Fall 2002 -- Vol. 20, No. 1

Sokol Spearheading Portion of $1.4-Billion Spallation-Neutron-Source Research Facility

Penn State Professor of Physics Paul Sokol is heading the scientific and construction programs of a cold-neutron-chopper spectrometer, which will be part of the United States Department of Energy’s $1.4-billion Spallation Neutron Source (SNS) project under construction on an 80-acre site at the Oak Ridge National Laboratory in Oak Ridge, Tennessee. It is the second biggest science project in the world right now, behind the International Space Station.

The Spallation Neutron Source is one of the largest scientific-facility construction projects that the United States has undertaken in several decades. When it is complete in 2006, the SNS – a collaboration of the Oak Ridge, Argonne, Lawrence Berkeley, Los Alamos, Brookhaven, and Jefferson national laboratories – will be the world’s premier facility for neutron research.

The SNS is an accelerator-based neutron source that will provide the most intense pulsed neutron beams in the world for scientific research and industrial development.

The SNS will fire an ion beam down its 30-meter-long accelerator tunnel toward a mercury target; a beam that, at 80 percent of the speed of light, could reach the moon in 1.5 seconds. The resulting protons will bombard the target, generating, or “spalling,” the neutrons for use in research. Spallation is akin to hitting a bucket of balls with a fastball. A few of the baseballs immediately pop out when the bucket is hit, while others rattle around in the bucket and then bounce out a few seconds later. When it happens in the SNS, spallation is a nuclear reaction in which the high-speed particle hits a heavy atomic nucleus. Upon impact, some neutrons are “spalled,” or knocked out, at high energies. Other neutrons are “boiled off” at lower energies as the bombarded nucleus heats up. For every proton that strikes the nucleus of an atom, 20 to 30 neutrons will pop out. A special instrument, the cold-neutron-chopper spectrometer works like the shutter on a camera to allow neutrons with desired energies to slip through. Researchers then study the pattern of the neutrons and the speed at which they move to try to solve some of the mysteries of basic science.

Sokol is leading an instrument-development team of more than 30 members, supplied by both universities and national laboratories, one of the first such collaborations for a Department of Energy instrument. Sokol’s Penn State team will split design duties with Argonne National Laboratory. Most of the actual instrument, which will be housed in a 30-foot-diameter, 25-foot-high building at Oak Ridge, will be built on Penn State’s University Park Campus. The design and construction efforts will involve as many as 30 Penn Staters.

“When this is built, it truly will be a world-class instrument with no equal, and Penn State will have access to a significant part of the beam time,” Sokol said. “We’ll be able to use our time for research on polymers, zeolites, diffusion studies, and magnetism. There are a whole series of experiments we want to do that just can’t be done anywhere in the world right now because instruments with high-enough flux sources and sensitive-enough detectors just don’t exist.”

The knowledge derived from neutron-scattering research has advanced basic science by revealing the crystal structures of atoms, individual molecules such as DNA, and solids. Scientists have used this knowledge to improve such everyday objects as credit cards, pocket calculators, compact discs, computer disks, magnetic recording tapes, shatter-proof windshields, adjustable car seats, and weather-forecasting satellites, and jet airplanes. The increased resolution of the new cold-neutron-chopper spectrometer, coupled with the broad range of energies and velocities it can handle, will allow it to tackle a broad variety of scientific problems in areas as diverse as biomaterials, polymers, cements, magnetic systems, geological systems, and quantum liquids. “It will allow us to address problems not possible at present,” Sokol said. “In addition, this spectrometer is complementary with other instruments planned for the SNS.”

For years, the United States has lagged behind in neutron-scattering research because of the relative weakness of its two spallation sources; one at Argonne National Laboratory in Chicago and the other at Los Alamos National Laboratory in New Mexico. The SNS will enable the United States to surpass Europe’s most intense source, which has a capacity of 150 kilowatts, or 150,000 watts. When it comes online, the SNS will dwarf Europe’s most intense source by a factor of 10, producing a power level of one megawatt, or 1 million watts.

Sokol said bringing the world’s most powerful spallation source online in the United States provides dual benefits. First, it allows scientists to conduct experiments on concepts about which they previously have only theorized. Second, it trains the next generation of scientists and researchers in the current and potential use of the facility.

Sokol said running a typical experiment averages anywhere from an hour to a day, with the experiment repeated several times to get it just right. The entire experiment, from setup to data collection, will last anywhere from a day to a week. In that short time, Sokol said, a gigabyte of data or more, enough to keep a person busy performing analysis for a month, will be accumulated during a typical experiment.

“It will be hard, even for a group of universities, to fully utilize this instrument all the time because we don’t have enough trained people to analyze the huge amount of data it’s going to generate. As part of the process, we’ll be developing a user community in the United States to take advantage of this instrument,” Sokol said. “Given that we’re so far behind the Europeans, the user community in the U.S. is not as well developed as it is in Europe. So, part of the money we’re getting is to fund the scientific research that will train postdocs and students so they’ll become the users of the future.”

Those “users of the future” will be learning an additional lesson – how to meticulously analyze mountains of data. “One of our major challenges will be learning how to deal with storing and analyzing the gigabytes of data we will collect from each experiment,” Sokol said.

The Spallation Neutron Source is expected to attract 1,000 to 2,000 scientists and engineers each year from universities, industries, and laboratories in the United States and around the world. The varied applications of neutron-scattering research will provide opportunities for experts in practically every scientific and technical field that contributes significantly to the United States economy. The research performed at the SNS is expected to strengthen the nation’s overall economy, energy security, and national security.

More information about the Spallation Neutron Source can be found online at <http://www.sns.gov >.

Andy Elder

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