The Sudbury Neutrino Observatory :

The Sudbury Neutrino Observatory (SNO) is a second generation water Cherenkov 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.

Physics :

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 Earth, as 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 an 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 is compelling evidence of neutrino mass. Non-zero neutrino mass is evidence for physics beyond 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.

Engineering :

The detector consists of a transparent acrylic sphere 12 m in diameter, supported from a deck structure by ten rope loops made of synthetic fiber. The sphere holds 1000 tones of heavy water. Surrounding the acrylic vessel is a geodesic structure 17.8 m in diameter made of stainless-steel struts and carrying 9438 inward-looking photo multiplier tubes. The barrel-shaped cavity is filled with purified light water to provide support and shielding from radioactivity in the rock.

The scientific program consists 3 phases with different detector configurations :

  1. Pure D2O - finished in June 2001
  2. Salt in D2O to enhance NC sensitivity - finished in June 2003
  3. Neutral Current Detectors (He-3 proportional counters) immersed in pure D2O to separately measure NC - in progress, due to finish in December 2006

Artist conception of the SNO detector


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 cavity excavated from the " 6800-foot" level of the mine.
At this depth only about 70 muons pass through the detector per day.

Location of SNO within the Creighton mine

SNO surface building

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 space.

And finally there is a lava lamp inside the detector control room to keep the operator entertained when the detector is running smoothly ! ;-) lava lamp

maintained by Scott Oser