Aerial View of the Advanced Photon Source (APS), one of seven synchrotron lightsources in the United States and about 50 worldwide. (Photo: Argonne National Laboratory)
There are 15,000-17,000 particle accelerators in the world. Yes, those numbers are correct! So where are they all?
A summary table in a document from the International Linear Collider collaboration discussing technology benefits of accelerators (PDF) includes the following counts of accelerators for various uses:
>7500 radiotherapy
>7000 ion implanters, surface modification
>1500 industrial processing and research
~1000 research including biomedical research
~200 medical radioisotope production
~120 high-energy accelerators (>1 GeV)
~50 synchrotron radiation sources
In a presentation at the American Physical Society meeting in Denver, Colorado, Murray Gibson from Argonne National Laboratory gave a quick overview of the broad range of applications for just a small subset of these accelerators: the synchrotron radiation sources and neutron sources.
He concentrated on showing the interplay between X-rays, electrons, and neutrons as probes of the very small, showing how they each allow complementary views of atoms, molecules, and materials. They each offer different levels of penetration into materials and views on different size and time scales.
Gibson gave a whirlwind tour of applications of the X-ray synchrotron source at Argonne National Laboratory, the Advanced Photon Source. Similar applications are explored at synchrotrons at SLAC National Accelerator Laboratory, Brookhaven National Laboratory, and Lawrence Berkeley National Laboratory, and three others in the United States and dozens of other synchrotrons around the world.
Some of the synchrotron lightsource examples Gibson mentioned are:
Energy applications
- Better burning: ANL is trying to watch in real time the combustion of fuel to improve the efficiency of engines.
- Artificial solar cells: by understanding how photosynthesis and other natural processes work, new materials that convert solar energy into electrical energy might be developed.
Climate research
- Carbon capture: by understanding how sea animals capture carbon, sequestration techniques might be better developed.
- Free radicals: understanding atmospheric chemistry will help remove damaging free-radicals from the atmosphere.
Biology
- Drug development: companies use synchrotron beamlines to develop better structures for new medications.
- Protein structures: more than 1000 protein structures are solved each year just at the Advanced Photon Source.
- Diseases: structural and dynamical information contributes to understanding the mechanisms of diseases and conditions ranging across viruses that attack cancer, autism, dental conditions, and obesity.
Infrastructure
- Metal fatigue: understanding how metals fatigue on a molecular level would allow engineers to prevent events such as bridge collapses.
- Oxide scales: knowing more about the structure of oxides in metals could save the US hydrogen industry vast amounts of money each year.
This list just touches on a few areas explored at these facilities, but shows the range of applications for accelerator-driven X-ray lightsources.
Neutron sources are complementary to X-ray sources in many cases. They typically start with a proton accelerator which bombards a target that then emits neutrons. (The process is called neutron spallation.) That beam of neutrons is used as the probe for looking into larger thicknesses of material, and is particularly good for examining magnetic materials, as neutrons are sensitive to magnetic effects where X-rays are not.
Studies with neutrons cover almost as broad a range of topics as X-ray studies. Here are some of them:
- Hydrogen storage and fuel cells, with use of deuterium to identify structures
- Exploring the possibility of welding instead of rivets in airplane construction
- Finding the positions of oxygen atoms in the structure of high-temperature superconductors
- Finding precise positions of hydrogen atoms in protein structures, including some protein dynamics
- Understanding how industrial palladium catalysts are "poisoned" by adsorbates over time
- Understanding high-pressure environments like the Earth's interior
- Developing higher-density digital storage, including spintronics
Imaging structures and dynamics with X-rays, neutrons, and electrons touches on nearly every area of science. The facilities, all driven by accelerators, are allowing scientists to understand matter and materials on a molecular level in a way never before possible.
