Upgrades At NIST Cold Neutron Research Facility Benefit Advanced Materials Research

Upgrades at the Cold Neutron Research Facility of the Commerce Department's National Institute of Standards and Technology in Gaithersburg, Md., are enabling scientists to better understand advanced materials for more powerful computers, more efficient automobiles and more effective catalysts.

Recently completed upgrades at the CNRF are providing cold neutron beams up to nine times more intense than those previously available at the facility. Researchers use cold neutrons to see structure, composition and dynamic properties of materials, which can not be determined any other way. Neutrons are more penetrating than electron beams or X-rays, which also are used to probe materials. Another advantage of neutron beams is that samples remain undamaged when neutrons pass through them. In addition to upgrades to the facilities' cold source and heat exchangers, new experimental stations have been added and others improved.

Neutron research facilities have been available at NIST since 1969 when NIST (then the National Bureau of Standards) dedicated its 20 megawatt nuclear reactor. The NIST Cold Neutron Research Facility, added in 1990, significantly improved research facilities for U.S. scientists working in materials science, chemistry, physics and biology.

With its most recently completed improvements, the NIST Cold Neutron Research Facility can meet as broad a range of research needs as any other neutron research facility in the world. Improvements to the facility were made during a 16-month shutdown of the NIST research reactor.

Fission reactions in the reactor liberate large numbers of very energetic, high- speed neutrons. These neutrons quickly slow and cool as they pass through a newly installed chamber of liquid hydrogen (-253 degrees Celsius). This improved cold source, with the increase of reactor power from 15 to 20 megawatts, has increased the intensity of neutrons available at all experimental stations in the Cold Neutron Research Facility up to nine times.

During the reactor shutdown, scientists added and improved several instrument stations in the Cold Neutron Research Facility Guide Hall.

The two new instruments are:

• a neutron reflectometer, which scientists use to study surface and interfaces of different layers in a wide variety of materials. The instrument gathers information on samples by glancing a fine beam of neutrons off their surface, the same way a stone thrown at a low angle can skip off water.
• a neutron interferometer for many materials science and fundamental physics experiments. A neutron interferometer splits, then recombines neutron waves. This gives the instrument its unique ability to experimentally access the phase of neutron waves. Phase measurements are used to study the magnetic, nuclear and structural properties of materials, as well as fundamental questions in quantum physics.

Two other experimental stations were improved significantly during the reactor shutdown:

• a 30-meter small-angle neutron scattering, or SANS, instrument is better able to measure very small scale structures and has new automated controls. SANS instruments are particularly good at revealing properties of polymers, the porosity of ceramics and characteristics of colloids on a scale as small as a billionth of a meter. Biologists use the SANS instrument to determine structures of proteins that cannot be crystallized or effectively examined with X-rays.
• a spin-polarized inelastic neutron scattering, or SPINS, spectrometer is now fully equipped for polarization analysis and is capable of very high resolution studies of the structure and atomic-scale properties of magnetic and superconducting materials.

Additional experimental stations now under construction include:

• a backscattering spectrometer, which will measure motion of atoms in materials. When it becomes operational, it will chart both the velocity and direction of atoms in a sample, which are critical, for example, to its chemical or conducting properties.
• a spin-echo spectrometer, which will be used to probe large-scale motions of polymer chains, biological molecules and other advanced materials. The instrument detects molecular or magnetic motions within a sample by measuring the change in the rotation rate of a neutron spin after it scatters from a sample.
• an extremely versatile disk-chopper time-of-flight spectrometer, which will be used to reveal the vibrations and rotations of molecules in advanced materials. It will help scientists study molecular processes in catalysts and proteins,as well as the diffusion of hydrogen and other atoms in metals and batteries.
• a double-axis neutron diffractometer, a new thermal neutron instrument, is expected to be operational in early 1996. Scientists will use it to measure interatomic spacings with very high accuracy. Such measurements reveal how manufacturing processes produce residual stress in materials, which greatly affect their performance and durability.

When fully instrumented, the Cold Neutron Research Facility will include 15 experimental stations. Five of these will be supported and operated by participating research teams with industrial, government and academic members. In exchange for maintaining their stations, the participating research teams will have exclusive use of three-quarters of the available instrument time. The remaining research time will be allocated to qualified U.S. researchers through a competitive selection process. Two-thirds of research time on the 10 NIST-maintained instruments will be available to U.S. researchers.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.