Lens gets X rays to a point.

Researchers have designed a simple, inexpensive lens for X rays that can focus a high-energy beam down to a spot just 8 micrometers wide. Such concentrated X rays could be used to probe the structure of individual grains of materials or to make images of single cells.

The compound lens, described in the Nov. 7 Nature, is a block of aluminum with a row of 30 cylindrical holes, each 0.6 millimeter in diameter, bored into it. The slivers of metal between the holes form a series of concave strips that can act as simple lenses. An X-ray beam directed at the end of the block passes through each strip of aluminum. Each successive strip bends the X ray slightly, gradually focusing the beam to a point.

This device-unlike those using mirrors, diffractive lenses, or glass tubes to collimate beams (SN: 6/27/92, p. 422)-actually refracts X rays, just as a glass lens refracts visible light. Because most materials bend X rays only slightly, a single lens is not practical. The multiple-lens design overcomes that limitation.

Other low-density materials could work, but "aluminum is the most suitable," says coauthor Anatoly Snigirev of the European Synchrotron Radiation Facility in Grenoble, France. "It has relatively low absorption for hard X rays, and you can easily drill holes into it."