By Karen C. Fox
Article originally from American Chemistry magazine.

Nestled in the thickly wooded hills of Eastern Tennessee, a giant laboratory is taking shape. The sound of construction has been ringing out for six years at Oak Ridge National Labs, and its new facility is almost ready to be shared with the rest of the world. By summer of 2006, the biggest scientific lab this country has built in over a decade will go online.

The machine that will be housed here is called the Spallation Neutron Source (SNS) and it will make use of neutron beams to map the atomic structure of anything from semiconductors to Plexiglas® to rubber. The Department of Energy (DOE) has invested $1.4 billion into the facility in an attempt to bring neutron science up to the appeal it has in places like Europe.

A commitment to science
Government labs and industry research are not always automatic bedfellows. The U.S. only offers their facilities free to those doing peer-reviewed, non-proprietary research and seeks payment from those doing proprietary work. The government-run SNS offers many advantages to the chemical industry, which relies heavily on fundamental science. Early basic research into something as simple as how atoms and molecules work has led to new technologies such as cutting-edge medical imaging techniques, the understanding of electro-magnetic properties to make computer chips, and the creation of all manner of new materials. The chemical industry has had a longstanding commitment to basic science, also known as “curiosity-driven,” or “discovery” science. From materials used in airbags to coatings on airplanes, improvements in the making of these products is due partly to a deeper understanding of molecular structure.

Even if everyone agrees on the importance of studying such basic structures, figuring out how to do so is not always straightforward. Using neutrons to determine atom position is only one technique needed to attack any given problem. The high cost involved with imaging makes it the kind of tool only a wealthy government can provide. Therefore, neutron science is an ideal starting point.

“It is always fun, and frankly a privilege, to be able to go and use the national facilities,” says Alan Nakatani, a research scientist with Rohm and Haas, in Pa. “It is one of the rewarding aspects of our jobs here. It gets you out of the standard lab environment, and gets you into places you do not normally have a lot of opportunity to go to.”

Neutrons go neutral
The SNS is an example of how basic research can turn into fascinating technologies. The first physics accelerators built in the U.S. in the first half of the 20th century were used solely to smash atoms together and study their innards. Soon, researchers realized the intense x-ray radiation produced by the speeding particles in the accelerators could be used to map the molecules in crystals. By bouncing x-rays off a crystal and recording the ways in which the molecules scatter, scientists are able to precisely map its inner structure.

Neutron beams can be used to map structure in the same fashion, except they ‘see’ slightly different things. They are much better at spotting light elements like hydrogen and oxygen––a plus for the plastics industry, since polymers heavily incorporate these elements. However, neutron beams are weak compared to the imaging strength of x-rays. Imagine trying to read by candlelight as compared to the bright rays of the sun. The power to see clearly, especially on a small sample, is just not there.

Consequently, neutron research in the U.S. has lagged behind other countries. There are some neutron source facilities at Brookhaven, the National Institute of Standards and Technology (NIST), and Los Alamos, yet none come close to the power of the strongest neutron source in the world: ISIS in the United Kingdom, the world’s largest neutron source, located at Rutherford Appleton Laboratory, near Oxford. ISIS supports an international community of around 1,600 scientists, who use neutrons for research in physics, chemistry, materials science, geology, engineering, and biology. However, the SNS will provide beams five to 10 times stronger than ISIS, ushering in––the DOE hopes––a new era for the field.

Jack Rush, who retired in early 2005 as the director of NIST’s neutron scattering program, has worked with some 40 different industrial partners including Rohm and Haas, ExxonMobil, Dupont, and Dow, and has seen firsthand how the chemical industry has benefited. Tires, for example, have been made more durable and more flexible by using neutrons to analyze new polymers. ExxonMobil depended heavily on neutrons to develop a next generation engine oil additive for trucks. Dupont has used neutron imaging to study magnetic oxides for use in magnetic devices.

In the future, neutrons will bring the biggest advantages to two particular areas for the chemical industry, says Rush, “catalysts and soft matter.” Catalysts are substances used to initiate any chemical process. Improved catalysts, many of which incorporate oxygen and silicon, lead to more efficient, environmentally cleaner systems. Soft matter, on the other hand, covers a wide range of materials including rubber, plastics, and soaps––anything containing organic molecules, which are generally loaded with oxygen, carbon, and hydrogen atoms. All of these light atoms can be better analyzed with neutrons as opposed to x-rays. The reason lies in the very nature of x-rays, which scatter off electrons and do so more powerfully when there are more electrons in the atom.

