ISIS SECOND TARGET STATION PROJECT
SANS
Beamline Name: SANS2a
External Coordinator 1:
Coordinator 2:
ISIS Contact:
Dr Adrian RENNIE
Dr Julian EASTOE
Dr Richard HEENAN
Department of Chemistry
School of Chemistry
ISIS Facility
King’s College London
Cantock’s Close
Room 1-21, Building R3
The Strand
University of Bristol
Rutherford Appleton Lab.
London, WC2 2LS
Bristol, BS8 1TS
Didcot, OX11 0QX
Tel: 020 7848 2534
Tel: 0117 9289180
Tel: 01235 446744
Fax: 020 7848 2810
Fax: 0117 9250612
Fax: 01235 445720
rennie@colloids.ch.kcl.ac.uk
julian.eastoe@bris.ac.uk
r.k.heenan@rl.ac.uk
Science Case:
The main design features of the Second Target Station, of enhanced cold neutron flux, broad spectral range and high
resolution, are particularly well suited for exploitation by Small Angle Neutron Scattering, SANS. The gains in
performance compared to the existing LOQ instrument will be spectacular, and will provide world leading SANS
instrumentation. It will open up new and exciting opportunities in the technologically relevant and emerging areas of
Soft Condensed Matter, Advanced Materials, and Biomaterials.
SANS is recognised as a powerful technique for determining microstructure in the dimension range of 10 to 5000 Å.
The LOQ SANS instrument at ISIS has been highly successful in pioneering the virtues of the white beam time-offlight method, the ability to access a wide range of scattering vectors, Q, (length scales) simultaneously with improved
resolution. The experimental programme that has developed on LOQ has resulted in a throughput and publication
record that is comparable with world-leading instruments.
In the areas of Soft Matter and Advanced Materials there are distinct trends towards the study of complex multicomponent or multi-phase systems, and non-equilibrium systems as well as the use of complex environments. In many
such systems the dimension scales of importance range from the molecular to the mesoscale, dictating a need for a wide
Q range. Kinetic studies, ranging from chemical reactions to probes of self-assembly, require a broad spectral range
and high flux. Multi-component and multi-phase systems are only tractable with the parametric studies possible with
high flux and good resolution. Furthermore our ability to study a broad range of biomaterials will be transformed,
where complexity, weak scattering from dilute systems, and an emphasis on the longer length scales are all key issues.
Hence the main features of SANS on the Second Target Station that are important are:
−
Using the wide wavelength range available at 10 Hz, the white beam time of flight method will provide a
uniquely wide simultaneous Q range.
−
The optimised grooved coupled cold moderator together with other improvements in neutron optics and
detectors will provide overall count rate gains of typically 30 – 40 compared to LOQ, to give world class
performance.
−
Longer flight paths will provide an enhanced low Q performance, and flexibility in the Q range to suit
individual experiments.
−
Good Q resolution compared to reactor instruments.
−
Improved signal / noise.
Given the scientific importance of SANS and the sheer size of the potential user base there is an opportunity for the
ISIS second target station, in common with other world class facilities, to provide two SANS instruments from the
outset. SANS2a and SANS2b would be optimised for performance at low and intermediate-to-high Q respectively.
The SANS2a instrument is optimised to reach smaller Q values, with conventional pinhole collimation, than has
previously been achieved at a pulsed neutron source. Its longer collimation length maximises count rates in the
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SANS
important region between Q = 0.001 and 0.002 Å-1 (d spacings to 5000 Å), but at the expense of a small reduction in
neutron wavelength band due to frame overlap and inelastic background considerations with a longer beam line.
The general themes of the science case for both instruments are naturally very similar and so will only be given
once below. More specific examples are given separately for each instrument. SANS2a is specifically mentioned
below in some of the areas of science where it is likely to have a particular advantage over SANS2b.
