SNO Update: Lab Completes Its Part of the Observatory Construction

March 6, 1998

By Monica Friedlander, [email protected]

On January 23, Kevin Lesko breathed a huge sigh of relief. The project leader for Berkeley Lab's part of the SNO experiment watched as the last of the 761 panels housing the experiment's 9,500 photomultiplier tubes was installed into SNO's support structure -- a stainless steel geodesic sphere designed by the Lab's Engineering Division. "Not a single tube was broken," said Lesko.

The observatory's centerpiece is covered with panels housing almost 10,000 photomultiplier tubes. The geodesic sphere and the panels were constructed by Berkeley Lab. | Photos by Roy Kaltschmidt

The support structure, which surrounds the experiment's acrylic vessel, is Berkeley Lab's principal hardware contribution to the Sudbury Neutrino Observatory -- a state-of-the-art underground laboratory built two kilometers under solid rock in a nickel mine in Ontario, Canada. Its goal: to study the nature of the neutrino, the tiny nuclear particle that physicists suspect could hold the key to determining the nature of dark matter and missing matter in the universe.

"Completing Berkeley Lab's component marks a big accomplishment, a big milestone," said Lesko, who spent more than five weeks in Sudbury in December and January overseeing the final construction.

In February the first heavy water shipment, on loan from the Canadian government, was shipped underground and the work of connecting the PMTs to the electronics was started The entire experiment will be submerged in 7800 tons of shielding water. SNO's unique capability to measure both the neutral and charged current signals, as well as the spectra shapes, provides the SNO collaboration unambiguous signals of neutrino oscillations. Berkeley Lab scientists Yuen-dat Chan, Colin Okada and Anett Schuelke are on-site working on detector calibration and data acquisition. In another four to six months the vessel will be filled with heavy water (approximately 350 tank cars' worth) and SNO will start collecting solar neutrino data.

"The physics community is waiting for SNO measurements to answer questions about neutrino mass and oscillations and the long standing solar neutrino problem," Lesko said. If all goes well, he estimates the answers can be expected in about two years.

Meanwhile, the official opening ceremony for SNO is scheduled for April 29. In addition to the various heads of state and other officials from the participating nations, a featured guest will be Stephen Hawking, the world-renowned cosmologist and author of the best-selling book "A Brief History of Time."

The design, engineering, fabrication and installation of the support structure was a collaboration between the Engineering and Nuclear Science Divisions. In addition to NSD's Kevin Lesko, team members included Peter Purgalis, the project engineer; mechanical engineers Yoichi Kajiyama and Steve Lundgren; designers David Beck, Fred Dycus, and Gary Koehler; installation supervisors Milt Moebus, Steve Turner and Joe Gonzalez; physicists Yuen-dat Chan, Eric Norman, Bob Stokstad, Colin Okada, and Anett Schuelke; and graduate student Mike Dragowsky. "The continued support I received from the Berkeley Lab engineers, in particular Yoichi Kajiyama, permitted us to install the PMT array within the original budget and duration estimates," Lesko said.

The international collaboration involves the participation of 70 scientists from the. U.S., Canada and Great Britain.

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