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3 Science and Technology at the Center During the past year the NIST Center for Neutron Research has sustained a high level of creativity, productivity, and quality in science and research that primarily take advantage of the neutron-based resources available at the laboratory. Presentations delivered to the Panel on Neutron Research by NCNR scientists and university collaborators covered a wide range of activities, including those in solid-state physics, fundamental neutron physics, polymer science and engineering, biological science, and energy storage. These activities demonstrated a competent staff whose members interact with one another and with a rich complement of outside users. Overall, the work presented illustrates the vital contributions made by the NCNR to the sustenance of fundamental science and the development of technology in the United States and internationally. The following discussion highlights selected recent accomplishments at the NCNR and assesses future opportunities in several areas of investigation. Overall, a high level of technical merit characterizes the neutron science at NIST, and the NCNR addresses a host of national priorities related to basic science and applied technologies. The continuing development of the neutron source, along with the ongoing improvement of existing instrumentation and acquisition of new measurement devices, plays a pivotal role in satisfying the goals of maintaining high technical merit relative to the state of the art and addressing national priorities relevant to NIST. Two calls for proposals during 2008 resulted in the submission of 652 proposals, of which 414 were approved and received beam time. In 2008, 321 proposals resulted in more than 2,200 research participants (68 percent from universities), leading to 320 publications; 11 percent of these appeared in high impact factor journals and 59 percent in journals whose impact factor is greater than 2 (journals of respectable caliber).1 These metrics are comparable to those from the past few years at the NCNR. The fundamental neutron physics program is thriving. A number of experiments are in development or poised to begin, and many will benefit greatly from the higher flux expected after the guide hall expansion. The NCNR should select a few of these experiments and focus its effort on those over the next year in order to demonstrate full viability prior to the shutdown period. One good choice would be the neutron lifetime measurement experiment. The technology for polarizing and analyzing neutron spins by means of transmission through polarized 3He continues to find new applications at the NCNR, particularly in situations where super-mirrors are inapplicable or prohibitively expensive. The group that addresses this technology includes nine scientific staff members, who add a rich and valuable complement to the team of (mostly scattering) scientists working at the NCNR. The neutron activation (NA) metrology program in standards and commerce has good value. The reports of the Analytical Chemistry Division in NISTâs Chemical Science and Technology Laboratory on certification of standard reference materials (13 in 2008) are an 1 Impact factor is a measure of the citations to a journal; it is an indication of a journalâs relative importance in its field. High impact factor journals include Science, Nature, Nature Materials, Proceedings of the National Academy of Sciences, and Physical Review Letters. A journal impact factor, JIF, is calculated by comparing the average number of a journalâs citations over a given time period against the number of articles published in that journal during the time period. 9
additional measure of the productivity of the NCNR, along with journal publications and patents issued. Refurbishment of the thermal column, a stated goal of the management, would allow for even more NA studies to be undertaken. The area of soft and self-assembling materials represents a wide range of topics, including synthetic and natural polymers and surfactant and colloidal dispersions. Various forms of neutron scattering (e.g., SANS, neutron reflection, and spin echo spectroscopy) are pivotal to understanding the statics and dynamics of these systems; accordingly, the NCNR has maintained strength in these subjects for many years. The NCNR continues to play an important in some respects a dominant role in exploring soft materials. Competence within the NCNR staff and an expanded group of outside (mostly university) collaborators have resulted in a group of users whose expertise is state of the art. These activities have been augmented by especially strong collaborations with several universities, notably the University of Delaware, where pioneering in situ rheology/SANS experiments have established connections between the microscopic configuration of surfactants and polymers and the macroscopic stress-strain relationships. Polymers warrant particular attention. With about 100 research scientists, the Polymers Division at NIST is a premier center for the investigation of macromolecular science and engineering, and it is ideally positioned to partner with the NCNR. The division chief has articulated an exciting future for polymers at NIST that includes a closer partnership with the NCNR and draws a bevy of industrial companies to the collaboration. Examples of recent activities