JUNE 13, 2018
Neutron scattering grew from the nuclear science of the Manhattan Project during the 1940s at what is now Oak Ridge National Laboratory (ORNL).
Today the Department of Energy (DOE) lab in eastern Tennessee operates two powerful neutron scattering facilities for DOE’s Office of Science—the High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS). For over 70 years, neutron scattering has been an invaluable tool for researchers to investigate the fundamental properties and behaviors of energy and materials at the atomic scale. Neutron scattering at ORNL has also played an important role in helping the U.S. Department of Energy (DOE) fulfill its mission of addressing energy, environmental and nuclear challenges through transformative science.
Applying the powerful technique continues to improve materials that enable modern life. For example, it helps scientists develop more effective medicines, more efficient fuels, stronger buildings, lighter vehicles, advanced electronics, and more.
ORNL’s two facilities together offer more than 30 specialized beamlines that attract more than 1,000 researchers each year from government, academia, and industry around the world. Their peer-reviewed proposal process for beam time is highly competitive; many instruments are oversubscribed by nearly 3 to 1.
Like x-rays, neutrons are used to see inside materials at the atomic scale. Because they have a magnetic moment, neutrons are ideal probes for studying magnetic materials used in a wide range of electronic devices such as hard drives and smart phones. They also offer myriad insights into chemical and biological processes because of their sensitivity to light elements such as hydrogen and lithium. For instance, in the past decade, neutrons have played an essential role in advancing the understanding of lithium battery materials.
Neutrons were discovered by English physicist Sir James Chadwick in 1932. A little more than a decade later, two ORNL scientists would be the first to truly harness the particle’s analytical properties and pave the way for a rapidly expanding field that today employs thousands around the world.
Dawn of the Nuclear Age
In 1942, the first self-sustaining nuclear chain reaction was achieved at the University of Chicago, in a reactor described by physicist Enrico Fermi as “a crude pile of black bricks and wooden timbers.”
In attendance was physicist Ernest Wollan, who traveled a year later to ORNL—then known as Clinton Laboratories—to witness the start-up of the X-10 Graphite Reactor.
Wollan soon moved to Oak Ridge to begin work at the one-of-a-kind facility, which was the first nuclear reactor built for continuous operation, 1,000 times more powerful than Fermi’s Chicago Pile-1. During the Manhattan Project, he studied the use of neutrons to measure nuclear materials. That experience, along with his background in x-ray scattering, quickly led him to realize the potential neutrons held as a powerful new method for studying a much wider range of materials.
“That particle called the neutron became my absorbing interest,” Wollan said at the time.
As rumor has it, Wollan left Chicago in the dark of night with an x-ray diffractometer that he would later retrofit to become the world’s first neutron scattering instrument.
In 1944, he wrote a research proposal asking for funding to use the equipment he brought with him from Chicago to measure the diffraction of neutrons using single crystals, identifying an opening in the reactor in which the work could be done.
His proposal was accepted, and shortly thereafter Wollan successfully made the first powder diffraction measurements recorded using neutrons.
The many firsts of Shull and Wollan, neutron pioneers
In 1946, impressed by Wollan’s results, physicist Clifford Shull accepted his colleague’s invitation to work alongside him at the Graphite Reactor to further develop the technique. Shull’s addition had a profound and immediate impact, so much so that he would later be awarded the Nobel Prize in Physics in 1994 for his contributions to the field. In his acceptance speech, Shull expressed his regret that Wollan had not lived to share the award.
Their collaborations quickly led to the construction of the first instrument exclusively for neutron scattering—the double-crystal neutron spectrometer—as well as the adaptation of automated data recording, which took the place of pen and paper and allowed researchers to collect data overnight.
By 1955, the two pioneers had measured scattering patterns from more than 100 elements and 60 different isotopes. A prolific class of successors emerged who would continue to push the field forward and, in turn, mentor what is the present-day neutron scattering workforce.
A short list of Shull and Wollan’s most notable achievements includes
- first neutron Laue photograph ;
- first neutron radiograph;
- first direct evidence of antiferromagnetism and confirmation of the Neel model of ferrimagnetism [2,3];
- first use of neutrons to determine the structure of hydrides ; and
- first measurement of magnetic moment distributions in 3d-electron alloys.