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A neutrino is a neutral particle with very low mass, possibly zero. It has spin 1/2 and so is a fermion. It does not interact with the strong force or the electromagnetic force, but does interact with the weak force (and with gravity if it turns out to have mass).

Because the neutrino only interacts with the weak nuclear force, when moving through matter its chance of actually reacting with it are very low; the great of majority flies through anything without effect. It would take a light year of lead to block half the neutrinos flowing through it. Neutrino detectors therefore typically contain hundreds of tons of a material constructed so that a few atoms per day would interact with the incoming neutrinos.

It comes in three varieties, the electron neutrino νe, the muon neutrino νμ, and the tau neutrino ντ. Theoretical physicists believe that there is a possibility that neutrinos can 'oscillate' between the three types; however, this is only possible if neutrinos have non-zero mass, which is not yet known. The question of neutrino mass also has cosmological significance. If the neutrino does have mass, then it could make up a signficant fraction of the mass of the universe and help resolve the dark matter problem.

Neutrino detectors

There are several types of neutrino detectors. Each time consists of a large amount of material in an underground cave designed to shield them from [cosmic radiation]?.


See also solar neutrino problem, particle physics.

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Last edited November 22, 2001 5:20 am by Chenyu (diff)