Thursday 11 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session C - Instruments – Reflectomerters and NSE
P.098 Dynamical theory sets the limits of validity of DWBA on periodic structures
R Ashkar1, R Pynn2 and W Schaich2
1
NIST/ University of Maryland, USA 2Indiana University Bloomington, USA
The development of sophisticated nanofabrication techniques has increased the demand for scattering
measurements to characterize nano- and micro-structures. However, extracting structural information from scattering
data requires an adequate theoretical model. Since complete scattering theories are fairly complicated, many
scattering models use approximations to simplify the calculations. Among these approximate theories is the widely
adopted Distorted-Wave Born Approximation (DWBA), which has been used to describe scattering in many x-ray
and neutron scattering experiments. However, since the DWBA is based on perturbation theory, it can be expected
to break down if it is applied in the wrong circumstances. In the specific case of samples with periodic structures, an
exact dynamical theory is available to describe the scattering. We compare the results of this dynamical theory with
DWBA calculations and show that the approximate theory becomes unreliable when the amplitude of surface
features exceeds a value that depends on the scattering geometry and the scattering potential of the studied
sample.
P.099 Profile retrieval of periodic structures using SERGIS and dynamical theory
R Ashkar1, R Pynn2, A Parnell3, J Plomp4 and R Dalgliesh5
1
NIST/University of Maryland, USA, 2Indiana University Bloomington, USA, 3University of Sheffield, UK, 4Delft
University of Technology, Netherlands, 5ISIS, UK
In principle, off-specular neutron reflection from surfaces or interfaces can be used to obtain information about the
height distribution of the surface providing a suitable theory is available to analyze the scattering data. In the case
of periodically structured surfaces a dynamical theory is needed to account for multiple scattering effects. To
determine how accurately the surface profile can be measured with neutrons, we have carried out Spin-Echo
Resolved Grazing Incidence Scattering (SERGIS) measurements on a set of linear diffraction gratings of well-known
profiles. To interpret the data, a dynamical theory (DT) model, adequate for describing scattering from periodic
structures, is used. The sensitivity of the SERGIS signal to the studied profile and the ability of DT to reproduce this
sensitivity were first tested on gratings with rectangular profiles. Further tests were carried out on gratings with
trapezoidal, sinusoidal and triangular profiles using a thin-sliced DT code. The agreement is excellent in all the cases
where the grating profile is uniform. For gratings with non-uniform profiles the DT model gives a good estimate of the
average profile of the grating weighted by the distribution of the incident neutron beam. This has been corroborated
by supplementary AFM measurements on these gratings, which indicate that the profile at the center of the grating
is in better agreement with the DT prediction than the profile averaged over the whole sample. This is a first step
towards developing a profile retrieval algorithm for periodic nanostructures.
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P.100 Virtual polarized neutron scattering simulations using McStas
E Bergbäck Knudsen1, P Kjær Willendrup1, L Udby2 and K Lefmann2
1
DTU Physics, Denmark, 2NBI, Copenhagen University, Denmark
Polarized neutron scattering techniques (NSE, SESANS, etc.) have become commonplace at neutron sources
around the world. To take full advantage of these techniques, the available simulation tools must also develop
alongside. In latter years the widespread Monte Carlo tools available to the community are gaining fast where they
have unfortunately been lacking in their capabilities for a long time.
A recent development in the neutron simulation software package McStas is to have arbitrary sampled magnetic
fields present in a Monte Carlo simulation. This opens a route to complex magnetic structure simulations of
samples.
We present results from newly performed simulations of polarized neutron scattering in McStas, including NSE and
SESANS.
