Oak Ridge Pays Tribute to its Nobel Prize Winner

Joy, pride, and hope. These were the emotions that Oak Ridge residents and ORNL employees felt October 13, 1994, when it was announced that Cliff Shull had received a Nobel Prize for physics. These emotions were rekindled on April 10 and 11, 1995, when Shull came home from Massachusetts to be honored for his achievements and to describe them in a replay of his Nobel Prize lecture.

The professorial Shull--diminutive in stature but a giant among scientists--had been a resident of Oak Ridge from 1946 to 1955. He and his wife Martha lived on Kentucky Avenue, and his children played with the children of former ORNL Director Alvin Weinberg. He conducted his pioneering research using neutron scattering with Ernie Wollan at the Graphite Reactor of Oak Ridge National Laboratory. He is the first person to receive a Nobel Prize for research conducted in Oak Ridge.

Shull shared the 1994 Nobel Prize in physics with Bertram Brockhouse of McMaster University in Hamilton, Ontario. Shull and Wollan used neutron scattering to determine where atoms are in a crystal, and Brockhouse used this tool to learn how atoms move in a material. Neutron scattering has been used at ORNL reactors and research reactors throughout the world to probe the structure and dynamics of materials. The research has led to development of high-strength plastics and improved magnetic materials used for small motors, credit cards, computer disks, and compact discs.

"This award was greeted with great joy in the neutron science community because of the respect we have for both men and in Oak Ridge because Cliff Shull did the work here that earned him the prize," said Ralph Moon, Shull's first doctoral student at the Massachusetts Institute of Technology (MIT), where Shull spent his career after leaving ORNL in 1955. Moon was master of ceremonies for an April 10, 1995, program at the American Museum of Science and Energy in Oak Ridge, where Shull was honored. Sharing the stage was the original neutron diffractometer that Shull had used for his prize-winning research and that was brought to Oak Ridge from the Smithsonian Institution in Washington, D.C., as a new exhibit for the museum's future ORNL room.

At the ceremony, Oak Ridge Mayor Ed Nephew said the city is proud of Shull's achievements. He presented the scientist with a proclamation declaring April 10, 1995, as "Clifford G. Shull Day" in Oak Ridge.

Shull's Nobel Prize also raised the hope that the Advanced Neutron Source research reactor to be built at ORNL would stay in the president's budget as a construction item and receive congressional funding. That did not happen, but Oak Ridge was named the preferred site for a proposed spallation neutron source, an accelerator to replace the reactor as a future facility for neutron scattering research.

On April 11, before Shull gave his Nobel Prize lecture "Early Development of Neutron Scattering" at ORNL, Tennessee Representative Zach Wamp pledged to Shull that he would support funding for neutron science and would educate fellow congressmen about the need to support activities in neutron science to which Shull had dedicated his life. For neutron scientists, there was still hope for more research opportunities ahead.

The neutron diffractometer now on display in the Oak Ridge museum was built at the University of Chicago using a 1915 design by Arthur Compton, Nobel Prize winner under whom Wollan had done his doctoral research in scattering of X rays from solids and gases at the University of Chicago. "This instrument was designed by a Nobel Prize winner," Moon said, "and it was used by another Nobel Prize winner."

A frequently used photograph of Wollan and Shull with their second instrument was first published in the April 8, 1949, issue of The Oak Ridge National Laboratory News. The photograph is displayed with the original instrument as part of the museum exhibit.

"I last saw this diffractometer in England in 1982 during the celebration of the 50th anniversary of the discovery of the neutron by James Chadwick," Shull said. "Since I last used it, it's been gilded and nicely polished.

"The years I spent in Oak Ridge were really exciting. I left Oak Ridge because of the prospect of teaching at MIT and starting a research program using the new reactor there. Our years at MIT were as wonderful as the earlier period in Oak Ridge."

During his Nobel lecture at ORNL (similar to the one he gave in December 1994 in Stockholm, Sweden, during the Nobel Prize ceremonies), Shull traced the history of the neutron, from its discovery in 1932 to the discovery of fission in 1939 to the demonstration of the first neutron chain reaction in December 1942 in Chicago. He then talked about his collaboration with Wollan that ORNL Director Alvin Trivelpiece called "unusually productive."

