More than three years ago, a small group of physicists from across the nation went to the bottom of an idle northern Idaho silver mine searching for the "missing matter" of the universe.

They're still looking.The team is one of about a dozen groups worldwide trying to find evidence of "neutrinos," a building block of matter whose properties remain unknown.

The scientists want to know whether the subatomic particles have any weight. If proven, that fact could help explain whether the universe is collapsing.

"We're getting there," Howard Nicholson, a Massachusetts physicist with the project, said last week. "We've had a long, slow struggle."

Funded by federal grants, the researchers began their work in the early 1980s at the University of California-Berkeley. Tests measuring the radioactive decay of tiny sheets of molybdenum foil are conducted underground to keep cosmic rays from throwing off the results.

Since the underground work began, the team has faced troubles.

About six months ago, a ventilation shaft collapsed, Nicholson said. Though it's a stark reminder that the work is dangerous, the chief concern is that it exposed more rock and increased the amount of radon in the air.

Radon is produced by natural radiation from rock. It's a concern for the researchers because sensors can mistake it for radiation they are trying to measure.

Also, the team has had several members leave the project. Two scientists went into semi-retirement and another had a heart attack. Two students helping the project graduated.

"We're somewhat shorthanded," Nicholson said. "The plan is to get through with the people we have."

In addition to a 4,000-foot layer of earth, the apparatus the researchers use to measure the decay is encased in lead, wax and specially treated plastic.

The experiment normally operates unattended. Researchers take turns visiting the site every couple of weeks, checking on the equipment and collecting readings.

The first round of experiments ended without turning up evidence of neutrinos, Nicholson said.