P.101 Complementarity of neutron reflectometry and ellipsometry measurements to solve complex soft matter
problems on FIGARO and in the PSCM
R Campbell1, K Edler2, S Titmuss3, J Ang4, J White4, J Campos-Terán5, A Piñeiro6, M Costas5 and E Watkins1
1
Institut Laue-Langevin, France, 2University of Bath, UK, 3University of Edinburgh, UK, 4Australian National University,
Australia, 5Universidad Autónoma Metropolitana de México, Mexico, 6Universidad de Santiago de Compostela,
Spain
The neutron reflectometer Fluid Interfaces Grazing Angles ReflectOmeter (FIGARO) came online at the Institut LaueLangevin in 2009, and at around the same time a phase modulated ellipsometer was acquired in the Partnership
for Soft Condensed Matter (PSCM). The two techniques are incredibly complementary for measurements of soft
matter systems at free standing air/liquid interfaces. Neutron reflectometry (NR) using isotopic contrast variation
can be used to measure the scattering excess and determine the structure and composition of interfacial layers
while ellipsometry can be used to measure an equivalent optical excess. At a first look the superiority of NR would
seem clear, yet the smaller illuminated area and faster time resolution means that ellipsometry can also be used to
identify and track inhomogeneities across the liquid surface. Together the insight that can be gained about the
interfacial properties of complex mixed systems, for example those with embedded aggregates or lateral domains, is
often greater than from either technique alone. In this poster we introduce the techniques and present four
scientific highlights from international collaborations involving polymer/surfactant mixtures, polymer/nanoparticle
mixtures, protein/nanoparticle mixtures and cyclodextrin/surfactant mixtures.
P.102 New approaches to fluid interfaces: recent developments on FIGARO
R Campbell and Erik Watkins
Institut Laue Langevin, France
FIGARO is a time-of-flight neutron reflectometer at Institut Laue-Langevin. Equipped with a horizontal sample plane
and optics to deflect the incident beam, the instrument’s design facilitates investigation of structures at fluid
interfaces. Here we present recent developments to extend FIGARO’s capabilities: Grazing incidence small angle
neutron scattering (GISANS) at air/liquid interfaces, neutron reflectivity (NR) at liquid/liquid interfaces, and a novel
method to control area per molecule (APM) of lipids in a solid supported bilayer.
GISANS provides a powerful probe to investigate in-plane nanostructure and ordering at surfaces. Using reflection
geometry, as opposed to transmission employed by SANS, this technique optimizes the signal originating from an
interface. Experiments on FIGARO demonstrate the use of GISANS to study ordering at the air/liquid interface.
ICNS 2013 International Conference on Neutron Scattering
Applying NR to study molecular arrangements at the interface between two liquids (for example, between oil and
water) are currently being developed. FIGARO’s ability to direct neutrons either down or up towards the sample
allows neutrons to be transmitted through either bulk liquid phase and reflected from the interface.
While a Langmuir trough can control APM of molecules at air/liquid interfaces, equivalent control over molecules at
solid/liquid interfaces has proven more challenging. Here we present NR results demonstrating a method for
controlling APM of lipids in a supported bilayer by maintaining them in equilibrium with a monolayer on a Langmuir
trough.
P.103 Refractive analysis of interfaces with neutron beams optimized for a white spectrum (RAINBOWS)
B Cubitt1 and J Stahn2
1
Institut Laue Langevin, France, 2Paul Scherrer Institut, Switzerland
A new technique of refractive encoding for specular reflectometry is described that uses the full white beam without
the need for choppers. Depending on the resolution, gains of many orders in flux are possible opening a new area
of sub-second kinetics in interface research or allowing very small sample areas to be studied. The principle of
refractive encoding simply involves exploiting the dispersive power of refraction to measure the wavelength of
neutrons. The method involves passing a well collimated beam through a block of material with low absorption but
a high scattering length density, Nb, such as crystalline MgF2 or sapphire. The beam, when traversing the interface
from material to air at a low enough angle disperses the beam almost linearly with wavelength with a gradient
of (Nb/pi)1/2. Comparing the gain in available flux one simply has to compare the transmission of the prism
compared to a chopper of the same resolution which can be 100× for high resolution of 2% falling to 10× for
low resolution of 10%. This gain assumes that the collimation is the same for the two cases and it turns out that
the collimation required is the same as required for the first angle in conventional experiments. Therefore this
method is appropriate for a q-range 0.005-0.075 if a wavelength range of 2-30 Å could be exploited. A higher
angle and hence a higher q-range is possible but with diminishing gains over conventional time of flight
measurements. Test experiments have shown the method to work in principle. The analysis of the changes to a
surface structure with a resolution of 50 ms is envisaged.
P.104 Progress on wide angle neutron spin echo spectroscopy at ILL: IN11 and WASP
P Fouquet1, D Bazzoli1, T Bigault1, P Courtois1, O Czakkel1, G Ehlers2, P Falus1, B Farago1, B Giroud1, G Pastrello1, I
Sutton3, E Thaveron1 and F Thomas1
1
Institut Laue Langevin, France, 2Spallation Neutron Source, 3European Spallation Source, Sweden
The high Q / wide angle spin echo spectrometer IN11 has been overhauled and received a new neutron guide and
polarizer in the course of the H14 guide project at ILL. We will look back on an exciting first year of re-commissioning
and user experiments with a strongly improved instrument. The neutron flux of IN11 has increased by a factor of 3
and the coil system was completely re-aligned. Incoherent scattering and magnetic scattering experiments strongly
profit from the improved performance.
