Geologists at the University of California, Davis, are using neutron beams from a nuclear reactor to see inside rocks. The method could be used to look for traces of life in rocks from Mars or very ancient rocks from the Earth.
"Normally, we'd make a three-dimensional image by cutting the rock in slices. With this method, we can do it without destroying the rock," said 51³Ô¹ÏºÚÁÏ Davis geology professor Charles Lesher.
Researcher Martin Wilding, geology assistant professor Dawn Sumner and Lesher have already used the method, called neutron tomography, to find bacteria living inside rocks collected in the Mars-like environment of Antarctica's dry valleys and Israel's Negev desert. They're also using it to study the structure of volcanic rocks and glasses, and of "black smoker" chimneys collected from the deep ocean floor.
Neutron tomography could also be used for biology experiments, such as filming water movement inside plants, Wilding said.
"We're just scratching the surface of what we can do," he said.
Neutrons are very sensitive to water and light elements such as the hydrogen and carbon, which are major components of living things. But they can pass right through a steel container. In contrast, water and most living tissue are fairly transparent to X-rays, but X-rays are stopped by heavier elements. That means that neutron beams can be used to scan a Martian rock for traces of life even while it is sealed in a metal container.
The process is comparable to a medical CT (computed tomography) scan with X-rays. The sample rotates in the neutron beam and a series of pictures are taken with a digital camera system. These two-dimensional images are reconstructed, using the same equations used for CT scans, into a series of "slices" through the sample. These slices can also be made into a three-dimensional image.
The neutron beam is generated by the research reactor at 51³Ô¹ÏºÚÁÏ Davis' McClellan Nuclear Radiation Center. The reactor was built in 1990 by the U.S. Air Force to check for corrosion in aircraft components. It was transferred to 51³Ô¹ÏºÚÁÏ Davis in 2001.
Note: Quicktime movies of bacteria within a rock and of geology samples are available. Contact Andy Fell for details.
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Andy Fell, Research news (emphasis: biological and physical sciences, and engineering), 530-752-4533, ahfell@ucdavis.edu