Soft Condensed Matter
Soft Condensed Matter encompasses a wide range of molecular materials, from polymers and surfactants, to colloidal
suspensions, thermotropic liquid crystals, lyotropic mesophases, and micro-emulsions. All are important in the context
of applications in household products, personal care products, lubrication oils, adhesives, protective coatings, drug
delivery systems, the development of green solvents, and enhanced oil recovery.
The ability to manipulate refractive index, through H / D isotopic substitution, allows complex multi-component or
multi-phase systems, to be studied. H/D contrast variation also allows interfacial structures to be highlighted,
particularly to obtain polymer density profiles on particles and emulsions droplets, an area which greatly benefits from
wide Q range and high flux.
The penetrability of cold neutrons makes the use of a range of complex environments (pressure cells, flow cells,
rheometers) more tractable. These features coupled with the ability to simultaneously probe a wide range of length
scales with substantially enhanced flux will open up exciting new opportunities in the study of Soft Matter and
Complex Fluids. Real time experiments on, for example, in-situ synthesis of polymers or colloids requires both high
flux and a wide simultaneous Q range.
Extensive parametric studies (the need to make measurements over a wide variety of conditions; such as isotopic
labelling, temperature, pressure, external force field, pH, concentration, composition and so on) in complex systems will
be possible with better resolution, in shorter times, on more dilute samples, and with more detailed isotopic labelling
schemes. The ability to measure, say, changes in polymer radii-of-gyration associated with shape changes on short
timescales will provide new insights into the mechanisms behind the conversion of chemical energy into mechanical
motion in molecular machines.
Rapid Screening of the Mesoscale Structure of Novel Multi-Component Materials
More complex multi-component systems, often more closely resembling industrially relevant materials, provide the
opportunity to investigate the critical role of minor components. SANS2a would be useful for studying phase
separation and interactions in colloidal systems involving larger particles and droplets.
More complex environments will become possible, more relevant to the conditions faced in different processing routes
as, for example, in the extrusion of polymers or the extensional shear of colloidal solutions. The smaller Q on SANS2a
is relevant for studies of the conformation and phase separation of high molecular weight polymers and block
copolymers. The molecules are large but phase separation can occur on even longer distance scales.
Measurements of time-dependent processes will open up poorly explored fields such as the dynamics and kinetics of
surfaces, thin films and anisotropic systems of polymeric and surfactant origin including the nanoscale details of
complex rheological behaviour.
Flow, Deformation and Processing
The processing of soft solids in many important industrial processes involves flow, from component mixing in pipe
flow, to extensional flow for alignment by extrusion. The flux available on the Second Target Station will make it
possible to study the mechanisms controlling these processes at a macromolecular level in realistic conditions and
geometries. Measurements of polymer melts with D / H labelling under flow will develop the structure-rheology
relationships in polymer processing and address the role of features such as branching, polydispersity and additives.
Similar labelling schemes will be exploited in multi-component systems, involving surfactants, polymers and colloidal
particles, to provide links between phase behaviour, rheology, and product formulation and stability. The enhanced flux
will enable smaller beam sizes to be used, and spatial variations in microstructure and flow properties to be explored.
Deformation of the structure of solid polymers during elongation, compression or creep could be studied in real time.
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The increased flux would make possible studies of in-plane phase separation within deuterium labelled, spun coated
polymer films as thin as 500 Å.
Self-Assembly and Colloidal Interactions
Self-assembly, involving lyotropic mesophases, micro-emulsions and vesicles of surfactants, lipids or amphiphilic block
copolymers, is of interest in a wide variety of fields such as product encapsulation, extraction processes and multi-phase
reaction media. The increased flux available on the Second Target Station will enable the dynamic processes associated
with structural phase changes, association and dissociation to be studied. For example, the study of coexisting
micellar / liposomal phases and their evolution with time, the co-existence of colloidal or micellar / lyotropic phases and
their role in phase stability, and polymer-surfactant mixtures.
