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[NEWS from the Office of the Vice Provost]

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At Cornell

CHESS
Scientists’ High Energy X-ray Tool

The Nature of X-rays

Donald Bilderback

Anyone who has visited a dentist’s office or hospital knows that invisible x-rays can go right through us and produce shadowy images of our teeth or bones. These common images already portray quite a bit about the nature of x-rays: they are a high energy light that can penetrate deeply into matter; they can be preferentially absorbed by dense matter (like bone); and they make fuzzy grayscale images on film.

How Small is Small?

These are just a few of the many properties of x-rays that bring hundreds of scientists—chemists, biologists, physicists, environmentalists, and art historians—to CHESS each year in order to peer inside all sorts of materials. Unlike medical x-ray sources, the CHESS x-ray beams produced by the CESR synchrotron are small, laser-like beams with intensities hundreds of millions of times brighter than radiograph machines. These small, intense beams are perfect for examining extremely small specimens. The typical sample brought to the synchrotron is a millimeter in size, and many are so small, they cannot be seen by eye. In addition, high energy x-rays have very small wavelengths, typically a tenth of a nanometer or smaller, a length commonly referred to as the Angstrom unit. These wavelengths are 1,000 times smaller than visible light. Because they are so small, x-rays are one of the few tools perfectly adapted to peering inside almost anything to “see” actual arrangements of atoms and molecules.

From Concrete to DNA

Just about anything can be studied with x-rays—from concrete to DNA. Hundreds of measurement techniques use x-rays. Some are as simple as x-ray absorption (like the medical radiograph), and others are more complicated procedures that measure tiny changes as x-rays pass through a sample.

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“The CHESS staff hosts 400 to 600 scientists each year—chemists, biologists, physicists, environmentalists, and art historians—who want to peer inside all sorts of materials.”