In parallel we are now entering the “hot” construction phase of our next generation wide angle spin echo
spectrometer WASP. We will present the project status and discuss selected examples of science that will profit from
the new infrastructure.
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P.105 Optimisation of a planned MIEZE spin echo instrument for magnetic samples at the ESS
R Georgii, W Häußler, G Brandl and P Böni
Technische Universität München, Germany
The MIEZE (Modulation of Intensity with Zero Effort) technique is a variant of neutron resonance spin echo (NRSE),
which has proven to be a unique neutron scattering technique for measuring with high-energy resolution in magnetic
fields. Its limitations in terms of flight path differences will be presented. These have been obtained analytically for
neutron beams with vanishing divergence and with Monte-Carlo simulations for quasi-elastic MIEZE experiments
taking into account beam divergence.
One application of the MIEZE technique could be a dedicated NRSE-MIEZE instrument at the European Spallation
Source (ESS) in Sweden. The optimisation of a particular design based on Montel mirror optics with the help of
Monte Carlo simulations will be discussed here in detail.
P.106 Selene-type reflectometer for extended samples and liquid surfaces
U B Hansen1, T Panzner2, E Rantsiou2, P Korelis2, U Filges2, K Lefmann1, M Cardenas3, J Stahn2 and B Klösgen4
1
Niels Bohr Institute, Denmark, 2Paul Scherrer Institut, Switzerland, 3University of Copenhagen,
Denmark, 4University of Southern Denmark, Denmark
Results from a design study for the European Spallation Source on a neutron reflectometer optimized for extended
or liquid samples will be presented, based on simulations with the neutron ray-tracing package McStas. The
instrument design makes use of the Selene guide concept[1] that applies two subsequent elliptic guides to
transport the neutrons and to illuminate the sample with a broad angle range at one shot. Each elliptic guide
consists of two elliptic mirrors arranged perpendicular to each other and side-by-side. As an advantage the phase
space and the beam spot at the final focal point are almost identical to the situation at the guide entrance. The
beam spot spot size and the divergence can hence be defined far from the sample position such that only the useful
neutron flux is transported through the Selene guide system. This reduces the requirements on shielding, and it
results in low background noise.
The overall instrument length is 30 m long. The design does cover a wavelength range from 4Å to 11Å, resulting in a
resolution from 3.4% to 9.4 %. Fast switching between three different angular settings of 2.5° by use of a mirror in
between the two ellipses provides full coverage of the q-range needed for liquid samples, namely 0.006 Å-1 to 0.78
Å-1.
The most essential scientific case for a horizontal reflectometer is the acquisition of data about interfaces and thin
films at the liquid/gas or liquid/liquid boundary. The instrument is designed to study the structure and, to some
extent, rearrangement dynamics within thin layers by covering a wide momentum transfer range at no more than
three shots.
[1]
J. Stahn, et al. The Eur. Phys. J. Appl. Phys., doi:10.1051/epjap/2012110295
P.107 High-resolution spin-echo-spectrometer: a conceptual design for ESS
S Pasini and M Monkenbusch
JCNS, Forschungszentrum Jülich, Germany
Within the German ESS design update project we are investigating optimized designs for neutron spin-echo
spectrometers. First the very high resolution type was considered. The optimization was separated in two main parts:
beam transport from a (cold) moderator to the (35m distant) sample and magnetic layout of the secondary
spectrometer to enable the best resolution. Beam transport and beam polarization is obtained using a straight, 8
ICNS 2013 International Conference on Neutron Scattering
cm x 8 cm neutron guide with a comparatively short ( 2m) polarizing bender or a polarizing kink. A system of 4 disc
choppers will select the used wavelength frame and suppress frame overlap.
The layout of the proper (secondary) spectrometer follows a combination of design principles, which have been
used in the SNS-NSE spectrometer and a strategy to find a magnetic coil configuration with minimal intrinsic field
integral inhomogeneity. An analogous approach was first applied at ILL to device new IN15 coils. By combining the
active stray field compensation techniques used at the SNS-NSE, which require the use of supercomputing coils,
and coil geometry optimization towards the simultaneous minimum of field-integral inhomogeneity, depolarization
and stray-field a solution was found. The resulting configuration has a 3 times reduced intrinsic inhomogeneity of
field integrals and low stray fields allowing for a working NSE-configuration up to 2 Tm field integral.
