Papers by Adam Washington
RSC Advances
We outline procedures to calculate small-angle scattering (SAS) intensity functions from 2-dimens... more We outline procedures to calculate small-angle scattering (SAS) intensity functions from 2-dimensional electron-microscopy (EM) images for two types of scattering systems.
Underlying data for a paper accepted for publication in The Journal of Physical Chemistry Letters... more Underlying data for a paper accepted for publication in The Journal of Physical Chemistry Letters, American Chemical Society, entitled "Ligand Shell Structure in Lead Sulfide-Oleic Acid Colloidal Quantum Dots Revealed by Small-angle Scattering". http://dx.doi.org/10.1021/acs.jpclett.9b01008.
New with 4.0 The main purpose of this major version release is a significant restructuring of the... more New with 4.0 The main purpose of this major version release is a significant restructuring of the way models work to address one of the biggest issues identified by the community: the difficulty of adding complex custom models. With this release all models are essentially treated the same within the computational framework. The "built-in" models have been separated out into an independent sasmodels package. Custom models continue to be discovered by placing them in the user plugin directory. All models consist of 1 or optionally 2 files: a model.py file containing much of the details (name, parameters, etc) and either the methods for computing intensity or links to an optional model.c which contains the computational code. All models, whether from sasmodels package or in the plugins directory are treated the same by the SasView application. Other things of note in this release: Support for openCL means that running on macs will automatically use GPUs or multiple CPU if the...
Code for the SasView application. Builds can be found here: https://jenkins.esss.dk/sasview/
The dataset contains ASCII files for the following: - Small-angle neutron scattering (SANS) curve... more The dataset contains ASCII files for the following: - Small-angle neutron scattering (SANS) curves and fits for mixtures (mole ratios: 3:1, 1:1 and 1:3) containing polyoxometalate-headed surfactant(P2W17-2Cn, n= 12, 14, 16 and 18) and hydrogenated hexaethylene glycol monododecyl ether (C12EO6) as a function of surfactant total concentrations. Solutions are prepared in two different solvents: deuterium dioxide, 7:3 deuterium dioxide and H2O mixture. - SANS curves and fits for mixtures containing P2W17-2Cn surfactant (n = 12 and 14) and tail-deuterated C12EO6 (mole ratios: 3:1, 1:1 and 1:3) as a function of surfactant total concentrations. Solutions are prepared in deuterium dioxide. The dataset also contains Igor files for the following: - The plot of determination of critical micelle concentrations (CMC) of the mixed P2W17-2Cn/C12EO6 H2O system through surface tension measurements and conductivity measurements.
Alpha release of SasView 4.0 New sasmodels package and redesign of model code to provide polydisp... more Alpha release of SasView 4.0 New sasmodels package and redesign of model code to provide polydispersity in python models OpenCL support for GPU acceleration simpler addition of models for users
Scientific Reports, 2019
To investigate long length scale structures using neutron scattering, real space techniques have ... more To investigate long length scale structures using neutron scattering, real space techniques have shown certain advantages over the conventional methods working in reciprocal space. As one of the real space measurement techniques, spin echo modulated small angle neutron scattering (SEMSANS) has attracted attention, due to its relaxed constraints on sample environment and the possibility to combine SEMSANS and a conventional small angle neutron scattering instrument. In this report, we present the first implementation of SEMSANS at a pulsed neutron source and discuss important corrections to the data due to the sample absorption. These corrections allow measurements made with different neutron wavelengths and SEMSANS configurations to be overlaid and give confidence that the measurements provide an accurate representation of the density correlations in the sample.
Scientific reports, 2015
Eurasian Jay (Garrulus glandarius) feathers display periodic variations in the reflected colour f... more Eurasian Jay (Garrulus glandarius) feathers display periodic variations in the reflected colour from white through light blue, dark blue and black. We find the structures responsible for the colour are continuous in their size and spatially controlled by the degree of spinodal phase separation in the corresponding region of the feather barb. Blue structures have a well-defined broadband ultra-violet (UV) to blue wavelength distribution; the corresponding nanostructure has characteristic spinodal morphology with a lengthscale of order 150 nm. White regions have a larger 200 nm nanostructure, consistent with a spinodal process that has coarsened further, yielding broader wavelength white reflectance. Our analysis shows that nanostructure in single bird feather barbs can be varied continuously by controlling the time the keratin network is allowed to phase separate before mobility in the system is arrested. Dynamic scaling analysis of the single barb scattering data implies that the ph...
