SNO (image) American Chemical Society Caption Located two kilometers underground in a nickel mine in Ontario, the Sudbury Neutrino Observatory consists of a 12-meter-diameter acrylic vessel filled with 1,000 tons of ultrapure heavy water. It is surrounded by almost 10,000 light-sensitive photomultiplier tubes. Credit Minfang Yeh, Ph.D. Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.