A gold mine for science

07/28/05

It is the deepest mine in the United States and was the site of the single largest gold deposit ever found in the Western Hemisphere. What has, for the past 125 years, been known as the Homestake gold mine, outside the town of Lead, in the Black Hills of South Dakota, could become the home of an enormous underground multipurpose national scientific laboratory.

The National Science Foundation has announced that the Homestake gold mine is one of two finalists in the competition to determine the future location of the Deep Underground Science and Engineering Laboratory (DUSEL). The Homestake underground lab proposal, which is being led by Kevin Lesko, a nuclear physicist with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), will receive a $500,000 grant from NSF to go forward with a conceptual design for DUSEL.

In all, eight sites across the United States and in Canada had been under consideration to be the future home of DUSEL. The other semi-finalist in the competition is the Henderson Mine, an active molybdenum mine in Empire, Colorado. The spokesperson for that collaboration is Chang Kee Jung, a nuclear physicist with the State University of New York at Stony Brook.

"The Homestake mine is a vast site capable of hosting a comprehensive suite of experiments in all major fields of science, including low background experiments and very large detectors in particle and nuclear physics, and multidisciplinary deep sub-surface studies in geosciences, geoengineering and microbiology," said Lesko. "Furthermore, with 375 miles of tunnels already carved, the Homestake site could be expanded over the next 30 years to accommodate an evolving scientific and outreach mission."

South Dakota governor Mike Rounds formed the Homestake Laboratory Conversion Project in 2003, with state funding authorized by the legislature, to enable the conversion of the abandoned gold mine to a deep laboratory. In response to the NSF announcement, the governor released the following statement.

"I am very happy that after an extensive scientific review process, we have again been selected as one of themost desirable locations for a deep underground science and engineering laboratory. This process has been a tremendous team effort that wouldn't have been possible if not for the scientific community having a vision for the future of science, and the Homestake Gold Corporation working with us to put together a land transfer plan, which was the first critical step in designing a deep underground science and engineering lab. This cooperative effort sends two clear messages to the National Science Foundation and the scientific community. First, that the best location in the United States for an underground science lab is available for development, and second, that South Dakota will do what it takes to make the lab a reality." The Need to Go Underground While the Homestake mine may have been emptied of all its precious metals, it represents pure gold in the future for a broad number of scientific investigations which must be carried out underground -- the deeper the better.

For example, a number of questions important to the fields of astrophysics and astronomy cannot be answered unless experiments are shielded from Cosmic rays and other background radiation by thousands of feet of rocks. Prominent among the experiments that require the ultra-low backgrounds realized at great depths are studies of the elusive, ghostlike sub-atomic particles known as neutrinos.

"Homestake will house the full spectrum of today's neutrino laboratories at one site," Lesko said, referring to such current underground facilities as the Sudbury Neutrino Observatory (SNO) in Canada, and the KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector) facility in Japan.

In recent years, experiments at SNO and KamLAND and other underground neutrino laboratories have confirmed that what was once thought to be a massless particle, does indeed have a small amount of mass. Like all great discoveries, this finding has raised new questions. A next generation of neutrino experiments at the much greater depths of the Homestake site should help provide answers.

"For example, detection of neutrinoless double beta decay, which can be done at Homestake, is the only way to determine whether neutrinos are their own anti-particle," Lesko said.

Other astrophysical research planned under the Homestake Underground Laboratory proposal include studies of gravity, and studies of dark matter, the mysterious form of matter that is invisible to our current means of detection, but whose ubiquitous presence throughout the universe has been indirectly confirmed.

Said Lesko, "Homestake could also host very large multipurpose physics detectors for detecting proton decay, one of the longest-lived unanswered questions in non-accelerator physics."

In studies closer to home, scientists will get a closer than ever look at the earth's crust and new opportunities for monitoring the movement of groundwater. They will also be able to examine the unique biochemistry of organisms that thrive under heat and pressure conditions which would be deadly to surface dwellers. Carbon sequestration efforts the idea of safely burying global warming gases like carbon dioxide underground should also receive a significant boost.

"Science will be the primary host," Lesko said. "Science will set the priorities and the facility will be developed to promote research, safety and the integrity of data."

Near and Long-term plans The Homestake Underground Laboratory proposal calls for a two-level facility; an upper level that will serve research operating from the surface to a depth of 4,850 feet. This is the depth at which nuclear physicist Raymond Davis, of Brookhaven National Laboratory (BNL), set up the world's first solar neutrino detector in 1965 and conducted the research that won him a share of the 2002 Nobel Prize in physics. Construction of the "4850 Lab," as envisioned in the NSF proposal, would entail modification of the existing site and preparation of new experimental chambers. The work is scheduled to begin next year. If all goes according to plan, experiments could begin at the 4850 level by 2007.

Construction would continue on a lower level facility which would descend to 8,000 feet. A large network of existing caverns, drifts, ramps and boreholes should enable the construction of this second level of experimental facilities to be accomplished at a relatively low cost.

"Over the next century and beyond, scientists will be confronted with many critical challenges requiring significant advances in our understanding of the underground environment," said Lesko. "To make meaningful progress towards understanding the science and engineering issues necessary for addressing topics such as energy resources, water resources and mineral resources, as well as hazardous waste disposal and carbon sequestration will require broad, multidisciplinary research projects that are ideally suited for an underground research laboratory."

Source: Eurekalert & others

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