Sun. Neutrinos from SN 1987A were detected by happenstance, and current efforts such as Ice Cube are intended to detect more such supernova neutrinos as well as those from any other distant astronomical neutrino sources, which are referred to as astrophysical neutrinos.