The SNS is a story of world leadership lost and regained.
Neutron scattering was born in Oak Ridge at the Graphite Reactor, built under Enrico Fermi in 1943 for the Manhattan Project at the site that became Oak Ridge National Laboratory. The reactor's purpose was to demonstrate the viability of extracting fissionable plutonium, a byproduct of the reactor's operation. The discovery made possible the development of the atomic bomb that ended World War II.
For almost three decades, the United States led the world in neutron science, a leadership based in part on research reactors at Oak Ridge National Laboratory. In the 1970s, the U.S. surrendered the leadership role to Europe, where a new and larger generation of neutron sources was built in France and Great Britain. The story of the Spallation Neutron Source is also the story of how America, through a series of scientific and political twists and turns, set about to regain the status of world leader in neutron scattering and materials research.
As the war came to a close, health physicist Ernest Wollan had a unique interest in the neutrons produced by nuclear fission in the Graphite Reactor. He built a neutron diffractometer and sought to understand whether neutrons from the reactor could serve as a probe of the atomic structure of solids. In 1945 Clifford Shull joined Wollan in conducting neutron diffraction research. Shull conducted pioneering work in elastic neutron scattering at ORNL until 1955 when he left for a position at the Massachusetts Institute of Technology. In 1994 Shull and Bertram Brockhouse of Canada shared the Nobel Prize in physics for pioneering the use of neutron scattering to study material structure and dynamics.
Significant neutron scattering research continued at the Oak Ridge Research Reactor, which went critical in 1958, and the High Flux Isotope Reactor (HFIR), which began operating in 1966. HFIR's experiments yielded considerable information on the magnetic properties of rare earths and other elements.
Europe Takes the Lead
In the early 1970s, the High Flux Reactor at the Institut Laue-Langevin in Grenoble, France, began operations. Compared with HFIR in Oak Ridge, the ILL reactor offered higher neutron intensities as a result of improvements in instrumentation, neutron beam optics, and source tailoring, as well as a more open user program. ILL attracted neutron scattering researchers throughout the world seeking to study material structure and dynamics. About a decade later in 1984, the British opened the world's leading pulsed neutron source near Oxford. With these two facilities, Europe had wrested away the leadership in neutron science.
In the search for high-flux neutron sources to produce nuclear materials, researchers realized that, because of limitations in the reactor core power density, the use of a high-energy particle to spall neutrons from a heavy nucleus offered a better path to higher fluxes than nuclear fission for producing a neutron beam. In the 1980s, two accelerator-based spallation sources were built—KENS in Japan and Argonne's Intense Pulsed Neutron Source. Research at both facilities pioneered the development of a spallation target, a pulsed proton beam to produce neutrons in pulses, and time-of-flight scattering instruments.
Beginning in the early 1980s, the U.S. scientific community began aggressively advocating for a world-class reactor-based, neutron source closer to home. Many wanted a higher-performance reactor with a cold source, like the French reactor, to slow neutrons down to make possible research on polymers and proteins. The Department of Commerce responded by installing a cold source, guide hall, and neutron diffractometers and spectrometers at the reactor at what is now the National Institute of Standards and Technology Center for Neutron Research in Gaithersburg, Maryland.
Even with improvements in the existing American neutron sources, a major new facility was needed to satisfy increasing U.S. research requirements and to regain world-class status in neutron science. Since the late 1970s every national panel that reviewed the status of U.S. neutron science recognized the disparity between U.S. and European neutron sources and called for a new American facility.
A Twenty-year Effort
In 1984, in response to the President's Office of Science and Technology Policy, the National Research Council appointed the Seitz-Eastman committee to review U.S. needs for materials research facilities. The committee consisted of 22 distinguished researchers, headed by Frederick Seitz, president of Rockefeller University and former ORNL reactor school director, along with IBM vice president Dean Eastman, who later served as director at Argonne National Laboratory. In March 1984 ORNL's Ralph Moon made a presentation on neutron scattering to the Seitz-Eastman committee. The committee's report, Major Facilities for Materials Research and Related Disciplines, recommended an intense, synchrotron-based, X-ray source (which was later built at Argonne and called the Advanced Photon Source), and construction of a new high-flux, steady-state neutron source designed to have a neutron flux 5 to 10 times that of the French reactor. The committee's recommendations also included the development of a plan leading to a high-intensity, pulsed neutron facility.
