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.