The ISIS targets are surrounded by a series of neutron scattering and muon instruments. The neutron instruments can be broadly grouped into two categories: diffractometers and spectrometers.
Diffraction
Diffractometers look at structures, that is the spatial distribution of atoms, molecules, or larger scale structures. They measure neutrons that have been scattered elastically from a sample, ie. energy has not been exchanged between the neutron and the sample. This process is known as diffraction.
Diffraction instruments at ISIS can be divided into three groups:
Crystallography instruments measure the detailed atomic structure of well-ordered, crystalline materials. The nature of these materials allows long range order to be probed in general. Large Scale Structure instruments use surface reflection and small angle scattering to examine more extended structures, often in solution or bound to a substrate. The use of hydrogen/ deuterium isotopic substitution is often an essential tool in examining the details of such systems. Disordered Material instruments study less-ordered materials such as liquids and amorphous metal alloys. The shorter range order in such materials is of intrinsic interest in understanding the bulk scale properties.
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Spectroscopy
Spectrometers measure inelastic scattering, ie. the change in energy of a neutron when it scatters in from sample, and relate this to the atomic dynamics of the sample. This process is known as spectroscopy.
Spectroscopy instruments at ISIS can be divided into two groups:
Excitations instruments in which processes such as magnetic excitations or recoil scattering in a material are studied, yielding detailed information about the fundamental electronic interactions. Other measurements can determine the collective vibrations of the atoms in a material, known more formally as lattice dynamics. Molecular Spectroscopy instruments investigate very low energy processes such as vibrational and rotational spectroscopy, diffusional processes and quantum tunnelling.
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µSR
µSR stands for muon spin rotation, relaxation, or resonance, or just muon spin research. The µSR technique is a method for investigating the structure and dynamics of matter on the atomic scale by implanting muons into a sample and observing the effects of the local environment on the muon behaviour. Muons act as sensitive magnetometers, sensing the presence of local magnetic and hyperfine fields, and the resonance and precession signals allow these fields to be measured. Subseqent measurement of the time evolution of the polarisation enables the spatial and temporal variations of the internal fields to be followed. Implanted muons can also mimic the behaviour of hydrogen in materials: a muon has the same charge as a proton and one ninth of its mass, so acts like a light proton isotope.
