EMU, the high resolution backscattering spectrometer at ANSTO
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Date
2016-11-29
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Australian Institute of Nuclear Science and Engineering
Abstract
The energy range and resolution of backscattering spectrometers are well suited to characterizing relaxations on an atomic and molecular scale, such as diffusion processes occurring in e.g. polymer chains, membranes, proteins, molecular crystals, between interstitial crystal lattice sites. The EMU spectrometer can be used to study the dynamics of water molecules in the confined space of a host structure or ionic diffusion in conductor materials. In addition, quantum rotational tunnelling of functional groups (e.g. -CH3, -NH4) and hyperfine splitting of nuclear energy levels can be investigated. Relaxation times from a few 10 ps to over 1 ns are accessible. We will present the first -CH3 tunneling and diffusional motion spectra, obtained during the instrument commission, as an example of EMU’s present capabilities. The experiments have been performed in a temperature range from 3 – 650K, using top- and bottom-loading cryo furnaces. Other sample environments such as pressure, magnetic fields, controlled gas delivery systems, sub-K cryostats etc. are also available or currently under testing. EMU entered user service in 2016 and we welcome proposals in a wide range of scientific disciplines. The EMU instrument has the highest energy resolution of the neutron spectrometers at ANSTO and provides a momentum transfer range from as low as 0.1 Å-1 up to 1.95 Å-1. The high energy resolution is obtained by neutron backscattering, which occurs twice, through spherical focusing onto the sample, located between the Si (111) crystal monochromator and the analyser arrays [1]. A linear Doppler drive modulates the incident neutron energies over an energy range of ± 31 µeV. The inelastic scattered neutrons are counted in two 3He linear-position sensitive detector arrays.
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Keywords
Backscattering, Diffusion, Spectrometers, Measuring instruments, Monochromators, Radiation detectors
Citation
de Souza, N. R., Klapproth, A., & Iles, G. N. (2016). EMU, the high resolution backscattering spectrometer at ANSTO. Paper presented at 13th AINSE-ANBUG Neutron Scattering Symposium, Sydney, NSW, Australia, 29-30 November 2016.