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PHASE-CONTRAST IMAGING WITH NEUTRONS
FILTER-ANALYZER NEUTRON SPECTROMETER (FANS).
THE NCNR DISK CHOPPER TIME-OF-FLIGHT SPECTROMETER (DCS).
ULTRA-HIGH RESOLUTION SMALL-ANGLE NEUTRON SCATTERING (USANS).
LIGAND DYNAMICS IN Mn[N(CN),2.PYRAZINE .
PROBING DISORDER IN CONFINED METHYL IODIDE
PRESSURE-INDUCED INTERLINKING OF CARBON NANOTUBES: COMPUTATIONS
DYNAMICS CHANGES IN THE MOLTEN GLOBULE-NATIVE FOLDING STEP
SOFT PHONON ANOMALIES IN RELAXOR FERROELECTRICS
LITHOSILICATES: A NEW FAMILY OF MICROPOROUS MATERIALS
QUANTIFICATION OF PHASE FRACTION AND AMORPHOUS CONTENT
DIFFRACTION ELASTIC CONSTANTS FOR ARBITRARY SPECIMEN AND CRYSTAL SYMMETRIES
DIRECT OBSERVATION OF SUPERHEATING AND SUPERCOOLING OF VORTEX MATTER
SANS MEASUREMENTS OF NANOSCALE LITHOGRAPHIC FEATURES
ASYMMETRIC MAGNETIZATION REVERSAL IN EXCHANGE-BIASED HETEROSTRUCTURES
THE ROLE OF THE CRP/CAMP PROTEIN COMPLEX IN DNA TRANSCRIPTION
POLYMER THIN FILMS UNDER SUPERCRITICAL CO2
COLD NEUTRON DEPTH PROFILING OF LITHIUM BATTERY MATERIALS
SERVING THE SCIENTIFIC AND TECHNOLOGICAL COMMUNITIES
THE CENTER FOR HIGH RESOLUTION NEUTRON SCATTERING
REACTOR OPERATION AND ENGINEERING
CHEMICAL PHYSICS OF MATERIALS.
Inside Back Cover
proposal was made to the National Science Foundation (NSF) to allow joint NIST/NSF operation of the three high-resolution instruments, and to construct a new cold neutron triple axis spectrometer. The final disposition of this application is not yet available, but the external reviews are complete, a site visit has taken place, and the NSF is now considering the appropriate action. If this proposal is funded, then we will be able to operate these new inelastic scattering instruments properly in a full user mode.
Finally, as always, the results are seen in the output of the researchers who use the facility. As has become our practice, we are presenting highlights of this work in the following chapters of this report. I think that all can agree that the results truly speak for
nce again, it is a pleasure to be able to reflect on the accom
plishments of the NIST Center for Neutron Research over the past year. The reactor shim control arms were replaced during a planned shutdown early in 2000. As a result, the reactor was scheduled to operate for 212 days during the reporting period, and did operate 198 days, or 93 % of the scheduled time, as a consequence of one unplanned maintenance shutdown. Construction was begun on the new cooling tower which will not only provide needed capability for the next 25 years, but will also reduce the plume visibility during cold weather. The cold source availability for the period was 98 %; i.e., the cold source held the reactor from operation 4 days during the year. The second-generation liquid hydrogen cold source passed all required pressure tests, and the final assembly is now being prepared for insertion into the reactor in 2001. Finally, steady progress has been made in preparing for a license renewal application to the Nuclear Regulatory Commission, in order to extend the period of operation beyond 2004.
Three high-resolution inelastic scattering instruments, the High Flux Backscattering Spectrometer, the Disk Chopper time-offlight Spectrometer, and the Neutron Spin Echo spectrometer (highlighted in the 1999 report), are now being offered to users who can tolerate the quirks inherent in getting a new instrument on-line. USANS, the perfect crystal small angle scattering spectrometer (part of the NSF/NIST CHRNS), is installed at the reactor and available for proposals; the first phase of the high intensity Filter Analyzer Neutron Spectrometer is operating with high intensity and good backgrounds; and the design and manufacture of new thermal neutron spectrometers is underway. (USANS, DCS, and FANS are highlighted in this report.) This simultaneous development program has put severe strains on our resources, but we can now look forward to many years of benefit from the results. During the past year, a
odern technological society is dependent upon increasingly details of which are stringent tests of nuclear theory; and the effects
sophisticated use of materials, many of whose attributes are of various external influences such as gravity or magnetic fields on dictated by their sub-microscopic structural and dynamical proper- neutrons. ties. A wide range of scientific techniques, of which the many types The NCNR utilizes neutrons produced by the 20 MW NIST of scattering (for example, X-rays, light, electrons, neutrons) are Research Reactor to provide facilities, including the Nation's only arguably the most important, provide knowledge of these properties. internationally competitive cold neutron facility, for all of the above
these probes, neutrons are perhaps least familiar, but they provide types of measurements to a national user community. There are important advantages for many types of measurements.