At smaller Q values SANS2a would be very powerful at probing areas such as the dynamics and structure of large self
assembled systems like vesicles, and “living polymer” rod-like micelles as well as the interaction of droplets or particles
with polymers or surfactants. Many complex systems in these areas are relevant to industrial problems and though light
scattering has a role, neutron contrast variation is crucial to obtain the desired information. SANS2a would have a
useful overlap in Q with both USANS and light scattering.
Aggregation and self-assembly in supercritical fluids, such as CO2, and new ionic liquids, are now important areas for
the development of safe alternative solvents in flavour extraction, dry cleaning, controlled polymerisation and
potentially many other processes. In-situ pressure cell studies over this broad area will be greatly facilitated as the
scattering contrast against CO2 is often weak.
Biomolecular Materials
The Life Sciences are likely to be the growth area of the future, with many health-related issues underlying this
importance. In a broader context of the biological remit, in for example the fields of pharmacy, food science, sensors,
biocompatibility and biofunctionality, there is much similarity with problems in Soft Matter, and SANS is poised to
make a significant impact. In the last UK Technology Foresight exercise, in the areas of Health and Life Sciences,
Food and Drink, Agriculture, and Natural Resources and Environment, priorities in drug preparation and delivery,
pharmaceuticals, metabolic pathways, immune manipulation, material changes during processing, and pesticides, are all
closely linked to understanding membrane structures, membrane-protein interactions, the structure of macromolecular
complexes, aggregation in gels and emulsions, surface adsorption and structure, self-assembly, biocompatibility, and
biofunctionality. The enhanced capabilities of SANS, especially SANS2a, on the Second Target Station will greatly
expand the contribution that ISIS can make in these areas. Importantly the size and conformation of membrane proteins,
which are not easily crystallised, may be examined by SANS, using solvent contrast variation to remove contributions
from stabilising surfactants or membrane fragments.
A newly emerging area is the development of synthetic artificial biostructured materials (bioengineering) for
applications such as bone or tissue replacement. The need to understand the microstructure from molecular to
mesoscale and macroscopic dimensions in such materials is central to development in this area, where bioactive and
degradable materials are replacing conventional polymers and cements. These complex structures may include drugs,
proteins or DNA. Again SANS2a will be useful to probe opaque structures heading towards micron length scales,
where other techniques start to become accessible.
Macromolecular Assemblies
Low resolution studies, using SANS, are already established as an important method for characterising the tertiary
conformation and functionality of macromolecular assemblies or complexes, where only the detailed crystalline
structure of fragments or components is known, not the overall configuration. The importance of larger complexes,
such as the binding of antigens to large antibodies and the link between protein folding / unfolding and the formation of
fibrils in amyloid-based disorders (Parkinson’s, HIV, Alzheimer’s) stresses the need for mesoscale structural
information. Extending pulsed source SANS to lower Q on SANS2a, whilst maintaining a wide simultaneous Q-range,
will provide an exciting opportunity for neutron scattering to probe larger proteins, biomolecular complexes and viral
fragments with improved spatial resolution. Deuterium labelling is a key technique in this area which needs the highest
possible flux in order to obtain good results in mixed H2O / D2O solvents with small SANS signals and large incoherent
backgrounds. SANS2a will also improve understanding of long-range structure or conformation in protein folding
problems, materials such as polypeptide tapes, and amyloid plaque formation. Studies of the interaction of
macromolecules with smaller entities such as surfactant micelles, lipids, polymers will also benefit from a wide
simultaneous Q range and high flux.
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SANS
Pharmaceuticals
In pharmaceutical applications, structural information from SANS may be exploited in the design and optimisation of
systems for drug encapsulation and delivery. This again has much in common with many aspects of colloid science and
self-assembly. An important area which requires new approaches to drug delivery is that of ‘gene therapy’. SANS has
an important role to play in the broader context of drug functionality, in understanding the interactions of drugs or
proteins with membrane structures. Many successful drug delivery schemes involve water-soluble polymers. Wide Q
range SANS is the ideal method to study not only size but also the density profiles of such systems, with the Second
Target Station allowing a wider range of sizes and more extensive parametric studies (changing concentration,
temperature, salt etc.).
