The great neutrino hunt

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Creatures in strange places

Image of gold from State of California website.

The Homestake mine was carved into the earth of Lead, South Dakota, more than a century ago. Original map from Department of Energy.

This week, a team of top scientists will submit the final proposal for the creation of a vast underground laboratory inside a South Dakota gold mine. It is a $281 million scheme that has been several years in the making.

Meanwhile, the massive machinery that kept the mine from flooding for 125 years has gone silent. As a result, water rises slowly but steadily from the bottom of the 8,000-foot cavity.

A waterlogged mine would be useless as a research vessel, but clearing it out would take years and millions of dollars. It would also stall the project that scientists are already restless to get moving.

For now, the Homestake gold mine of Lead, S.D., is mostly dry. So for at least one architect of the proposal, the proverbial glass is half full. "Our fondest hope is that [the proposal] will go through before water reaches 7400 foot level, where we do our major work," says University of Washington physicist Wick Haxton.

Homestake is an ideal site for the national lab, Haxton says. It is the deepest mine in the US, at the site of the largest single deposit of gold ever found in the Western Hemisphere. Many American scientists who need a quiet underground environment now travel abroad to use active mines in in Italy, Japan, Sweden, and South Africa. But converting the old South Dakota mine into a lab would allow them to work closer to home, in an environment tailored for their research.

Delicate particle physics experiments, for example, use instruments that are so sensitive to environmental forces -- especially the cosmic radiation that soaks the atmosphere -- that only deep underground places are sufficiently shielded.

In fact, it was inside the Homestake mine that physicist Raymond Davis first detected neutrinos from the sun in 1965. Neutrinos are the tiny (so tiny, that for decades scientists thought they had no mass at all), elusive particles that stream from the thermonuclear reactions at the center of the sun.

Neutrinos are hard to detect because they zip through matter unnoticeably; thousands are whizzing through you at any moment. Because the trek through space causes only subtle changes in neutrinos, they carry loads of information about the core of the stars where they are born.

To detect the ghost-like particles, Davis built a tank filled with 378,000 liters of perchloroethylene (cleaning fluid) inside the mine. Neutrinos passing through the tank would change some of the chlorine atoms to argon, he guessed. When he collected argon, Davis had in effect "seen" neutrinos from the sun for the first time.

Davis won the Nobel Prize for his work just last year, for his work just last year, when researchers showed that his results showed that neutrinos have a mass. And his research was the seed for decades more neutrino research, much of which has been conducted at Homestake.

This 1966 photo shows the construction of Ray Davis' neutrino-capturing tank in the Homestake gold mine. The tank, 20 feet wide and 48 feet long, held 100,000 gallons of cleaning fluid nearly 5,000 feet underground. Photo: Brookhaven National Laboratory.

Going down under
At more than one and a half miles down, the Homestake mine would be the world's deepest underground lab. And 500 miles of already-carved tunnels would provide plenty of space, and essential ventilation, for long-term, sensitive experiments.

The Homestake Company owned the mine for more than a hundred years, often taking pains to aid the scientific pursuits inside its caverns. But the mine was picked clean of precious metals by 2000, when Homestake was acquired by Barrick Gold Corp. of Toronto.

Barrick offered to donate the mine to the state of South Dakota soon after company executives learned it was under consideration for the national laboratory project. But the process has been full of legal hurdles. Barrick has been reluctant to hand over the lab until the state of South Dakota can guarantee the company won't be held liable for any safety or environmental hazards that may appear later.

And the company decided not to bear the cost (hundreds of thousands of dollars a month) to keep the mine water-free until the process is seen through. Barrick and South Dakota officials have released public statements saying the mine could be dried again if the proposal pushes through Congress.

Haxton, however, says it would cost would cost as much at $40 million to drain the mine and fix the water damage, if the flooding continues for long.

Vincent Borg, a spokesman for Barrick Gold, tells The Why Files that the company supports the lab and is eager to donate the mine. If there has been an impasse in the transfer, Borg remains mum. "We're committed to working with the state to facilitate the donation," he says. Shutting down the pumps was a standard part of the closing process that had already begun when Barrick acquired the mine three years ago.