approximately 35 stations in the reactor and its associated beams Neutrons, as prepared for use at modern sources, are moving that can provide neutrons for experiments. At the present time 27 at speeds comparable to those of atoms moving at room temperature, of these are in active use, of which 6 provide high neutron flux thus providing the ability to probe dynamical behavior. At the same positions in the reactor for irradiation, and 21 are beam facilities. time, neutrons are well matched to measurements at length scales A schematic layout of the beam facilities and brief descriptions of ranging from the distances between atoms to the size of biological available instrumentation are given below. More complete descripor polymer macromolecules. Neutrons are sensitive to the magnetic tions can be found at http://www.ncnr.nist.gov. properties of atoms and molecules, allowing study of the underlying These facilities are operated both to serve NIST mission needs magnetic properties of materials. They also scatter quite differently and as a national facility, with many different modes of access. Some from normal hydrogen atoms than they do from heavy hydrogen instrumentation was built years ago, and is not suited to general (deuterium), allowing selective study of individual regions of molec- user access; however, time is available for collaborative research. ular systems. Finally, neutrons interact only weakly with materials, NIST has recently built new instrumentation (see the highlights in providing the opportunity to study samples in different environments this report on FANS, DCS, and USANS), and reserves 1/3 of availmore easily (at high pressures, in shear, in reaction vessels, etc.), and able time for mission needs with the balance available to general making them a non-destructive probe. These favorable properties are users. In other cases, instrumentation was built and is operated by offset by the relative weakness of the best neutron sources compared Participating Research Teams (PRT); PRT members have access to x-ray or electron sources, and by the relatively large facilities to 75 % of available time, with the balance available to general required to produce neutrons. As a result, major neutron sources users. In a special case, NIST and the National Science Foundation are operated as national user facilities to which researchers come established the Center for High Resolution Neutron Scattering at the from all over the United States (and abroad) to perform small-scale NCNR, with a 30 m Small Angle Scattering (SANS) instrument, science using the special measurement capabilities provided. a cold neutron triple axis spectrometer, and the thermal neutron
In addition to scattering measurements, neutrons can be used perfect crystal SANS commissioned this year. For these facilities, to probe the atomic composition of materials by means of capture most time is available for general users. While most access is for and resultant radioactive decay. The characteristics of the decay act research, whose results are freely available to the general public, as “fingerprints” for particular atomic nuclei, allowing studies of proprietary research can be performed under full cost recovery. Each environmental samples for pollutants (e.g., heavy metals), character- year, approximately 1600 researchers (persons who participated in ization of Standard Reference Materials, and many other essential experiments at the facility, but did not necessarily come here) from measurements. While the scattering and capture users of neutrons all areas of the country, from industry, academe, and government use are little concerned with understanding the inherent properties of the the facility for measurements not otherwise possible. The research neutron, there are important areas in physics that can be explored covers a broad spectrum of disciplines, including chemistry, physics, by carefully measuring fundamental neutron behavior. Examples biology, materials science, and engineering. include the lifetime of the free neutron, an important quantity in the theory of astrophysics; the beta decay process of the neutron, the
1 A Cold Neutron Depth Profiling 3 BT-8 Residual Stress instrument (not shown) for
Diffractometer optimized for quantitative profiling of sub- depth profiling of residual surface impurities currently at stress in large components. this site will be moved to another position. Shown is
4 BT-9 Triple Axis Crystal
Spectrometer for measurea proposed Triple Axis Cold
ments of excitations and strucNeutron Crystal Spectrometer
ture. with double focusing monochromator and multiple crystal 5 Thermal Column A very wellanalyzer/detectors that can be thermalized beam of neutrons flexibly configured for several used for radiography, tomogenergies simultaneously or for raphy, dosimetry and other
high throughput at one energy. experiments. 2 BT-7 Triple Axis Spectrometer 6 BT-1 Powder Diffractometer
with fixed incident energy for Powder diffractometer with 32
of 0.208 nm , 0.154 nm, and