Food Science and Technology
Although practical systems in food science are extremely complex, SANS will permit the study of solvent distribution
and material changes (denaturing) during processing, and considerable progress can be made using relevant model
systems. Understanding kinetics is central to areas such as the control of food colloid stability, foam or gel formation,
or protein fouling of filters during processing. The smaller Q’s accessible on SANS2a will help to make a wide range
of these in-situ kinetic and structural studies accessible for the first time and help validate existing mesoscale
computational models.
Advanced Materials
The characterisation of Advanced Materials using neutron scattering, including new magnetic materials, ceramics,
composites, metal alloys, nanoscale structures, complex materials such as zeolites or templated silicates and novel
electrolyte materials, generally requires wide-angle diffraction methods to examine structure at the molecular level.
However, many such materials also have hierarchical structures which extend their diffraction patterns into the SANS
range. Neutron diffraction from synthetic polymer fibres is currently an under exploited field which will benefit from
increases in flux and Q range on SANS2b, as would studies of polymer crystallisation.
Several areas would particularly benefit from the smaller Q’s on SANS2a. High flux SANS, coupled in appropriate
cases with H / D or other contrast variation, is a powerful technique to study nucleation and growth processes involved
in the formation of many advanced materials. These include solid growth from solids (precipitates), solids from liquids
(crystallisation), liquids from liquids (phase separation), pre-nucleation, and hydro-thermal synthesis of cements. The
ability to accommodate complex sample environments makes it possible to study many of these processes in-situ.
There are many questions which SANS2a would help to answer, such as whether in-situ structures are the same as those
of dried or calcined samples.
In other areas such as ceramic coatings on turbine blades, concretes, metals under creep, and irradiation-induced
embrittlement in nuclear plant grade steels, high flux SANS is able to study the formation of cracks and voids. There is
potential to greatly expand the use of SANS by the UK engineering materials community, for whom a large sample
space to install and position components such as a 200 kg stress rig will be an important feature. Examination of very
low concentrations of quite large defects in single crystal silicon, of great importance to the semi-conductor industry, is
possible due to the fortuitously low adsorption of neutrons allowing extremely thick samples to be used.
Metallurgy
SANS has the advantage of averaging over large sample volumes to see low concentrations of small voids, precipitates
and defects not easily quantified by conventional methods. Methods of annealing or recrystallisation may be studied insitu. Understanding precipitation hardening in new generations of Ni based superalloys, critical for high temperature
turbines, will require both SANS and crystallographic neutron diffraction.
Observation of creep cavitation in pressure vessel steels would benefit from any extension of high flux SANS to low Q
on SANS2a. When voids are not much larger than micron sized they are strength limiting and the component is no
longer reliable. Higher flux would improve spatial resolution and allow in-situ time resolved studies.
The interaction of hydrogen with dislocations requires the small Q of SANS2a to see the arrangement of the
dislocations coupled with higher Q studies on SANS2b for the trapped hydrogen at dislocation cores, both with very
high flux due to weak signals.
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Magnetic Materials
Neutron scattering has revealed essentially everything that is known about magnetic structures. SANS is able to
contribute to investigations of the structures of magnetic domains and the flux line lattice, magnetic colloidal particles,
and nano-structured materials with novel magnetic properties.
Studies of lateral magnetic correlations and structure in patterned media, proposed as new generation high density
recording media, will provide a challenging and significant role for SANS. The increased flux from Target 2 will
enable world-class contributions to be made at ISIS.