P.108 Prospects of polarized neutron reflectometry in PNPI
N Pleshanov
Petersburg Nuclear Physics Institute, Russia
Prospects of polarised neutron reflectometry in PNPI (Gatchina) are discussed. The necessity to set up a park of
neutron reflectometers is invoked by a long-term interest to neutron reflectometry as an efficient technique for
studying nanostructures in physics, chemistry and biology. At the operating reactor WWR-M, it has been suggested
(a) to install the reflectometer REVERANS with the vertical scattering plane; (b) to build the reflectometer TestR to
test (super)mirrors produced in PNPI; (c) to upgrade the reflectometer NR-4M with the horizontal scattering plane for
solving scientific tasks. Further prospects of neutron reflectometry in PNPI are linked to the construction of the
reactor PIK. The reflectometers REVERANS, NeRo (transferred from GKSS), UNISON and NORMA will be installed at
cold neutron beams in the guide hall. The reflectometer UNISON is designed as a working site for developing
polarised neutron reflectometry, each option with its own quick-change platform: (a) the basic platform that
suggests record polarisation both in constant-wavelength and time-of-flight modes to be achieved with
'superpolarising' coatings under development in PNPI; (b) 3D polarisation platforms on the basis of spin turners
(monochromatic beam) and spin selectors (white beam); (c) full neutron reflectometry platforms and (d) spin-echo
encoding reflectometry platforms. The reflectometer NORMA is designed to solve the tasks related to production of
modern neutron optics.
P.109 SESANS with a 3-He polarization analyzer
R Pynn1, 3, H Yan1, K Li1, S R Parnell1, A L Washington1, C Fu4, M Snow1 and T R Gentile2
1
Indiana University, USA, 2National Institute of Standards and Technology, USA, 3Oak Ridge National Laboratory,
USA, 4Shanghai Jiaotong University, China
The polarized-neutron beam line at the Low Energy Neutron Source (LENS) at Indiana University is designed for both
SESANS (Spin Echo Small Angle Neutron Scattering) and SERGIS (Spin Echo Resolved Grazing Incidence
Scattering) measurements. The instrument uses a series of triangular solenoids (magnetic Wollaston prisms) to
encode the scattering angle. We report on recent experiments using a Spin Exchange Optically Pumped (SEOP) 3He
filter as a polarization analyzer on this beam line. This device ensures a uniform analyzing power over the entire
transmitted and scattered neutron beam, eliminating artifacts that have been observed with some polarizingsupermirror analyzer systems. It permits a neutron beam with a relatively large cross section (up to 20 x 20 mm2) to
be used, increasing the signal intensity.
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P.110 Neutron reflectivity at ISIS
S Rogers, R Dalgliesh, C Kinane, J Webster, M Skoda, T Charlton, A Hughes and N J Steinke
ISIS, STFC, UK
Neutron Reflection (NR) is a powerful technique for characterizing thin film systems. Specular reflectivity yields
information on the out-of-plane structure in the range of tens to thousands of Angstroms and off-specular reflection
traditionally provides information on in-plane interfacial structures microns in size. At ISIS there are five NR
instruments. Two of these, Crisp and Surf, are situated on the first target station, TS-1, with the remaining three,
Inter, Polref and Offspec, positioned on the cold neutron optimized TS-2. Crisp and Surf helped to pioneer NR on a
pulsed source with Crisp also demonstrating the power of polarized neutron reflection in the study of magnetic
ordering at surfaces and in thin films. Building on this success, Inter, Polref and Offspec were designed and built on
TS-2. Inter is optimized for the study of liquid surfaces and kinetics. The higher flux and wider simultaneous Q range
available has increased data collection speeds by an order of magnitude when compared to the TS-1 instruments.
Polref is the first purpose built polarized neutron reflectometer at ISIS. The significantly increased flux when
compared to Crisp allows smaller samples (<1cm2) to be studied routinely using polarization analysis. Offspec is
optimized for the study of off-specular reflection using Spin-Echo Resolved Grazing Incidence Scattering. This unique
instrument allows in-plane interfacial structures to be studied on the nanometre lengthscale. Offspec also provides
access to the Spin-Echo Small-Angle Neutron Scattering technique which probes structures that are microns in size.
