The University Record, April 23, 1996

New geochemistry lab features rare spectrometer

Chris Ballentine, assistant research scientist in geological sciences, calibrates one of three noble gas mass spectrometers in the renovated Radiogenic Isotope Geochemistry Laboratory.

Photo by Bob Kalmbach


By Sally Pobojewski
News and Information Services

The Department of Geological Sciences celebrated the grand opening of its expanded Radiogenic Isotope Geochemistry Laboratory yesterday with an open house for faculty, students and distinguished guests.

Vice President for Research Homer A. Neal dedicated the showpiece of the new lab---a $900,000 multiple collector inductively-coupled plasma magnetic sector mass spectrometer (MC-ICPMS) manufactured in the United Kingdom. Mass spectrometers are a common instrument in science labs across campus, but this one is truly one-of-a-kind, according to Alexander N. Halliday, professor of geological sciences and director of the laboratory.

"The U-M Radiogenic Isotope Geochemistry Laboratory was the first to use a prototype of this new type of mass spectrometer," Halliday said. "At this time, there is still only one other like it in the United States."

Halliday and his research colleagues measure relative amounts of specific isotopes in rocks and sediment to reconstruct the timing and chronology of events occurring early in Earth's history. The MC-ICPMS system has several features that make it particularly well-suited to this type of research, Halliday explained.

Scientists use mass spectrometers to measure the proportions of different isotopes of an element in a sample by separating atoms according to their atomic mass and sorting them in separate piles from "heaviest" to "lightest." The procedure only works, however, when the chemical elements are ionized or carry an electrical charge.

"Some elements in the periodic table ionize more easily than others," Halliday explained. "Many of the elements we use in our research---such as tungsten, platinum and hafnium---are difficult to ionize. This new mass spectrometer features a high-efficiency argon plasma source capable of ionizing nearly all elements. It allows us to measure precise isotopic composit ions of elements which are difficult to ionize, even when these elements are present only in very small amounts.

"In addition, we can now make isotopic measurements directly from a solid sample with higher precision than has ever before been possible by using an ultraviolet wavelength laser to ablate or remove particles which get wafted into the plasma," Halliday said.

Halliday said the increased precision and efficiency of the new mass spectrometer system will allow his research team to expand their work into new areas---including cosmochemistry, which uses the composition of meteorites and space material to help understand how the solar system was formed.

Funds to purchase the MC-ICPMS system were provided by the National Science Foundation; the College of Engineering; College of Literature, Science, and the Arts; the Office of the Vice President for Research; and the Departments of Geological Scie nces and Nuclear Engineering.