include neutron reflectivity from organic semiconductors, organic photovoltaics, and complex fluids. These activities, including the participation by Polymers Division theorists, augur a promising future for soft-materials research at the NCNR. The solid-state physics group produced an outstanding research success during the past year. In response to a request to examine a new compound, La(O,F)FeAs, staff members at the NCNR quickly arranged to obtain powder diffraction patterns, and subsequently inelastic scattering data, during a weekend. It became rapidly apparent that they had determined the essential structural properties of a new type of superconducting material. Within several days the work was submitted for publication, and it soon appeared in Nature. Since this initial publication, many groups have turned their attention to these Fe-based superconductors, which exhibit critical temperatures as high as 55 K and are characterized by nearly isotropic properties, including a superior mechanical response. Significantly, the Fe-based compounds appear to be similar electronically to the cuprate superconductors, offering a tantalizing opportunity to gain valuable insights into the underlying mechanism of superconductivity. These very exciting developments underscore the health of the solid-state program at NIST. While serving the nation through the user facility, NCNR scientists are nimble and capable of acting quickly when opportunities arise. The neutron scattering facilities play a crucial role in this area, and the quality of the instruments and capabilities of the staff are laudable. The solid-state group had another very impressive discovery in 2008. In collaboration with Korea University, the group explored dilute ferromagnetic semiconductor superlattices using polarized neutron reflectometry. Conclusive evidence documented both antiferromagnetic and ferromagnetic order, depending on the temperature and magnetic-field strength. This important discovery provides the first evidence of antiferromagnetic coupling in gallium- manganese-arsenic layers separated by gallium-arsenic-beryllium spacers and promises to guide the future development of new devices. The NCNR should continue to commit to research in biology and medicine. The neutron technologies provided by the NCNR can address certain questions in ways not permitted by other 10
approaches, and such research contributions could become increasingly urgent as biotechnology and medicine grow in their roles in the national economy and the health of the population. While some of the ongoing work is highly relevant and meritorious, the quality is uneven overall, and further insights concerning the questions of interest in contemporary biological science should be sought and developed. Examples of the excellent work include the voltage-gated channel effort, where independent review by the National Institutes of Health (NIH) has resulted in a grant supporting the project to study membrane protein folding in lipid bilayers. Another measure of serious interest is the commitment of effort and materials by outside groups, as in the involvement of scientists at the NIH with the HIV Gag protein project. There are other areas in which a more informed biological overview could lead to more and better use of the instruments. For example, the large community of computational scientists deriving dynamic features of macromolecular function might consider modeling cases in which large conformational changes attend biological functions and making corresponding dynamic measurements, as in the kinase family. Work on membrane bilayers might include studies of the drug interactions that are a key to cellular entry; it should be possible to generally broaden the range of important membrane surface interactions studied with supported bilayers. A large group of scientists is interested in natively unfolded proteins and could benefit from some of the insights that work with neutrons can provide. Some work on these topics is underway at the NCNR, but there should be more, and there must be more effective outreach in order to exploit the opportunities. Examples of communities that might have more involvement include the growing group that is using x-ray solution scattering at the nationâs synchrotron facilities and the community of computational biologists engaged in molecular dynamics modeling. A barrier to substantially increased biomedical research in the areas addressed at the NCNR is the modest level of awareness of neutron science capabilities by those engaged with interesting areas in biology and biophysics. Previous NRC assessment reports have encouraged the NCNR to address this perceived problem by means of direct hires and/or the development of new partnerships, and efforts have been ongoing to accomplish this important aim. Interactions with the nearby groups at the NIH might be improved by finding ways to let the scientists there know which of their scientific questions might be answered by working with the NCNR. Outreach at meetings of professional societies could be better planned and implemented, and a question-based approach might also be effective in that outreach. The Center for Advanced Research in Biotechnology, involving NIST and the University of Maryland, is a step in the right direction. NIST should continue to undertake such steps to realize the full potential of its excellent facilities. 11