Outline Design Specification: SANS2a
Chopper
Bender
Sample
Movable
Detector
Removable Guides
The design for SANS2a proposed here (and summarised in Table 1 below) gives gains of typically 30 – 40 over LOQ,
and wider simultaneous Q ranges, coupled with the flexibility of a moving detector to match the overall Q range to a
given experiment. The coupled, grooved, cold moderator of the Second Target Station gains a factor of 15-20 in flux
per proton at the longer neutron wavelengths crucial for SANS at small Q. The smaller, grooved, moderator is well
suited to SANS since it increases count rates at longer sample-detector distances due to the small area of moderator
viewed by the pinhole collimation used in SANS. Lower pulse repetition rates and an m=3 (i.e. 3×θcNi ) super-mirror
bender will allow a wide band of simultaneous wavelengths, typically 1.5 to 12 Å (cf. 2.2 to 10 Å on LOQ), improving
count rates and Q range. Further gains accrue due to larger detectors and improved neutron optics. Combined with a
300 µA proton current these factors more than offset the reduction in repetition rate from 25 to 10Hz to give total count
rate gains of from 20 up to several orders of magnitude compared to the present LOQ.
To further expand the Q range the movable 1m square multi-wire gas detector may be shifted sideways by at least
300mm. Extended flight paths partly compensate for the longer time spread of a coupled moderator so as to maintain
excellent Q resolution compared to reactor sources (except at the smallest Q values where sample size and detector
resolution dominate and resolution is always comparable). Typical Q ranges, relative count rates from numerical and
Monte-Carlo calculations, and mean resolution data are given in Table 2 and Figure 1.
To reach a minimum Q of 0.001 Å-1 a sample-detector distance L2 of around 22m is required. The normal optimisation
conditions then suggest a matching incident collimation distance from the neutron source. Situating the sample at 25m
from the moderator provides a good compromise with a 48 m long beam line since a possible 100 msec prompt spike
does not then overlap important data. With a detector at 47m (L2=22m) SANS2a could with λ=3.0 to 10 Å access
Q~0.001 to 0.09 Å-1, and to further enhance the scattering at very small Q, it could use λ=6.75 to 12 Å for Q~0.001 to
0.04 Å-1. The wavelength ranges here are restricted both by frame overlap and the need to avoid inelastic scatter from
the previous frame swamping the long wavelength signal. Background suppression by the bender and shielding should
be sufficient to avoid having to mask out any prompt spike background at 100 msec, λ=8.4 Å. Experiments requiring a
wider Q range and the lowest Qmin on SANS2a could run with a wider λ band at 5 Hz rather than 10 Hz. At a “middle
distance” of say L2=12 m SANS2a could use λ=1.5 to 10.7 Å, to access a broader Q range.
The sample area will be as large as possible with side access at floor level in order to wheel in sample environment
equipment and reduce set up time. An easily adaptable final collimation section and large space will also allow for
temporary installation of spectroscopic and other equipment for the application of different techniques simultaneously
with SANS. An accurate positioning table to take equipment up to 200 kg in weight will be required.
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Table 1
Moderator
Coupled cold
Incident Wavelengths
1.5 – 14.6 Å at 27 m; 3.0 -10 Å or 6.75 -12 Å at 47 m
Q Range
-1
Flexible e.g. with detector 300mm offset: ~ 0.001 to 0.09 Å at L2 = 22 m; 0.002 to 0.32
-1
Å at L2 = 12 m
L1, L2
Moderator-Sample: 25m, Sample–Detector: 2 to 22 m
Flight Path
Ni
3θc super-mirror bender; removable, plain Ni guide sections for variable collimation
length; evacuated
Choppers
Variable-phase counter-rotating double-disc (at ~6.5 m, 10 Hz or 5 Hz)
Detectors
At least 1 m x 1 m position-sensitive, 5 mm pixel size; movable in vacuum tank, with
sideways offset
Beam Size
6 to 15 mm diameter at sample
Detector Tank
22 m long; evacuated; with good shielding
Sample Environment
Large, side-access sample area to take a wide variety of equipment for in-situ
measurements; in air, but with option for evacuated sample position; all standard SE
equipment (sample changer, shear cells, magnet, cryostat, etc.)