Current science highlights from the ISIS reflectometry suite will be displayed in this presentation along with
beamline developments.
P.111 Spin echo modulated small angle neutron scattering (SEMSANS) in time of flight mode
M Sales1, J Plomp2, W Bouwman2 and M Strobl3
1
Helmholtz-Zentrum Berlin, Germany / Niels Bohr Institute, Denmark, 2Delft University of Technology, The
Netherlands, 3European Spallation Source ESS AB, Sweden
We present an investigation of a SEMSANS[1,2] instrumental set-up where a spatial beam modulation is obtained
using triangular field coils.
Measurements were performed at the Reactor Institute Delft using a double-disk chopper system with a polarised
neutron beam and a time sensitive 3He tube detector behind cadmium absorption gratings of varying periodicity.
Measurements were compared to McStas simulations.
With a constant field in the triangular coils only neutrons with certain wavelengths will experience an amount of
Larmor precession that spatially modulates their polarisation to be synchronised with the grating. This is shown by
measuring with a broad wavelength range while scanning the spin echo condition, and it is clearly seen that a
polarisation is obtained at the expected wavelength (plus a weaker signal at twice this wavelength). The aim of the
investigation is to create the basis for a time of flight white beam set-up without gratings, where the fields in the
coils are ramped to match the varying energy of the neutrons in the pulse.
A complete SEMSANS set-up will be able to measure magnetic samples since the spin manipulation is performed
such that the mapping of the polarisation into a spatial modulation de-couples the scattering information from the
beam depolarisation in the sample. Moreover, these components built into a polarised SANS instrument can be
used to simultaneously measure the SANS and SESANS signal in order to obtain information on structures in the
range from 1 nm up till 100 micrometer[3].
[1]
[2]
[3]
W. G. Bouwman et al. Physica B 404, 2585-2589 (2009)
M. Strobl et al. J. Appl. Phys. 112, 014503 (2012)
W. G. Bouwman et al. Physica B 406, 2357-2360 (2011)
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P.112 Wide-aperture fan neutron supermirror analyzer of polarization for SNS magnetism reflectometer
V Syromyatnikov1, V Ulyanov2, V Lauter3, H Ambaye3, V Pusenkov2, A Gilev2, A Bulkin2, I Kuznetsov2 and E
Medvedev2
1
Petersburg Nuclear Physics Institute, Russia, 2B.P. Konstantinov Petersburg Nuclear Physics Institute, Russia, 3SNS,
Oak Ridge National Laboratory, USA
During the last years in PNPI it has been created two highly effective supermirror analyzers of polarisation of fan
type for neutron reflectometers REMUR (JINR, Russia) [1] and NeRo (GKSS, Germany) [2]. A new improved wide
aperture analyzer of polarization of fan type on the basis of polarizing supermirrors SwissNeutronics is created in
PNPI for neutron Magnetism Reflectometer (SNS ORNL, USA). The analyzer is installed in front of the two coordinate
position-sensitive detector with sensitive area 260x260 mm2. The neutrons with wavelengths from 2 to 12 Å are
used in reflectometer. The analyzer consists of 158 channels and its entrance cross-section is 120x240mm2. In the
paper the results of calculations and tests of the analyzer are presented.
[1]
[2]
Yu.V. Nikitenko, V.A. Ulyanov, V.M. Pusenkov, S.V. Kozhevnikov, K.N. Jernenkov, N.K. Pleshanov, B.G.
Peskov, A.V. Petrenko, V.V. Proglyado, V.G. Syromyatnikov, A.F. Schebetov, Nuclear Instruments and
Methods A 564 (2006) 395.
V.G.Syromyatnikov, A.F.Schebetov, D.Lott, A.P.Bulkin, N.K.Pleshanov, V.M.Pusenkov, Nuclear Instruments
and Methods A 634 (2011) s126.
P.113 BioRef 2.0 – Upgrading the capabilities of HZB’s ToF reflectometer
M Trapp1, M Kreuzer2, M Strobl3, R Dahint1 and R Dahint2
1
University of Heidelberg, Germany, 2Helmholtz-Zentrum Berlin, Germany, 3ESS
During the last year BioRef, HZB’s recently commissioned time-of-flight reflectometer has undergone a significant
upgrade.
