The Disk Chopper Spectrometer at NIST: a new instrument for quasielastic neutron scattering studies

Copley, J. R. D.; Cook, J.C.

doi:10.1016/s0301-0104(03)00124-1

Cited by 268 publications

(225 citation statements)

References 17 publications

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“…Both sets of measurements performed at Chalk River employed a cooled beryllium filter for suppression of higher harmonic incident neutrons. Time-of-flight neutron scattering measurements were performed using the NG4 Disk Chopper Spectrometer (DCS) 40 at the National Institute of Standards and Technology (NIST) Center for Neutron Research. All DCS measurements presented here were performed using an incident neutron wavelenth of 5Å, and a corresponding energy resolution of ∼ 0.09 meV.…”

Section: Methodsmentioning

confidence: 99%

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

et al. 2013

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We present neutron scattering measurements on single crystals of lightly doped La2−xBaxCuO4, with 0 ≤ x ≤ 0.035. These reveal the evolution of the magnetism in this prototypical doped Mott insulator from a three dimensional (3D) commensurate (C) antiferromagnetic ground state, which orders at a relatively high TN , to a two dimensional (2D) incommensurate (IC) ground state with finite ranged static correlations, which appear below a relatively low effective TN . At low temperatures, the 2D IC magnetism co-exists with the 3D C magnetism for doping concentrations as low as ∼ 0.0125. We find no signal of a 3D C magnetic ground state by x ∼ 0.025, consistent with the upper limit of x ∼ 0.02 observed in the sister family of doped Mott insulators, La2−xSrxCuO4. The 2D IC ground states observed for 0.0125 ≤ x ≤ 0.035 are diagonal, and are rotated by 45 degrees within the orthorhombic basal plane compared with those previously reported for samples with superconducting ground states: La2−xBaxCuO4, with 0.05 ≤ x ≤ 0.095. We construct a phase diagram based solely on magnetic order parameter measurements, which displays much of the complexity of standard high temperature superconductivity phase diagrams discussed in the literature. Analysis of high energy-resolution inelastic neutron scattering at moderately low temperatures shows a progressive depletion of the very low energy dynamic magnetic susceptibility as x increases from 0.0125 to 0.035. This low energy, dynamic susceptibility falls off with increasing temperature on a scale much higher than the effective 2D IC TN appropriate to these materials. Appreciable dynamic 2D IC magnetic fluctuations inhabit much of the "pseudogap" regime of the phase diagram.

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Section: Methodsmentioning

confidence: 99%

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

et al. 2013

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“…We obtained dynamic data using the disk chopper time-of-flight spectrometer [DCS] 32 at the NIST Center for Neutron Research in Gaithersburg, MD. The spectrometer was operated at an incident wavelength of 4.2 Å and at a resolution of 0.08 meV (full width at half-maximum).…”

Section: Methodsmentioning

confidence: 99%

Dynamics of PEO in Blends with PMMA: Study of the Effects of Blend Composition via Quasi-Elastic Neutron Scattering

et al. 2008

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We address the dynamic behavior of poly(ethylene oxide) [PEO] in miscible blends with poly(methyl methacrylate) [PMMA] by using quasi-elastic neutron scattering [QENS] with isotopic labeling. The data reveal two dynamic processes in the picosecond-nanosecond time scales: a slow process that is consistent with previous measurements of the segmental relaxation and a composition independent fast process occurring on the picosecond time scale. The composition dependence of the slow process differs from previous measurements, particularly at low PEO content. The fast process is similar to the fast process observed in pure polymers and is insensitive to blending with PMMA. Relaxation times extracted from Kolraush-Williams-Watts [KWW] fits to the data are used to test the applicability of the chain connectivity and coupling models as a function of spatial scale. Both models describe slow process relaxation times within a small range of spatial scales near the Kuhn length of PEO. The effective concentration, when obtained as a fit parameter in chain connectivity model fits, is not a constant, but it decreases with increasing spatial scale.

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“…The quasielastic neutron scattering experiments were carried out on the disk chopper spectrometer [13][14][15] ͑DCS͒ and on the high flux backscattering spectrometer 16,17 ͑HFBS͒ at the National Institute of Standards and Technology Center for Neutron Research. The design and principle of operation of the two instruments are different, and this results in their very different energy resolution and dynamic range.…”

Section: Methodsmentioning

confidence: 99%

Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

Enevoldsen

Hansen

Diama

et al. 2007

The Journal of Chemical Physics

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The dynamics of monolayer films of the n-alkane tetracosane ͑n-C 24 H 52 ͒ and the branched alkane squalane ͑C 30 H 62 ͒ adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics ͑MD͒ simulations. Both molecules have 24 carbon atoms along their carbon backbone, and squalane has an additional six methyl side groups symmetrically placed along its length. The authors' principal objective has been to determine the influence of the side groups on the dynamics of the squalane monolayer and thereby assess its potential as a nanoscale lubricant. To investigate the dynamics of these monolayers they used both the disk chopper spectrometer ͑DCS͒ and the high flux backscattering spectrometer ͑HFBS͒ at the National Institute of Standards and Technology. These instruments made it possible to study dynamical processes such as molecular diffusive motions and vibrations on very different time scales: 1 -40 ps ͑DCS͒ and 0.1-4 ns ͑HFBS͒. The MD simulations were done on corresponding time scales and were used to interpret the neutron spectra. The authors found that the dynamics of the two monolayers are qualitatively similar on the respective time scales and that there are only small quantitative differences that can be understood in terms of the different masses and moments of inertia of the two molecules. In the course of this study, the authors developed a procedure to separate out the low-frequency vibrational modes in the spectra, thereby facilitating an analysis of the quasielastic scattering. They conclude that there are no major differences in the monolayer dynamics caused by intramolecular branching. It remains to be seen whether this similarity in monolayer dynamics also holds for the lubricating properties of these molecules in confined geometries.

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The Disk Chopper Spectrometer at NIST: a new instrument for quasielastic neutron scattering studies

Cited by 268 publications

References 17 publications

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

Dynamics of PEO in Blends with PMMA: Study of the Effects of Blend Composition via Quasi-Elastic Neutron Scattering

Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

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