Table 2
Lcoll
(m)
L2
(m)
λmin
(Å)
λmax
(Å)
Qmin
(Å-1)
Qmax1
(Å-1)
Qmax2
(Å-1)
2
2
1.5
12 -14.6
0.013
1.38
1.80
4
4
1.5
12 -13.6
0.006
0.71
0.95
12
12
1.5
10.7
0.002
0.24
0.32
18
22
3.0
10.0
0.001
0.066
0.088
Running at 5Hz could increase Qmax at the
expense of count rate
18
22
6.75
12.0
0.001
0.029
0.039
More flux at smallest Q from longer λ
Comments
NOTE: Lcoll is the collimation length. Qmin is calculated for λ=10 Å, though at shorter distances one might routinely use
out to 12 Å, and for samples with suitably high transmission, perhaps as far as 14.6 Å (as indicated in the λmax column).
Qmax1 is for the diagonal of the square detector when centred on the beam axis, Qmax2 is with the detector offset by
300 mm. At L2=22 m the SANS2a λ range is restricted by both frame overlap and fast inelastic scatter from the previous
frame.
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Count Rate (arb units)
2m
4m
12m
22m
Q(Å-1)
Figure 1a
Approximate relative count rates for a “flat scatterer” on
SANS2a. (upper blue line) L2=2 m, (red line) L2=4 m,
(middle blue line) L2=12 m (all with λ=1.5-10.7 Å),
(lower blue line) L2=22 m (λ=3-10 Å), and (red +)
L2=22 m (λ=6.75-12 Å). Also shown are an
approximation to the current LOQ (cyan † , using
λ=2.2-10 Å), and also a “reactor” instrument with a 10%
velocity selector and 10 times time average flux of the
ISIS Second Target (i.e. similar to D22 at the ILL);
(upper black dashed line) L2=4 m with λ=6 Å and
(lower black dashed line) L1=18 m and L2=22 m with
λ=10 Å.
Except for LOQ all calculations assume a 1m square
detector displaced horizontally by 300 mm.
Figure 1b
The estimated mean Q resolution as the FWHM (full
width half maximum) of the distribution. (right blue
line) L2=2 m, (red line) L2=4 m, (middle blue
line) L2=12 m (all with λ=1.5-10.7 Å), (left blue line)
L2=22 m (λ=3–10 Å), and (red +) L2=22 m (λ=6.7512 Å). Also shown are (cyan †) an approximation of
the current LOQ (using λ=2.2-10 Å), and a “reactor”
instrument with a 10% velocity selector (i.e. an
instrument similar to D22 at the ILL); (right black
dashed line) L2=4 m with λ=6 Å and (left black
dashed line) L1=18 m and L2=22 m with λ=10 Å.
The effective resolution on SANS2a at middle Q is
actually better than shown due to a sharper peak in the
resolution function from long λ values over broad tails
from short λ values.
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Beamline Name: SANS2b
External Coordinator 1:
Coordinator 2:
ISIS Contact:
Dr Adrian RENNIE
Dr Julian EASTOE
Dr Richard HEENAN
Department of Chemistry
School of Chemistry
ISIS Facility
King’s College London
Cantock’s Close
Room 1-21, Building R3
The Strand
University of Bristol
Rutherford Appleton Lab.
London, WC2 2LS
Bristol, BS8 1TS
Didcot, OX11 0QX
Tel: 020 7848 2534
Tel: 0117 9289180
Tel: 01235 446744
Fax: 020 7848 2810
Fax: 0117 9250612
Fax: 01235 445720
rennie@colloids.ch.kcl.ac.uk
julian.eastoe@bris.ac.uk
r.k.heenan@rl.ac.uk
Science Case:
Given the scientific importance of SANS and the sheer size of the potential user base there is an opportunity for the
ISIS second target station, in common with other world class facilities, to provide two SANS instruments from the
outset. SANS2a and SANS2b would be optimised for performance at low and intermediate-to-high Q respectively.
SANS2b represents a new concept for small angle scattering by aiming to maximise either count rate or Q range using
two (or more) state-of-the-art 1 m square multi-wire gas detectors. These detectors will be freely movable within a very
large rectangular vacuum tank. With a 13 m long vacuum tank an unsurpassed simultaneous Q range of around
0.002 Å-1 to beyond 3 Å-1 could be obtained with one detector at 12 m and the other, offset, at 2 m.
