Cornell High Energy Synchrotron Source (CHESS)
The x-rays produced by particle accelerators at CHESS power new types of microscopes that can image the chemical and atomic composition of a specimen without damaging it. With x-ray fluorescence (XRF) microscopy, high-energy x-rays hit an object, causing the atoms in the material to create “fluorescence” and give off light. The colors of this light are unique to the particular atom being struck. Because of this, XRF has proven itself a versatile tool to “fingerprint” various types of materials. Beyond standard usage of XRF for physical and chemical sciences, CHESS hosts easy-to-use XRF microscopes for art historians, archaeologists, environmental scientists, dendrochronologists, and many others.
This specialized equipment allows scientists to hold specimens and translate them through x-ray beams, all while analyzing the XRF light to identify elemental composition. Both the x-ray beams and the XRF light often travel easily through dense materials, so XRF can serve as both a surface and a bulk analysis tool.
Microcrystallography refers to the process of obtaining useful structures from small (< 30 μm) crystals, or from small regions of “normal-sized” crystals that have bad growth habits or that suffer from rapid radiation damage. Life scientists studying membrane proteins drive this area of research, as protein specimens are hard to obtain, so it is useful to be able to collect data from ultra-small volumes. Understanding the structure of a given protein provides useful information to various diseases and functions, such as HIV infection, causes of cancer, photosynthesis, and more. The Macromolecular Diffraction Facility at CHESS (MacCHESS) has three high-powered x-ray stations dedicated to protein crystallography and structural biology.
Biological small-angle x-ray scattering (BioSAXS) is an experiment similar in setup to x-ray crystallography, except that no Bragg spots—the diffraction pattern generated from x-rays passing through a crystal—are generated. What appears is a smooth featureless gradation of intensity very close to the beamstop. As biologists investigate complex systems and proteins that prove challenging to crystallize, BioSAXS offers the ability to provide valuable structural information using a solution-based technique. The technique is applicable to a wide range of solution conditions (concentration, pH, ionic strength, temperature, and additives) and has become an important tool for gleaning structural information early in the research process, for diagnosing problems, and for understanding structure and association under physiological conditions. BioSAXS also makes it possible to study biological systems more in the context of biologically relevant multi-macromolecule complexes. The home for BioSAXS is CHESS’s G1 line. The G-line chem room has a dedicated BioSAXS sample preparation area, as well as high-quality ultrapure water on tap and all the equipment researchers need to prepare a wide variety of buffers.
Science taking place at the G3 line focuses on surface-sensitive x-ray scattering at time scales relevant to thin-film growth. The G-line, fed by positron beams, has optics with an internally water-cooled collimating mirror, two pairs of synthetic multilayer monochromators, and two additional monochromatic mirrors. G3 is the ideal station for flux-limited experiments, as well as feasibility studies involving novel optics and detectors. A key and unique feature of G3 is the presence of in-hutch gas cabinets that allow for the use of hazardous gases often employed for thin-film growth and processing. G3 also houses a 348-nm excimer laser for pulsed laser deposition. Examples of prior studies include the use of specular and diffuse scattering to characterize the interplay of surface time and length scales during pulsed laser deposition.
Researchers use XES to take measurements of the electronic structure of materials to better understand how they function at the atomic level. CHESS scientist Ken Finkelstein and engineers Aaron Lyndaker and Tom Krawczyk developed a unique, high-resolution spectrometer for x-ray fluorescence studies. The spectrometer name, DAVES, stands for Dual Array Valence Emission Spectrometer. It uses an independent control of arrays of spherical analyzer crystals, and detectors for simultaneous collecting spectra from a sample with more than one active emission site. Up to five crystals can collect each emission spectrum.
DAVES also features two-color collection capability, which was included because nature has evolved many proteins utilizing more than one metal active site to effect difficult chemical reactions. The DAVES design enables a doubling in signal collection capability, improved geometry for helium flight paths, enhanced flexibility in designing new experiments, and optimizing data collection methods.
The Integrated Simulation and X-ray Interrogation Tools and training for micromechanics (InSitμ) center helps researchers study the mechanical behavior of structural materials—the materials used to support loads in buildings, bridges, aircrafts, and cars. InSitμ provides enhanced user support for the high-energy x-ray diffraction (HEXD) methods developed at the CHESS A2 and F2 experimental stations over the past decade, as well as the crystal-based finite element code (FEpX) developed by Paul Dawson, Mechanical Engineering. Used together, the data and model can help reveal life-limiting processes, such as plasticity and fatigue crack initiation in structural materials. The goal of the center is to make HEXD and FEpX available to engineers working on today’s important structural problems.
The CHESS capillary optics group makes specialized x-ray optics for microbeams at CHESS and other laboratories. Using the custom-built hardware and software, the capillary optics group designs and creates customized optics from hollow glass tubing. A drawing tower, consisting of a precision linear air bearing and small-bore electric furnace, makes it possible for CHESS staff to soften the wall of the glass tubing and stretch it to the desired shape. The applications of these capillary optics range from protein crystallography for biology to solving problems in art history of paintings. The long-term goal is to make higher quality capillaries with less slope and figure errors to make even smaller diameter microbeams for x-ray experiments.
CHESS invests considerable resources toward the education of graduate, undergraduate, and K–12 students. More than 540 PhD degrees have been awarded based on work done at CHESS since its inception. CHESS’s mission is to serve as a synchrotron science incubator by involving students at all levels, from behind the primary shielding wall, to design of the beamlines, to performance of the experiments, to analysis and presentation of the results. It is the most productive training center in the United States for new beamline scientists. The G-line stations in particular continue this mission: graduate students built G-line as part of their thesis research, and it continues to be operated and maintained by graduate students.
CHESS involves undergraduate students in scientific research—as members of faculty research groups who visit CHESS to do experiments, as part of the Research Experience for Undergraduates program sponsored by the National Science Foundation, and through casual summer or term-time employment.
Xraise is a program dedicated to working with preKindergarten –12 educators from the local Ithaca City School District and beyond to develop student science learning opportunities. The programs range from taking first graders to the eXploration station to discover how materials expand when heated and contract when cooled to working with the sixth graders with investigations and discussion about electricity and magnetism.
The Cornell High Energy Synchrotron Source (CHESS) is a user-oriented National Facility that provides state-of-the-art synchrotron radiation (SR) facilities to the Cornell and broader scientific community. SR, a key research tool, enables major discoveries across diverse fields. Researchers who use CHESS study the atomic and molecular structure and time-resolved behavior of materials in biology, chemistry, polymer science, environmental science, physics, art, archaeology, and electronic and structural engineering. Each year, 400–500 scientists and scientists-in-training from academia, industry, and government visit CHESS to collect data for research.
CHESS, constructed as a synchrotron x-ray facility to the Cornell Electron Storage Ring (CESR) High Energy Physics program, operates with six beamlines—A, B, C, D, F, and G—providing 11 experimental stations. CHESS also has a biohazard level BL3 facility. Other features include a modern darkroom, a cold room for crystal mounting, experimental laboratories for user setup, a central computer facility, and a machine shop. A user lounge is also available to help make a long 24-hour day more comfortable.