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Spallation Neutron Source Instrument

SNS: Seeing is Believing

by Theresa Pepin & Laura Buenning

Remember the old saying, “see no evil, hear no evil, speak no evil”? This prototypical perspective of polite, civilized society gets turned on its head in science and engineering. Ideally, researchers want to see, hear, and speak it all—both at a human scale and at scales that match the phenomena under investigation—in a time frame of their own choosing.

Then they want to make sense of it all as quickly as possible, tell the world what they’ve found, and move on to the next question.

Here in east Tennessee we are fortunate to live at a time and in a place where one of the largest and finest facilities for sensing and seeing finds its home.

The Spallation Neutron Source

Since 2006, the immense Spallation Neutron Source (SNS) facility at ORNL has lit a fire under scores of new ventures in neutron technology and custom instrument design.

This accelerator-based facility provides the most intense pulsed neutron beams in the world for scientific research and industrial development. Each year, it hosts hundreds of researchers from universities, national laboratories, and industry, who conduct basic and applied research and development using neutrons.

With the presence of this invaluable laboratory facility on our home turf, it is worth the time to learn more about neutrons and their use in experiments that probe and peer into all kinds of samples.

Why Neutrons?

In contrast with more familiar X-rays, whose imaging is based on material density, neutrons reveal structure and function based on the different elements in a material. X-ray (photon) and electron beams interact with electrons, while neutrons interact primarily with atomic nuclei.

Neutrons are non-invasive and nondestructive probes; they can deeply penetrate but do not damage samples; they can precisely locate “lighter” atoms such as hydrogen or oxygen, for example, among “heavy” atoms such as mercury or other metals; they can track molecular vibrations and movements of a protein; they are impervious to extreme environmental conditions and have both particle- and wave-like properties.

Upon penetration of a given sample, the neutrons’ particle/wave properties make it possible to use a technique called neutron scattering whereby scientists count scattered neutrons, measure their energies and the angles at which they scatter, and map their final positions. Neutrons can also be used to create two- and three-dimensional images of the distribution of light elements in a material (known as neutron imaging).

Taken together these methods can reveal the structure and behavior of materials over multiple scales.

Neutron technology is a powerful cutting-edge technique in the arsenal of scientific tools needed to probe materials and understand the full range of structural properties.

JDRD researchers seek to see—accurately and productively—in a wide range of ways, over scales never before imagined. Joint Directed Research and Development funding allows them to take that challenge to a new level.