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February 1997

Purdue lab helps solve mysteries, aids scientific studies

WEST LAFAYETTE, Ind. -- Purdue University researchers have combined chlorine, cosmic rays and a particle accelerator to help solve a mystery about the earth's ancient climate.

Scientists at the Purdue Rare Isotope Measurement Laboratory, or PRIME Lab, recently conducted experiments that helped scientists from New Mexico determine that 20,000 years ago, temperature fluctuations in the North Atlantic were part of global-scale climate variations.

That's just one example of how researchers across the country rely on PRIME Lab in a wide variety of investigations, from studying soil erosion and weather patterns to tracking aluminum absorption in humans to dating ancient glaciers, archaeological artifacts and meteorite falls.

PRIME Lab scientists specialize in accelerator mass spectrometry, a technique that uses a particle accelerator to "count" the number of rare atoms, called radioisotopes, of a given substance in a sample.

Researchers have used the technique and the Purdue facility to date geologic events such as ancient glacial activity in Wisconsin and California. Such investigations aid in the study of the past climate, and may shed light on future climatic patterns. Studies also are under way to trace how calcium, aluminum and cholesterol are absorbed in the body.

The lab also is used to date and determine the origin of meteorites that have fallen to earth, and to track the flow of pollutants in samples of air and ground water.

Radioisotopes have been used for many years to obtain information, but before accelerator mass spectrometry, accurate results were hard to achieve unless large quantities of the sample material were available. For accelerator mass spectrometry, scientists need a much smaller sample, as small as a milligram in some cases.

PRIME Lab was established in 1992 as one of three National Science Foundation research facilities for accelerator mass spectrometry. The lab also receives funding from the W.M. Keck Foundation of Los Angeles. The Web page for the lab is http://primelab.physics.purdue.edu/

Here's an example of a project the lab was recently involved with. Details of this study were published in November in the journal Science:

Researchers at the New Mexico Institute of Mining and Technology set out to determine whether cycles of extreme temperature fluctuations in Greenland late in the last ice age were part of global-scale climate variability or were restricted to the North Atlantic.

The New Mexico scientists gave researchers at PRIME Lab rock samples from four sites in the Sierra Nevada mountains in east-central California. The rocks had been gouged out of the mountains by advancing glaciers during the last ice age, and when the glaciers melted, the rocks were left behind in piles called moraines.

Rocks that previously had been buried in the mountain were left on top of the moraines, where they were exposed to the sky for the first time. They also were exposed to cosmic rays, high-energy, fast-moving nuclear particles from outer space.

"When cosmic rays hit the rock, they produced chlorine-36," says David Elmore, director of PRIME Lab and a professor of physics who analyzed the rocks. Chlorine-36 is a radioactive isotope of the element chlorine, which normally contains 18 or 20 neutrons. Chlorine-36 contains 19 neutrons, giving the isotope a slightly different mass.

"There was negligible chlorine-36 in this rock before it was exposed to the sky, but it accumulates over time as the rock is bombarded with cosmic rays," Elmore explains. "By counting how many chlorine-36 atoms were in a given mass of the sample, we could tell how long the rock had been exposed, and hence the approximate date when the glacier melted."

Elmore and colleague Pankaj Sharma determined that the rocks were exposed about 20,000 years ago, near the time of the North Atlantic temperature fluctuations, supporting the hypothesis that temperature fluctuations during the last ice age were part of global-scale climate variations.

CONTACTS: Elmore, (765) 494-6516; e-mail, elmore@physics.purdue.edu

Fred M. Phillips, New Mexico Institute of Mining and Technology, (505) 835-5540; e-mail, phillips@nmt.edu

Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu


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