The Harwell backscattering spectrometer

Windsor, C. G.; Bunce, L.J.; Borcherds, P H; Cole, Ian R.; Fitzmaurice, M; Johnson, Donald F.; Sinclair, Roger N.

doi:10.1016/0029-554x(77)90289-0

Cited by 13 publications

(6 citation statements)

References 8 publications

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“…The simplest detector arrangement would occupy a circle around the sample. However, the instrument resolution ÁQ/Q varies approximately as a function of TOF (t), flight path (L) and scattering angle () (Huq et al, 2019;Windsor et al, 1977):…”

Section: The Influence Of Detector Placementmentioning

confidence: 99%

Simulating and benchmarking neutron total scattering instrumentation from inception of events to reduced and fitted data

Metz¹,

Huegle²,

Olds³

et al. 2021

J Appl Cryst

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In the design and realization of modern neutron scattering instrumentation, particularly when designing beamline concepts from the ground up, it is desirable to fully benchmark against realistically simulated data. This is especially true for total scattering beamlines, where the future deliverable data is to be analysed in both reciprocal- and real-space representations, and needs must be carefully balanced to ensure sufficient range, resolution and flux of the instrument. An approach to optimize the design of neutron scattering instrumentation via a workflow including ray-tracing simulations, event-based data reduction, heuristic analysis and fitting against realistically simulated spectra is demonstrated here. The case of the DISCOVER beamline concept at the Spallation Neutron Source is used as an example. The results of the calculations are benchmarked through simulation of existing instrumentation and subsequent direct comparison with measured data. On the basis of the validated models, the ability to explore design characteristics for future beamline concepts or future instrument improvements is demonstrated through the examples of detector tube size and detector layout.

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Section: The Influence Of Detector Placementmentioning

confidence: 99%

Simulating and benchmarking neutron total scattering instrumentation from inception of events to reduced and fitted data

Metz¹,

Huegle²,

Olds³

et al. 2021

J Appl Cryst

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“…A full description of the Harwell back-scattering spectrometer (BSS) used in this work is given elsewhere (Windsor et al, 1977).…”

Section: The Time-of-flight Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Analogous experiments with a polychromatic X-ray beam, such as that from a synchrotron radiation source, can be performed with an energy-sensitive X-ray detector (Buras, Staun Olsen & Gerward, 1976). Its high epithermal flux compared with a reactor (Windsor, 1977) allows diffraction at good resolution * Present address: Engineering Department, Plessey Radar, Weybridge, Surrey, England.0567-7394/80/040697-08501.00 to be performed over a wide range of scattering vectors. However, if these sources are to be successfully used for accurate structural studies it is important for TDS corrections to be obtained for time-of-flight experiments.…”

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confidence: 99%

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The thermal diffuse correction in neutron time-of-flight diffraction

Cole¹,

Windsor²

1980

Acta Cryst Sect A

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A numerical method is developed for calculating the thermal diffuse scattering (TDS) correction from phonon inelastic scattering in a neutron diffraction pattern measured by the time-of-flight method. The correction is evaluated for a nickel powder spectrum at room temperature. It is shown to be more important than had been suggested previously. It gives rise to a reduction of the apparent Debye-Waller factor by about 10%. It may also lead to the appearance of the higher-order Debye-Waller factor previously ascribed to anharmonicity. IntroductionIn a diffraction experiment, the measured peak intensity of a Bragg reflection will in general include a contribution arising from the inelastic scattering of the incident beam by phonon excitations; this is referred to as the thermal diffuse scattering (TDS). Several theories have been developed to correct data from monochromatic X-ray or neutron diffraction experiments for the effects of TDS (e.g. Walker & Chipman, 1972;Cooper, 1971;Suortti, 1967). Recently, much attention has been given to the advantages of pulsed neutron sources for diffraction (Carpenter, 1977). In this type of diffraction experiment, scattering from neutrons with different wavelengths present in the neutron pulse can be analysed by timing over a flight path of a few metres to give the diffraction pattern at one or more fixed angles as a function of wavelength. Analogous experiments with a polychromatic X-ray beam, such as that from a synchrotron radiation source, can be performed with an energy-sensitive X-ray detector (Buras, Staun Olsen & Gerward, 1976). Its high epithermal flux compared with a reactor (Windsor, 1977) allows diffraction at good resolution * Present address: Engineering Department, Plessey Radar, Weybridge, Surrey, England.0567-7394/80/040697-08501.00 to be performed over a wide range of scattering vectors. However, if these sources are to be successfully used for accurate structural studies it is important for TDS corrections to be obtained for time-of-flight experiments. Windsor & Sinclair (1976) obtained the neutron diffraction spectrum of powdered nickel by the timeof-flight method and argued that, at the high scattering vectors used, thermal diffuse scattering would appear as a relatively smooth background beneath the Bragg peaks and would have only a small effect on the integrated intensities. This is because the multi-phonon scattering, which grows with increasing scattering vectors, is relatively featureless on a time-of-flight scale. In addition, the increasing overlap of the Bragg peaks implies overlap of the TDS around each peak. However, the values obtained for the Debye-Waller exponent B [defined in equation (22)] were smaller than in previous measurements and this was explained in terms of anharmonicity in the lattice potential.It is well known (Willis, 1969) that the effect of TDS in a conventional constant-wavelength experiment is to produce an apparent reduction in the value of B if no corrections are applied, and similar effects in a time-of-flight expe...

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“…The relationships given in equations (2), (3) and (6) were originally determined empirically (Von Dreele et al, 1982) A fit of the convolution function [equation 1] to a single neutron TOF Bragg peak. peak fits of neutron TOF powder diffraction data obtained from one of the original spallation sources (ZING-P 0 , Argonne National Laboratory; Jorgensen & Rotella, 1982) and an electron linac source (Harwell Linac; Windsor et al, 1977), both equipped with poisoned room-temperature polyethylene moderators.…”

Section: Introductionmentioning

confidence: 99%

On the numerical corrections of time-of-flight neutron powder diffraction data

et al. 2007

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Time-of-flight neutron powder diffraction data for NIST Standard Reference Materials have been used to study the adequacy of the peak profile model obtained from a convolution of back-to-back exponentials with a pseudo-Voigt function that is widely used in Rietveld refinement. It is shown that, while the empirical models for d-spacing (wavelength) dependence of Gaussian and Lorentzian components of the pseudo-Voigt function and rise exponent are satisfactory, the behavior of the decay exponent and peak positions demonstrate significant deviations, which can be corrected by numerical methods. The practical side of this process as implemented in GSAS and FULLPROF and the effect of the corrections on the Rietveld analysis results are discussed.

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The Harwell backscattering spectrometer

Cited by 13 publications

References 8 publications

Simulating and benchmarking neutron total scattering instrumentation from inception of events to reduced and fitted data

Simulating and benchmarking neutron total scattering instrumentation from inception of events to reduced and fitted data

The thermal diffuse correction in neutron time-of-flight diffraction

On the numerical corrections of time-of-flight neutron powder diffraction data

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