Microprobe assists in identifying chemical elements of solidsBy Steve Koppes
The Electron Microprobe Laboratory has helped mining companies prospect for diamonds in Brazil and Canada, determine the composition of meteorites from deep space, and study a deadly disease in Turkey. And as one of the shared instrument facilities supported by the Office of the Vice President for Research and for Argonne National Laboratory, it is accepting new clients from across campus and from Argonne.
The microprobe can determine the type and amount of almost any chemical element found within a one-micron patch of sample, according to laboratory Director Ian Steele. A micron, one millionth of a meter, is just a small fraction the width of a human hair.
“You’ll see this machine periodically in CSI. They come up with a composition of the dirt the person walked in, or something like that,” he said.
The samples Steele receives are more likely to be a chunk of metal, a meteorite or a piece of bone. The vacuum condition under which the beam operates excludes the analysis of fluids and soft organic materials.
When the microprobe’s electron beam hits a sample, the electrons slow, generating X-rays from the sample itself. “The type and number of X-rays are proportional to the element and the amount of that element,” Steele explained.
The University, with partial support from the National Science Foundation, purchased the instrument in 1986 for $400,000. “There are probably a hundred of these at universities in the United States, and another hundred in industry,” Steele said. His clients in the past have included archaeologists from the University’s Oriental Institute, art historians from the Art Institute of Chicago, and scientists at universities in Illinois, Indiana and Wisconsin.
Lawrence Grossman, Professor in Geophysical Sciences, the Enrico Fermi Institute and the College, and Steven Simon, Senior Research Associate in Geophysical Sciences, rely heavily upon the electron microprobe to study meteorites. The chemical data locked within meteorite grains holds detailed information about how the sun and planets condensed from the gas cloud that formed the solar system.
The microprobe also helps mining companies locate diamond deposits. “They don’t actually look for diamonds. They look for minerals that are known to occur with diamonds,” Steele said. Armed with Steele’s data, the companies can follow the mineralogical trail of garnet, pyroxene, ilmenite and chromite washing downstream from some unknown source of diamonds.
From the University Hospitals, Steele has analyzed a variety of biomedical samples, including kidney stones, particles extracted from fluids or lodged in lung tissue. “You can analyze the particles embedded in the lung,” said Grossman, the faculty member who oversees the laboratory. The lung tissue itself consists of carbon, hydrogen and oxygen, all elements that the microprobe cannot detect.
Steele is currently working with a doctor who studies mesothelioma, a deadly disease of the lungs usually associated with asbestos exposure. But in a region of central Turkey called Cappodocia, the culprit is the mineral erionite.
“It’s the most carcinogenic mineral, according to the World Health Organization,” Steele said. “Hence, half the people in this area die of mesothelioma. In the average population it’s much less than 1 percent.”
The physicians who have studied mesothelioma in Cappodocia have learned that the disease has a genetic component. Some entire families fall victim to the disease, while families living next door escape unharmed. To further nail down what role genetics plays in the disease, Steele is helping to determine whether the erionite in the fatal rock dwellings differs in any way from the homes where healthy families live.
They all live in caves and houses made of volcanic rock erupted from a volcano 30 miles distant. “That’s the thing that keeps spewing out a rock called tuff,” Steele said. “It’s a relatively soft rock, easy to work with and hence used for house construction.”
Unfortunately, the tuff contains erionite grains that the local people breathe into their lungs. “These grains are typically like little needles, just like asbestos,” Steele said. “When you get mesothelioma, you die. There’s no cure.”
Fees for using the microprobe lab start at $300 a day, and that’s probably a bargain. “You can get huge amounts of information in a day,” Grossman said. For more information, call Steele at (773) 702-8109.