The installation of an additional chopper extended the available wavelength resolution up to 11% at a constant
Δλ/λ. Recent results demonstrate the reduction in measuring time with that relaxed resolution which allows now for
the investigation of kinetic processes on a minutes time scale. In combination with in situ FTIR measurements
BioRef offers unique possibilities for soft matter and biological applications.
As an example the influence of polyelectrolyte solutions on the structure of solid supported lipid membranes, as
well as the effects of high hydrostatic pressure (1kbar) and shear forces on the membranes will be shown.
In addition, BioRef is currently being equipped with a bolt-on Spin Echo Resolved Grazing Incidence Scattering
(SERGIS) module for resolving lateral structures on nanoscale. The conceptual design of the add-on will be
presented and discussed.
P.114 Application of crystallographic methods to neutron reflectometry
Z Tun
Canadian Neutron Beam Centre, Canada
In the year following the Bragg Centennial, it is strange to ask if Bragg’s Law is deficient in any way. The answer is
yes – since refraction of X-rays at a crystal surface is not taken into account, the equation 2dsinq = nl contains a
systematic error. The error is extremely small in the case of diffraction from a typical crystal. Moreover, correction
for the error depends on the shape and orientation of the crystal. Therefore, ignoring the effects of refraction makes
perfect sense in our textbook derivation of Bragg’s law.
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However, refraction cannot be ignored if we wish to apply the methods traditionally used for solving crystal
structures to the analysis of neutron or X-ray reflectometry data. Since reflectivity is usually measured with a very
simple geometry (a slab sample in Bragg reflection configuration) directional changes of the beam due to refraction
can be taken into account exactly. Simulations show that correcting for this effect is very important. In some
special cases, this correction alone can lead to direct determination of the scattering-length density profile. The
profile thus obtained can be quite accurate. More importantly, data interpretation based on this method does not
depend on preconceptions concerning the layer structure of the material – no assumptions about the sample are
required.
This presentation is a sequel to a recent paper by Tun that describes the application of the Patterson method to
analyzing neutron reflectometry data.
[1]
Patterson analysis for layer profile determination by neutron or X-ray reflectometry, Z. Tun, J. of Appl.
Crystallography 45, 398-405 (2012)
P.115 TOFLAR, quasi-elastic neutron scattering combining time of flight and Larmor modulation
A van Well
Delft University of Technology, The Netherlands
In conventional time-of -flight instruments either the incoming or scattered beam is monochromatic, throwing away
a substantial fraction of the available neutron intensity. Furthermore, the choice of the monochromatic wavelength
determines the dynamic range. In the TOFLAR technique the complete wavelength spectrum is used, the wavelength
being labelled by Larmor precession. As a result, the neutron intensity is considerably higher and the dynamic range
is substantially wider. As a result of the modulation technique TOFLAR will be especially suited for quasi-elastic
scattering and less for determining low-intensity inelastic scattering. In this contribution a theoretical description,
including dynamical range (both in wavelength and energy transfer) and energy resolution will be discussed. The
results will be compared with McStas simulations.
P.116 The ESS reflectometry project
H Wacklin
ESS AB, Sweden
The ESS reflectometry project includes the study of several instrument concepts for two main types of
reflectometers: a horizontal reflectometer capable of measuring both liquid and solid interfaces, and a vertical
reflectometer with emphasis on polarisation analysis and small sample sizes, with all instruments types being
evaluated for their suitability to include off-specular, spin-echo and grazing-incidence components. In addition to
two reflectometers, a surface scattering instrument dedicated to grazing incidence SANS is considered.
P.117 Inelastic scattering on a neutron reflectometer: Is it worth it?
A Wildes
Institut Laue-Langevin, France
Neutron inelastic scattering is inherently limited by the relatively weak flux of current neutron sources. The signal is
proportionate to the number of atoms in the sample, and samples generally need to be relatively large to have
statistically significant count rates. Thus, the use of the technique to measure materials with inherently small
masses, for example thin films, multilayers, and superlattices, has hardly been pursued.
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The construction of new, high flux sources has raised the possibility that inelastic scattering might be measurable
from thin films, particularly in the total reflection regime where the strong enhancement in the scattering boosts
count rates. The accessible energy ranges at these momentum transfers are constrained by kinematic limits,
however. This presentation discusses these limits and the corresponding viability of using neutron reflectometers to
measure inelastic scattering. The results of tests using the D17 reflectometer at the ILL will be presented and
discussed.
ICNS 2013 International Conference on Neutron Scattering