Gary W. Lynn

The Bio-SANS instrument at the High Flux Isotope Reactor of Oak Ridge National Laboratory

Small-angle neutron scattering (SANS) is a powerful tool for characterizing complex disordered materials, including biological materials. The Bio-SANS instrument of the High Flux Isotope Reactor of Oak Ridge National Laboratory (ORNL) is a high-flux low-background SANS instrument that is, uniquely among SANS instruments, dedicated to serving the needs of the structural biology and biomaterials communities as an open-access user facility. Here, the technical specifications and performance of the Bio-SANS are presented. Sample environments developed to address the needs of the user program of the instrument are also presented. Further, the isotopic labeling and sample preparation capabilities available in the Bio-Deuteration Laboratory for users of the Bio-SANS and other neutron scattering instruments at ORNL are described. Finally, a brief survey of research performed using the Bio-SANS is presented, which demonstrates the breadth of the research that the instruments user community engages in.

Four-circle single-crystal neutron diffractometer at the High Flux Isotope Reactor

A four-circle neutron diffractometer with a new multi-wafer 331 Si monochromator has been installed and commissioned on a thermal beamline at the High Flux Isotope Reactor at Oak Ridge National Laboratory. The instrument is well suited to studies of nuclear and magnetic structures as a function of composition and temperature, resolving symmetry changes (lattice distortions and local structural changes), mapping the evolution of complex magnetic phases, determining hydrogen bonding, analyzing nuclear and spin densities, mapping diffuse scattering, and exploring fiber diffraction. Three incident wavelengths are available, 1.000, 1.536 and 2.540 A, with intensities of 2.5 × 106, 2.2 × 107 and 8.0 × 106 neutrons cm−2 s−1, respectively. Either high-resolution or high-intensity modes are possible by horizontal bending of the monochromator. With increased bending of the monochromator, the incident flux on the sample passes through a maximum, increasing by ×2.0 for 1.000 A, by ×3.5 for 1.536 A and by ×3.5 for 2.540 A, as compared to the flat condition. The flux increases because the lattice strain in the silicon crystals increases. The ω-scan peak width increases with monochromator curvature and this width versus scattering angle flattens. Given these effects, the monochromator bending can be adjusted to deliver high intensity primarily for crystal structure refinements or high resolution for resolving symmetry changes. In addition to the traditional step-scanning mode, a more efficient continuous-scanning mode was developed, and both these are implemented through a LabView-based control program, i.e. a modified version of the SPICE software package. A 4 K closed-cycle helium refrigerator is permanently mounted on the χ-circle of the goniometer to provide temperature control between 4 and 450 K.

New High-flux Small-angle Neutron Scattering Instrumentation and the Center for Structural and Molecular Biology at Oak Ridge National Laboratory

A number of upgrades are currently being undertaken at the High Flux Isotope Reactor (HFIR), including the installation of a supercritical hydrogen moderator (T ∼ 20 K) that will be one of the brightest cold sources currently available. It will feed four cold neutron guides (CGI-4), each with new instrumentation. CG2 and CG3 are reserved for two new small-angle neutron scattering (SANS) instruments. A 40 m SANS instrument (SANSI), funded by the Department of Energy (DOE) Office of Basic Energy Sciences and the University of Tennessee, Knoxville is designed for CG2. Our 35 m small-angle neutron scattering facility (SANS2 on CG3) is optimized for the study of biological systems as part of a Center for Structural and Molecular Biology (CSMB), funded by the DOE Office of Biological and Environmental Research. In addition to the new SANS facilities, there will be suite of instruments including a reflectometer and a cold triple-axis spectrometer. Both SANS facilities will have variable wavelength and large area (1m2) high count-rate detectors that can translate 45 cm off axis to increase the dynamic Q-range ( 10 15 neutrons/s/cm 2 , the beam intensities (up to 10 7 /s/cm 2 ) will be comparable to the best facilities worldwide and this will enhance our ability to collect data from synthetic and biological macromolecules more quickly and study smaller sample quantities.

The Bio-SANS Small-Angle Neutron Scattering Instrument at Oak Ridge National Laboratory

Oak Ridge National Laboratory (ORNL) has completed the High Flux Isotope Reactor (HFIR) Scientific Facilities Upgrades Project that included installation of a new, high-performance cold source on HB-4 and the construction of a new guide hall at the 85 MW reactor. Two new SANS instruments are served by the cold source: the Bio-SANS instrument, a 35-m SANS instrument dedicated to the study of biological systems (Figure 1), and its sister instrument, the 40-m high-resolution SANS. The performance of these instruments will rival the worlds best. The Center for Structural Molecular Biology (CSMB) has been established at ORNL to support and develop the user research and science programs on the Bio-SANS instrument, as well as the neutron sciences for biology at HFIR and at the Spallation Neutron Source (SNS). See http://www.csmb.ornl.gov for details.

The Center for Structural Molecular Biology (CSMB) at Oak Ridge National Laboratory (ORNL)

The CSMB operates a small-angle neutron scattering instrument dedicated to studying biological samples (BioSANS). The CSMB is also closely allied with the Spallation Neutron Source (SNS). The SANS instrument suite at the High-Flux Isotope Reactor (HFIR) and SNS facilities provide new opportunities for studying biomolecular processes on biologically relevant length and timescales. Bio-Deuteration Laboratory