Qualla: Sudbury Neutrino Observatory

Sudbury Neutrino Observatory: Introduction

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit User:Boardhead, CC0. Somewhere beneath your feet, if you are flying over Greater Sudbury, Ontario, a Nobel Prize was won in darkness. Two thousand one hundred meters below the surface, inside Vale's Creighton Mine, physicists constructed the Sudbury Neutrino Observatory -- a spherical detector lined with 9,600 photomultiplier tubes, watching a thousand tonnes of heavy water for the faintest flashes of blue light. The light came from neutrinos, ghost particles streaming from the core of the sun, passing through the Earth almost without a trace. Almost. Between May 1999 and November 2006, SNO caught enough of those traces to solve a mystery that had haunted physics for forty years. The sun was not broken. The neutrinos were changing.

Image: User:Boardhead | CC0

Sudbury Neutrino Observatory: The Missing Neutrinos

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit NASA, ESA, J. Hester and A. Loll (Arizona State University), Public domain. Since the 1960s, every detector on Earth had counted roughly a third to a half fewer neutrinos arriving from the sun than the Standard Solar Model predicted. The discrepancy became known as the solar neutrino problem, and it persisted for decades. Either the models of how the sun...

Image: NASA, ESA, J. Hester and A. Loll (Arizona State University) | Public domain

Sudbury Neutrino Observatory: Heavy Water and Deep Rock

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit NASA, ESA, J. Hester and A. Loll (Arizona State University), Public domain. In 1984, physicist Herb Chen of the University of California at Irvine proposed a detector using heavy water, in which hydrogen atoms carry an extra neutron. Heavy water enabled two distinct detection reactions: one sensitive only to electron neutrinos, the other sensitive to all...

Image: NASA, ESA, J. Hester and A. Loll (Arizona State University) | Public domain

Sudbury Neutrino Observatory: A Cathedral of Light

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit Boardhead at English Wikipedia, CC BY-SA 3.0. The finished detector was an engineering marvel. A 12-meter acrylic vessel held the heavy water, surrounded by a cavity filled with ordinary water for buoyancy and radiation shielding. Approximately 9,600 photomultiplier tubes, mounted on a geodesic sphere, watched for the tellta...

Image: Boardhead at English Wikipedia | CC BY-SA 3.0

Sudbury Neutrino Observatory: Neutrinos Change Their Stripes

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit NASA, ESA, J. Hester and A. Loll (Arizona State University), Public domain. On June 18, 2001, SNO published its first results: clear evidence that solar neutrinos oscillate, transforming from one flavor to another during their journey from the sun. The total neutrino flux across all three flavors matched the Standard Solar Model's predictions. The sun wa...

Image: NASA, ESA, J. Hester and A. Loll (Arizona State University) | Public domain

Sudbury Neutrino Observatory: Nobel Recognition

Mon, 23 Feb 2026 00:00:00 GMT

Photo credit NASA, ESA, J. Hester and A. Loll (Arizona State University), Public domain. In 2015, the Nobel Prize in Physics was awarded jointly to SNO's director, Arthur B. McDonald, and Takaaki Kajita of Super-Kamiokande for the discovery of neutrino oscillation. The SNO team had already received the inaugural John C. Polanyi Award in 2006 and the 2016 Fundamental ...

Image: NASA, ESA, J. Hester and A. Loll (Arizona State University) | Public domain