In 1993 the Department of Energy's Basic Energy Sciences Advisory Committee Panel on Neutron Sources for America's Future reaffirmed the Seitz-Eastman committee's recommendations. The University of California at Santa Barbara's Walter Kohn, who had been a member of the Seitz-Eastman committee, headed the panel. The Kohn Committee concluded that “the nation has a critical need for a complementary pair of sources: a new reactor, the Advanced Neutron Source, which will be the world's leading neutron source, and a pulsed spallation source. The Advanced Neutron Source is the Panel's highest priority for rapid construction. In the Panel's view, any plan that does not include a new, full-performance high-flux reactor is unsatisfactory because of a number of essential functions that can be best or only performed by such a reactor.”
In his 1993 report, A Vision of Change for America, President Clinton urged the U.S. Congress to build the ANS. He included the proposed 330-megawatt ANS, to be constructed in Oak Ridge, in his 1995 budget.
Despite the backing of the scientific community, the ANS could never get off the ground. Against the recent backdrop of the Superconducting Supercollider project in Texas, which was cancelled after the expenditure of more than one billion dollars, proponents of the ANS could not persuade a skeptical Congress to commit another $2.9 billion for a project whose benefits, frankly, many did not understand. Opposition to the ANS was compounded by concerns from the State Department about the facility's potential to complicate nonproliferation efforts. Meanwhile, as the debate dragged on without resolution, accelerator technology was making significant strides.
In 1995 DOE regrouped, recommending cancellation of the ANS reactor project and allocating $500,000 to ORNL for initial scoping studies on a spallation neutron source estimated to be about one-third the cost of the ANS. DOE's Basic Energy Sciences Advisory Committee recommended in 1996 the design of an accelerator-based, spallation neutron source that could begin operation at a beam power of approximately 1 megawatt. To meet the continually growing needs for an intense source, their recommended design would be sufficiently flexible so as to be upgraded to significantly higher power in the future. On August 19, 1996, DOE initiated the Spallation Neutron Source project with the formal “Approval of Mission Need.”
Under the leadership of ORNL's Al Trivelpiece and Bill Appleton, work began on the conceptual design of the SNS by a consortium of six DOE laboratories. The group identified a wooded 75-acre site on Chestnut Ridge, about one mile from the main ORNL campus. After a slow start, a team from Argonne National Laboratory, headed by David Moncton, led the transition to construction. On December 15, 1999, with Vice President Al Gore of Tennessee holding the shovel, the groundbreaking ceremony occurred.
Significantly, the construction phase of the SNS project got under way less than a month after DOE selected UT-Battelle to replace Lockheed Martin as the managing contractor at ORNL. Skeptics expressed concern about “changing horses in the middle of the stream” with a project on which so much was riding for DOE and the scientific community. Questions persisted in 2001 when ORNL Director Bill Madia selected Thom Mason, a 36-year-old Canadian, to take over the SNS project in the same year Congress was being asked to provide an imposing $281 million in construction funds.
Time and events proved the skeptics wrong. The partnership among the six DOE laboratories functioned well. Construction went forward on time and on budget. Annual reviews of the project were positive, which in turn attracted international talent. Gradually, confidence within the Administration, the Congress, and the scientific community grew until one of the world's largest science projects enjoyed an unprecedented degree of political support.
On April 28, 2006, ten trillion protons were fired into the mercury target of the SNS, releasing neutrons in a process that would help define American science for decades to come. The result was both tangible and symbolic. At that precise moment, the men and women who gathered around the SNS control room could look back with pride, knowing they are the heirs to the legacy of Clifford Shull and Enrico Fermi, and that they have restored to Oak Ridge—the birthplace of neutron scattering—the world's leadership in neutron sciences.
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