The general themes of the scientific case for SANS2b are the same as those for SANS2a and so will not be repeated
here. Coupled with the increased flux of Target 2, SANS2b will provide unique opportunities, in a wide range of
scientific areas:
−
With the detectors at different distances, ordering or Bragg peaks may be monitored at high Q simultaneously
with SANS at small Q. This is particularly important for polymer, sol / gel and other systems undergoing
crystallisation.
−
Conversely in other systems long-range phase separation may produce ordering or Bragg peaks at small Q
whilst changes in more local structure or conformation are followed at high Q. This will be particularly
important for studies of polymer processing.
−
Fibre diffraction requires the widest possible simultaneous Q range to follow all levels of what are often
hierarchical structures ranging from intermolecular distances to micron sized voids and phase separation. For
example in nylon-6 fibres the lamellar peak is at Q ~ 0.08 Å-1 whilst a series of crystal peaks are between 0.8
and 1.7 Å-1, each of which subtly changes with chemical environment.
−
Accurately corrected data over a significant Q range will increase confidence in the use of Fourier transform
methods of data analysis where direct modelling is not possible, or the use of invariant integrals to estimate
phase volumes independent of actual scattering laws. Direct calibration of both high and low angle detectors in
the main beam is an important feature of SANS2b which will particularly help these types of analyses. Data
inversion is becoming important in detailed studies of copolymers, micelles and other complex solution
structures, in addition to its more established use for biomolecular solutions. Invariant integrals have been used
for fibre diffraction, particularly by X-rays, but again could be more widely applied.
−
Higher count rates may be achieved over all but the smallest Q’s by placing the two detectors at similar
distances to expand detector solid angle. This would be a particular advantage for anisotropic systems, for
example those perturbed by shear or stretch.
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Soft Condensed Matter
The local interaction of polymers or surfactant micelles with much larger particulate dispersions or emulsion droplets is
an important area of study related to many industrial products where neutron contrast variation is used to highlight
interfacial structure. A wide Q range and high Q to study local conformation and interactions are essential.
Membranes and vesicles require an extremely wide Q range to follow both vesicle diameters at low Q simultaneously
with wall thickness, or multi-lamellar Bragg peak scattering, or even details of surfactant molecular conformation at
high Q.
Studies of clays and vermiculites often require Q ranges spanning the region between conventional small angle and
wide-angle diffraction; SANS2b easily provides such a range.
Liquid crystals are again anisotropic scatterers that would benefit from an extremely broad Q range: very high Q to
study intramolecular conformation simultaneously with intermediate Q for intermolecular ordering and low Q for longrange structure and domain size.
Biomolecular Materials
Conformational studies of biomolecular complexes require extremely high quality data at high Q to improve the
resolution of dummy atom / residue models.
Studies of bone and collagen would benefit from simultaneous low and high Q capabilities of SANS2b.
Advanced Materials
Time resolved studies of the self assembly of surfactant templated inorganic materials, such as zeolites and silicalites,
would benefit greatly from being able to see a series of peaks from ordered mesophases at high Q whilst following
aggregate size at low Q.
The interactions of hydrogen with carbon nanotubes requires high flux, a wide Q range going to high Q and deuterium
contrast variation to produce meaningful results, SANS2b would be ideal.
Complex systems with hierarchical structures would in general be better resolved, using the advantages of D / H
contrast variation, coupled with the high flux and unsurpassed simultaneous Q range of SANS2b.
To distinguish between spinodal decomposition or nucleation plus growth mechanisms of real time precipitate
formation in say semiconductors or metal matrix composites requires a high flux and extremely wide Q range, since the
one process has long range concentration fluctuations whilst the other has short range aggregation.
