The Sudbury Neutrino Observatory :
The Sudbury Neutrino Observatory (SNO) is a second
detector designed to determine whether the currently observed solar
neutrino deficit is a result of neutrino oscillations. The detector is
unique in its use of
D2O as a detection medium, permitting it to make a
model-independent test of the neutrino oscillation hypothesis by
comparison of the charged- and
neutral-current interaction rates.
The Sudbury Neutrino Observatory has been
constructed to study the
fundamental properties of neutrinos, in particular the mass and mixing
parameters. Neutrino oscillations between the electron-flavour neutrino
and another neutrino flavour have been proposed as an explanation of
the observed shortfall in the flux of solar neutrinos reaching the
compared with theoretical expectations. SNO has proven this hypothesis
by measuring the flux of electron type neutrinos which are produced in
the Sun via the charged current interaction (CC), and comparing it to
the flux of all active flavours of solar neutrinos detected on Earth in
appropriate energy interval via the neutral current (NC) and elastic
scattering (ES) reactions. SNO can also test the
oscillation hypothesis in the atmospheric neutrino
sector by measuring an angular distribution of arrival directions from
muon type neutrinos.
Observation of neutrino flavor transformation
evidence of neutrino mass. Non-zero neutrino mass is evidence for
the Standard Model of fundamental particle interactions.
Having resolved the long-standing solar
neutrino problem by showing that solar neutrinos do change flavour,
SNO's mission is now to study the oscillation mechanism itself in
detail and to search for any further surprises that neutrinos may have
in store for us.
The detector consists of a transparent acrylic
sphere 12 m in diameter,
supported from a deck structure by ten rope loops made of synthetic
The sphere holds 1000 tones of heavy water. Surrounding the acrylic
is a geodesic structure 17.8 m in diameter made of stainless-steel
and carrying 9438 inward-looking photo multiplier tubes. The
cavity is filled with purified light water to provide support and
from radioactivity in the rock.
The scientific program consists 3 phases with
different detector configurations :
- Pure D2O -
finished in June 2001
- Salt in D2O to enhance NC
sensitivity - finished in
- Neutral Current Detectors (He-3
proportional counters) immersed in pure D2O to separately
measure NC - in progress,
due to finish in December 2006
The SNO detector is located at 46° 28´
N, 81° 12´ W in the
INCO,Ltd., Creighton mine near Sudbury Ontario, Canada.
The center of the detector vessel is 2092 m below the surface in a
excavated from the " 6800-foot" level of the mine.
At this depth only about 70 muons pass through the detector per day.
During day time the detector is operated and
maintained from underground.
At night time detector operation takes place from surface where the
SNO-Collaboration maintains a building with a control room and office
And finally there is a lava
lamp inside the detector
control room to keep the operator entertained when the detector is
running smoothly ! ;-)