"My biggest regret," Shull said, "is that Ernie Wollan did not live long enough to share in the honors that came to people in this field."

Wollan joined the Manhattan Project at the University of Chicago during World War II to work in radiation protection and detection. He developed the first reliable film badge, a pocket radiation dosimeter, and a gamma ray meter that recorded the startup of the Graphite Reactor. Then known as the Clinton Pile, this air-cooled, graphite-moderated reactor was built in 1943 as a pilot plant for the production of plutonium to aid in the design of the plutonium-producing Hanford, Washington, reactors. These reactors produced the nuclear material used in the second atomic bomb dropped on Japan. Wollan came to ORNL in 1944 as associate director of the Physics Division.

In 1945 when the war was over, Wollan and other scientists pondered some possible scientific uses for the Graphite Reactor. Wollan, who had studied X-ray scattering from solids and gases, considered using neutrons from the reactor for scattering studies. In late 1945, he obtained a neutron beam of a single wavelength by passing reactor neutrons through a crystal. He arranged for a neutron spectrometer to be sent to Oak Ridge from Chicago. The spectrometer made possible measurement of the angles at which neutrons are scattered from atoms in a target material and the intensities of the scattered neutrons; such information is useful in determining material structure.

Wollan and Robert Sawyer showed that they could get a "powder pattern" by scattering neutrons in a beam from powder ground from a sodium chloride crystal. They then showed that neutron scattering could do what X-ray scattering could not--detect hydrogen atoms in hydrogen-containing materials. The definitive experiment showed that neutrons scatter differently from water (H2O) than from deuterium oxide (D2O), which contains heavy hydrogen, because of differences in the nuclear properties of the two hydrogen isotopes. Thus, they proved that hydrogen contributes to neutron scattering patterns in a recognizable way.

Shull learned of these results when he first visited Wollan in April 1946 at the Graphite Reactor. A native of Pittsburgh, Pennsylvania, Shull earned a B.S. degree from the Carnegie Institute of Technology and a Ph.D. degree in nuclear physics from New York University (NYU). He was there when O. Halpern and M. H. Johnson of NYU developed the theory of magnetic scattering of neutrons. During World War II, Shull became an expert in X-ray diffraction through his research at Texaco on catalysts being developed for production of high-octane aviation gasoline. Impressed by Wollan's research, Shull came to Oak Ridge to collaborate with him in June 1946, about the time that Sawyer left for Lehigh University.

In his Nobel lecture, Shull said he and Wollan irradiated sodium chloride, calcium chloride, and carbon in diamond dust and graphite powder. They were trying to match intensities of scattered neutrons with material structures. But they failed to find quantifiable relationships; instead, they obtained discrepancies that they called diffuse scattering anomalies.

Eugene Wigner, ORNL research director who received a Nobel Prize in physics in 1963, listened quietly to their problem. Recalls Shull: "Wigner said, `Maybe there's something brand new here.' He urged us to keep trying to quantify the effects. Eugene had more faith in our experiments than we did." They later determined that they had multiple scattering effects that could be sorted out, allowing neutron intensities to be correlated with structure.

In their neutron scattering experiments with sodium hydride and sodium deuteride, Shull said he and Wollan got their "first clear indication of where the hydrogen atoms are." They also obtained scattering patterns showing the locations of hydrogen atoms in ice balls made of water and deuterium oxide. " We used an ice ball machine," Shull said, "but we omitted the flavoring."

By accident, Shull and Wollan were the first to obtain a neutron radiograph, similar to an X-ray radiograph. They had set up an experiment to observe the first neutron Laue diffraction pattern using a single crystal of sodium chloride and a white (all wavelengths) neutron beam from the Graphite Reactor. The diffracted neutrons were detected using an indium sheet, which converts neutrons into photons, followed by a sheet of X-ray film. They had used Scotch tape to piece together strips of indium, and the images of these pieces of tape are clearly visible in the background of the Laue pattern.

Shull said he spent the rest of his career at ORNL using neutron scattering to probe the structure of alloys and magnetic materials. His work in magnetic scattering led to the development of improved magnetic materials that have proved important to the recording and computer industries.

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