In the first decade of the 19th century, an English chemist, William Wollaston, invented an arran... more In the first decade of the 19th century, an English chemist, William Wollaston, invented an arrangement of birefringent prisms that splits a beam of light into two spatially separated beams with orthogonal polarizations. We have constructed similar devices for neutrons using triangular cross-section solenoids and employed them for Spin Echo Scattering Angle Measurement (SESAME). A key difference between birefringent neutron prisms and their optical analogues is that it is hard to embed the former in a medium which has absolutely no birefringence because this implies the removal of all magnetic fields. We have overcome this problem by using the symmetry properties of the Wollaston neutron prisms and of the overall spin echo arrangement. These symmetries cause a cancellation of Larmor phase aberrations and provide robust coding of neutron scattering angles with simple equipment.
It is well-known that the Meissner effect in superconducting materials can be used to provide a w... more It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined nonadiabatic magnetic field transition that can be utilised to produce an efficient white beam neutron spin flipper. Typically these devices utilise niobium and hence require continuous use of liquid helium in order to maintain the device temperature. The use of high Tc materials removes the need for cryogens and has been explored previously and shown to provide efficient flipping of the neutron spin. Improvements in thin high T c films over the past few years make these materials even more attractive.
Physica B: Condensed Matter, 2011
The advantages of neutrons for probing bulk structures are well known: they provide statistically... more The advantages of neutrons for probing bulk structures are well known: they provide statistically averaged correlation functions over a large range of length scales and they are sensitive to light atoms such as hydrogen. These same qualities are, in principle, useful in the study of surfaces and buried morphologies in thin films, especially when the films are polymeric or biological. However, because of the limited sample volume for such systems, the scattering is weak, especially if the neutron beam has to be severely collimated in order to resolve distances of interest (typically 10 to several 100 nm parallel to the surface of the sample). SERGIS is a technique that can potentially overcome these limitations by allowing high resolution measurements of lateral surface structure without requiring tight beam collimation. In this paper we discuss recent progress towards implementing SERGIS both at the Low Energy Neutron Source at Indiana University and on the Asterix reflectometer at the Los Alamos Neutron Science Center (LANSCE). The architecture we use exploits a robust symmetry-related cancellation of Larmor phase aberrations. The spatial resolution it achieves closely mimics that of the ideal magnetic Wollaston prisms. To make progress in understanding SERGIS, we have applied it to the measurement of simple diffraction gratings and developed a dynamical theory that accounts quantitatively and without adjustable parameters for all of the data sets we have measured to date. We argue here that, if SERGIS is to be applied to the study of weakly scattering thin films, it will be necessary to develop the technique of dark-field spin echo scattering angle measurement.
Journal of Physics: Conference Series, 2010
We have used SERGIS to probe the surface structure of a silicon diffraction grating of period 140... more We have used SERGIS to probe the surface structure of a silicon diffraction grating of period 140 nm. Experiments were performed at: the Los Alamos Neutron Science Center (LANSCE) pulsed neutron source and the National Institute of Standards and Technology (NIST) continuous wave (CW) reactor neutron source. Although both sets of data show peaks of the spin echo polarization at integer multiples of the grating period, as expected, the results differ in detail. We have developed a dynamical theory, based on a Bloch wave expansion, to describe neutron diffraction from a grating. The theory explains the differences between the two sets of data without any adjustable parameters.
Journal of Applied Crystallography, 2010
Author(s) of this paper may load this reprint on their own web site or institutional repository p... more Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.
The Review of scientific instruments, 2008
Spin echo scattering angle measurement (SESAME) is a sensitive interference technique for measuri... more Spin echo scattering angle measurement (SESAME) is a sensitive interference technique for measuring neutron diffraction. The method uses waveplates or birefringent prisms to produce a phase separation (the Larmor phase) between the "up" and "down" spin components of a neutron wavefunction that is initially prepared in a state that is a linear combination of in-phase up and down components. For neutrons, uniformly birefringent optical elements can be constructed from closed solenoids with appropriately shaped cross sections. Such elements are inconvenient in practice, however, both because of the precision they demand in the control of magnetic fields outside the elements and because of the amount of material required in the neutron beam. In this paper, we explore a different option in which triangular-cross-section solenoids used to create magnetic fields for SESAME have gaps in one face, allowing the lines of magnetic flux to "leak out" of the solenoid...
Uploads
Papers by Adam Washington