The Sudbury Neutrino Observatory (SNO), a 1000 ton heavy water
Cherenkov detector under
construction in INCO's Creighton mine near Sudbury, Ontario (Canada)
Neutrino detectors
Neutrino interactions
with matter are extremely
rare, making detection difficult.
Neutrino detectors are typically large tanks filled with a
fluid that reacts to the passage of neutrinos.
To take advantage
of the high flux of neutrinos passing through the Earth
(billions per second),
neutrino detectors are made as large as possible. The
larger the detector, the more neutrinos can be
measured in a reasonable amount of time.
For example the
Super-Kamionkande
device under construction in Japan is designed to detect about
11,000 neutrinos per year.
Early neutrino detectors were filled with perchloroethane
(a type of cleaning fluid containing chlorine).
A portion of the chlorine is isotope 37
(17 protons and 20 neutrons), which
can react with neutrinos to produce
Argon-37 (18 protons and 19 neutrons).
The amount of Argon-37 created is then used to
measure the neutrino flux.
Another fluid used for neutrino detection is water.
Neutrino interactions in water produce the
Cherenkov effect.
Light emitted in this manner is detected
by sensitive detectors surrounding the fluid.
Cosmic rays can cause unwanted signals in these detectors.
To avoid this problem, the detectors are put deep
underground, so that layers of rock can shield
the detector from cosmic rays.
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