According to Borg, it would take 25 years for Homestake to flood. It's more cost effective to pump it dry once the proposal has passed instead of continuing to clear it -- at a cost of hundreds of thousands of dollars a month -- as the proposal waits for funding.

All that glitters is not gold
The lab would be a fine setting for research into science's great infinities: the universe and the particle. And it is a ready-made observatory for those who study how the rocks of the Earth's crust -- and the minute creatures that live among them -- grow and change.

"It's not exactly the space program, but it has some of same elements," says Haxton. "It's learning from a very new environment that may be of very useful to many different areas of science."

Capturing and studying neutrinos on Earth will help scientists understand how stars are born. This image shows the early formation of a neutron star as it radiates billions of neutrinos per second.Image: Oak Ridge National Laboratory.

The bid to construct a massive underground lab is "really the only opportunity scientists have had to develop such a concept for multidisciplinary research," says Tullis Onstott, a geoscientist at Princeton University.

For one, physicists hope to build a super-sensitive neutrino detector inside the lab. It would allow them to expand on recent experiments in Japan and Canada that recently measured the mass of the slight particles. Neutrino research could also explain the secrets of the mysterious substance that pervades the universe known as dark matter, and reveal why the universe has any matter at all, says Haxton.

Working deep underground might also allow scientists to spot underground nuclear explosions (the kind that are likely when, say, another country wants to keep its nuclear weapon development program a secret). Such explosions release small amounts of radioactive xenon, says Haxton. Particles could be collected from the air near suspected test sites, and later be tested underground to reveal whether, in fact, there had been a nuclear explosion.

The lab will also be a new window on the lives of the hardiest microbes. Those that can survive the heat and pressure deep in the crust are probably much like those that survived the hot, soupy conditions of the early Earth. What scientists learn from the first group could speak volumes about the latter. Tullis Onstott envisions researchers boring holes into the mine's fractures to find rarely seen bacteria. "It's a capability that just doesn't exist right now, at all, anywhere," he says.

Looking for these tiny organisms could help scientists refine the way they look for life on other planets. One eventual goal is to better understand how to detect life's signatures in rock fractures at great depth. It would be valuable preparation for a subsurface drilling platform looking at life on Mars, Onstott says.

For geologists, the lab would provide a rare look at the Earth's crust. Most studies of deep rock now rely on core samples -- imagine drilling a small hole in a wall, and trying to understand the wall by looking at the pieces of plaster and the hole. Observing the guts of an underground lab the size of Homestake would be more like a slamming a refrigerator through the wall and walking on in for a look around. What's more, most underground experiments occur in granite mines built to store radioactive waste. Since most of the Earth's crust is made of striated, chunky metamorphic rock -- the kind Homestake was carved into -- a lab inside Homestake would provide a more natural setting.

Atmospheric scientists plan to study how carbon dioxide -- the menacing gas largely responsible for global warming -- is soaked up underground. Someday, scientists could thrust excess CO2 underground, where it could be naturally converted into basic elements.

The underground lab could also help scientists understand how water flows around at great depths. Such research could help scientists manage drinking and irrigation water and develop safer hazardous waste disposal sites.

The lab would also offer a show of the natural bending and straining of underground rocks. By watching carefully, earth scientists hope to better understand how earthquakes form and what seismic signatures to look for before they strike.

For now, the proposal is in the hands of a National Science Foundation panel of experts. After the NSF review, the bid will go to the White House for funding. If all goes well, Homestake could be drained and primed for stardom among mega-labs within a year.

By all accounts, it would be ... well ... a gold mine.

-- Sarah Goforth

Bibliography
"Pumping row erodes hope for underground lab," Geoff Brumfiel, Nature, 12 June 2003.

"'Mile-deep club' of researchers sets sights on disused gold mine," Geoff Brumfiel, Nature 26 September 2002.

"A world-class lab, 8,000 feet underground," Peter Spotts, Christian Science Monitor, 22 June 2001.

"Competition heats up for underground U.S. lab," David Malakoff, Science, 28 March 2003.

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