On the other hand, neutrons scatter off an atom’s nucleus, but instead of simply getting stronger when there are more nucleons––that is, when the atom is heavier––the scattering patterns vary randomly according to the number of nucleons. For example, hydrogen, which has one proton, looks completely different than helium, which has two. “When you consider that a lot of our products contain polymers,” says Nakatani, “x-ray scattering methods become a lot less powerful for us.”

Down the polymer path
Rohm and Haas specializes in making unique materials for its clients, and Nakatani points out that multi-component mixtures such as polymer blends are often the key to creating a new material with particular properties. Different polymers do not, as a rule, play well together because they are hard to mix. If you want a new material with the properties of two different polymers, like styrene and methyl methacrylate, one needs to be able to look at the microstructure of a blend to make sure they do not just phase separate––with each polymer concentrated on different halves of the sample, like separating oil and water.

“Any company that is dealing with multi-component materials has to know how well dispersed the different phases are,” says Nakatani. “The neutron experiments give us that kind of answer.”

Advantageous for all
Not only are neutrons great for looking at light elements, but since they interact with nuclei they can distinguish between isotopes. Indeed, neutron scattering changes dramatically due to isotopes. Neutron beams see hydrogen differently than its more stable cousin deuterium. Hydrogen is made of one proton and one electron, whereas deuterium is an isotope of hydrogen, which means it is almost identical, but with an added neutron. Under x-ray imaging, the x-ray scatters off that single electron the same way for each atom and so is unable to tell them apart. Neutrons on the other hand, since they scatter off the nucleus, can detect that extra neutron. This opens up the door to study the details of a polymer’s structure by labeling specific atoms with deuterium. In a neutron pattern, these labels jump out against the backdrop of hydrogen as dramatically as if you’d painted them black on white canvas.

“This is one of the most exciting parts of neutron science,” says David Lohse, a senior research associate at ExxonMobil, in Irving, Texas. “It’s great for looking at hydrocarbons, because the deuterium provides this great contrast.”

Lohse says that of all the probes available today, he believes the best way to truly see if polymer blends are mixing properly is to label polymers with deuterium and use neutron beams to determine whether the molecules are well overlapped.

“People are excited about it,” he says, adding that ExxonMobil has a long history of neutron research. “NIST is a great facility and we’ve used it a lot, but for the U.S. to keep up with other parts of the world and to really understand the structure of materials, we need to keep upgrading facilities. The SNS is a part of that.”

One of the immediate advantages of the SNSs stronger neutron beams is that no matter what size your sample, it can be substantially smaller––a plus when studying new materials, which are often initially hard to fabricate.

Probing new materials is not the only arena where the chemical industry might use the SNS. Neutrons are sensitive to magnetism in a way that x-rays simply cannot detect, which could be helpful with semiconductor research. Also, x-ray imaging requires that a sample be crystallized into a rigid state. Neutron sources, however, can look at samples even if parts of them are moving. This opens the door to study, for example, the way oil moves through porous rock––something that would be helpful to oil companies.

Costs vs. research
Of course, the question of how industry interacts with government remains an interesting issue. ExxonMobil, for instance, says that much of their neutron research is not proprietary; however, the SNS plans to charge $20,000 a day for any company doing such proprietary research. With four percent of the Rohm and Haas total budget going to basic research, Nakatani says internal methods must be used to conduct the brunt of its proprietary research instead of paying for an expensive government lab. Much of the chemistry industry conducts fundamental research experiments appropriate for publication, of course, whether through collaboration with academia or simply to generate a better understanding of their products, and it is here where the SNS will prove immediately useful. There are many industry scientists who would like to see the U.S. adopt a policy similar to that of European countries, which in an effort to support economic growth will allow industry the same access to government facilities as academics. Regardless, Oak Ridge is ramping up for an influx of users––many of whom they expect will be from the chemical industry––predicting up to five percent of whom will be doing proprietary research.

Karen C. Fox is a freelance science writer based in Washington, D.C. She is the author of Einstein A to Z and The Big Bang Theory: Where it Came From, What It Is, and Why It Matters.

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