Spallation Neutron Source
The Spallation Neutron Source (SNS for short) is a national large-scale research facility at Oak Ridge National Laboratory in the US state of Tennessee , at which scientific experiments in materials research , engineering , biology, and nuclear and elementary particle physics are carried out with the help of strongly pulsed neutron beams . About 20 measuring instruments are operated at the SNS.
history
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The SNS was designed and built by a consortium of six US Department of Energy laboratories : the Argonne , Brookhaven , Lawrence Berkeley , Los Alamos , Jefferson, and Oak Ridge National Laboratories. The neutron source was completed in 2006 and the first measuring instruments were available in 2007. The total cost was $ 1.4 billion.
functionality
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The SNS is a spallation neutron source in which protons hit a target made of liquid mercury (Hg) with a pulse frequency of 60 Hz . Initially, negatively charged hydrogen ions (H - ) are emitted from an ion source . In a linear accelerator , the central part of which uses superconducting Nb cavities, the H - ions are then accelerated to 1 GeV. In a diamond membrane, the electron of the H are - ions are removed, so that a pulsed proton beam, which is fed into a storage ring. Proton pulses are extracted from the storage ring and hit the Hg target. The heat generated by the protons in the target is dissipated by a cooling circuit. In the target, a spallation reaction creates fast neutrons that have to be slowed down for the purpose of neutron scattering . This happens either in a water moderator , which delivers thermal neutrons , or in a moderator made of liquid hydrogen at a temperature of 20 K, which produces cold neutrons.
Measuring instruments
The SNS currently operates 20 measuring instruments that enable a wide range of scientific investigations. The measuring time on these instruments is allocated through a competitive selection process. In 2017, 764 external scientists carried out experiments at the SNS.
The measuring instruments at the SNS include several time-of-flight spectrometers for spectroscopy of dynamic processes in solids and fluids (ARCS, SEQUOIA, VISION, CNCS). Another spectrometer (HYSPEC) uses a combination of time-of-flight and three-axis spectroscopy to study lattice vibrations and magnetic excitations in solids. For high-resolution studies of low-energy processes in polymers and macromolecules a standing spin echo spectrometer (NSE) and a backscattering spectrometer (BASE) are available. Two reflectometers (LIQREF and MAGREF) enable experiments at interfaces in liquids and polymers or magnetic layer systems. A powder diffractometer (POWGEN) and a single crystal diffractometer (TOPAZ) are used to determine the lattice structure and magnetic structure of solids. Further diffractometers are geared towards structural investigations of macromolecules (MANDI), measurements of diffuse scattering to investigate disorder in crystalline materials (CORELLI), structural investigations under high pressure (SNAP), the structure of liquids, glasses and nanocrystalline materials (NOMAD) as well as structural investigations in the Engineering (VULCAN). Two small-angle scattering instruments (USANS and EQ-SANS) are available for the investigation of large-scale structures in materials and environmental sciences . In addition, the “Fundamental Neutron Physics Beam Line” (FNPB) enables experiments to investigate the fundamental properties of the neutron. The “Versatile Neutron Imaging Instrument” (VENUS), which is still under construction, will be used to carry out imaging experiments for materials, engineering and environmental sciences.
Individual evidence
- ↑ a b Spallation Neutron Source | Neutron Science at ORNL. Retrieved January 13, 2019 .
- ↑ How SNS Works | Neutron Science at ORNL. Retrieved January 13, 2019 .
- ^ RL Kustom: An Overview of the Spallation Neutron Source Project. Oak Ridge National Laboratory, 2000 [1]
- ^ Neutron Scattering Facilities - Spallation Neutron Source (SNS). Accessed January 13, 2019 .