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Under the neutron microscope

SNS / ORNL
This graphic shows components from various national labs that were put together
to create the $1.4 billion Spallation Neutron Source at Oak Ridge in Tennessee.


Technically speaking, the $1.4 billion Spallation Neutron Source is the world's most powerful accelerator-based source of neutrons - but the people who run the sprawling facility prefer to think of it as one of the highest-resolution microscopes ever built.

"You can think of this as a better, and better, and better digital camera," operations manager Frank Kornegay said last week, during a tour of the 80-acre site at Oak Ridge National Laboratory in Tennessee. "You can actually see electrons change state."

These snapshots aren't just for fun, however. The neutron-scattering patterns produced by the device show how materials ranging from industrial alloys to drug molecules are structured at the molecular level - and how they hold up under stressful conditions.

That could lead to better breeds of DVDs and other data storage media ... sturdier metals for engine parts ... more resilient skins for cars and airplanes ... new superconducting materials that work at higher temperatures ... plastics that stand up better to wear and tear, or degrade more easily when they're thrown away ... more effective medicines, and longer-lasting artificial joints.

Kornegay ushered me through the Spallation Neutron Source's industrial-style headquarters last week as if it were a fancy new home - and it is fancy and new, as nuclear physics facilities go. The place produced its first neutrons less than two years ago, and there are a couple of spots still open for beamline instruments.

Researchers put in proposals to use the facility, and business is brisk. Like the Hubble Space Telescope, the Spallation Neutron Source has a panel of experts who select which experiments get to use time on the machine. "We're oversubscribed by a factor of three," Kornegay said.

How it works
Neutron sources may not get as much press as particle accelerators such as the Tevatron and the Large Hadron Collider, but they have a lot of technology in common - and the practical applications are more obvious.

Lynn Freeny / ORNL
Samuel McKenzie examines a magnet used
to accelerate ions in the Spallation Neutron
Source, a sprawling facility at Oak Ridge
National Laboratory in Tennessee.


The front end of the Spallation Neutron Source is a 1,000-foot-long (330-meter-long) underground linear accelerator (or "linac") that blasts out negatively charged hydrogen ions. At the far end of the linac, the ions zoom through a foil that strips away the electrons, and the protons that remain are revved up in an accelerator ring to about 86 percent of the speed of light.

Pulses of protons - about a quadrillion protons per second - are fired at a container of liquid mercury. Each proton knocks about 20 neutrons off the mercury nuclei, much as one cue ball scatters the other balls lined up on a pool table. That's what's known as spallation.

The spalled, or scattered, neutrons are channeled through multiple beam lines to an array of instruments that works like a Swiss army knife for physics experiments: spectrometers and diffractometers over here, reflectometers and choppers over there. The "blades" of this all-purpose knife are spread out inside an industrial hall about as big as a college basketball gym.

"Each beam line is 12 million to 20 million bucks," Kornegay said.

How it's used
Inside the instruments, researchers place samples of the materials they want to study - for example, a new copper alloy that is being considered for use in engine radiators. When the neutron beam hits that alloy, the pattern of scattering can show exactly how the atoms of copper and other metals are lined up in the alloy. The researchers can read the patterns to find out if the composition of the alloy is what they were expecting - and figure out how to change the composition to make the material stronger.

Kornegay gave another example: Suppose a medical researcher wanted to encapsulate molecules of insulin in carbon nanotubes to create a new drug delivery system for diabetics. The neutron microscope could show whether or not the manufacturing process put the insulin in the right place - and whether or not the insulin is released as expected.

Researchers can monitor molecular changes in real time. "You can actually see proteins and enzymes in action," Kornegay said. "Nobody's wanted to put something alive in here, but I know that's coming."

The Spallation Neutron Source has already been recognized by the Guinness Book of World Records as the most powerful facility of its kind, wresting the title away from Britain's Rutherford Appleton Laboratory. The first peer-reviewed article based on research from the facility has just been published in Physical Review Letters. But for Kornegay and his colleagues, all this is only the beginning.

Oak Ridge is looking into ways to bring in research on a proprietary basis for a dollars-per-hour rate - which could attract business from some of the country's biggest industrial players. Kornegay expects the Spallation Nuclear Source to be in business for a long, long time: 40 years, to be exact.

"This is the microscope of the 21st century," he said.

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