Outline Design Specification: SANS2b
Chopper
Bender
Sample
Movable
Detectors
Removable Guides
The initial incident beam for SANS2b is the same as for SANS2a, with a super-mirror bender to reduce fast neutron
background, removable guide sections to match the incident collimation length L1 to sample-detector distance L2 but the
sample is now at 19 m from the moderator (and not 25 m). The design is summarised in Table 3.
Though an arc of fixed “high angle” detectors around the sample position can access an extremely wide Q range out to
high Q such approaches are fraught with difficulties. For example such a detector geometry is best suited to cylindrical
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and not “flat plate” samples and does not deal easily with anisotropic scattering. More importantly it is extremely
difficult, if not impossible, to reliably calibrate fixed detectors close to the sample. SANS2b will have freely movable
1 m square detectors with a closest sample-detector distance of ~2 m, which maintains adequate Q resolution with a
~5mm detector pixel size. The rectangular section vacuum tank would have internal dimensions ~3 m wide x 2.5 m tall
x 13 m long. The vacuum tank would be like an inverted ship’s hull, with integral borated wax shielding, bolted to the
floor.
The two separate 1 m square position-sensitive detectors, with adjustable height, could be positioned anywhere within
the vacuum tank to give L2 in the range 2 to 12 m. This could be achieved either by remotely controlled trolleys on a
smooth floor or, more likely, with moving “crane gantries” running on rails, which would allow shielding of the floor
area. Intermediate baffles will ensure that the detectors only view the sample. Both detectors would be equipped with a
movable beam stop to enable each to be calibrated with the same standard sample in the main beam. This would
remove most of the calibration difficulties encountered with the fixed “high angle bank” detector approach. The latest
large area multi-wire gas detectors have their position encoding electronics in air on the rear of the detector. Thus only
simple air flow and return hoses containing a few power and signal leads are required to each detector.
For safety in the event of a beam vacuum window breakage fast acting shutters or inflatable air bags (as used in cars)
inside the tank will be considered as a means of reducing damage and slowing the air in-rush. A beam vacuum window
of about 14 cm diameter at 5 cm from the sample would suffice. Some standard types of sample environment
equipment would require modification to enable them to use the full range of scattering angles. Else wise a large area
for sample environment access is anticipated, as for SANS2a, with maximum flexibility to adapt to a wide range of
sample environment types.
The sample would be at 19 m at which the 13º angular separation of adjacent beam lines gives a ~4.4 m space for the
front part of the vacuum tank and its shielding, though negotiation with adjacent instruments will be required since the
tank is slightly off-centre relative to the beam.
SANS2b would allow an even wider simultaneous Q range than SANS2a by combining two different sample-todetector distances (with the collimation length L1 optimised for either count rate at high Q or for Q resolution at small Q
to suit the science involved), see Table 4. Alternatively, with the two detectors at similar sample-detector distances, the
count rate could be doubled in all but the smaller part of the Q range. With λ=1.5Å the maximum Q in the horizontal
direction would be in excess of 2.5 Å-1 and more on the diagonal, allowing good overlap with “wide angle diffraction”
and the monitoring of ordering peaks simultaneously with the measurement of the SANS signal. Note that due to using
a broad wavelength range a continuous angular coverage is not required for the two detectors to overlap in Q.
Although some engineering challenges are presented by this design SANS2b is clearly feasible on the basis of existing
technology and would represent a significant step forward from the way SANS is traditionally performed!
Table 3
Moderator
Coupled cold
Incident Wavelengths
1.5 – ~15 Å at 21 m; 1.5 - 12.7 Å at 31 m
Q Range
Extremely flexible in range 0.002 to >2.5 Å
L1, L2
Moderator-Sample: 19 m, Sample–Detector: 2 – 12 m
Flight path
Ni
3θc super mirror bender; removable, plain Ni guide sections for variable collimation
length; evacuated
Choppers
Variable-phase counter-rotating double-disc (at ~6.5 m, 10 Hz or 5 Hz)
Detectors
At least two 1 m x 1 m position-sensitive, 5mm pixel size; freely movable horizontally &
vertically in vacuum tank
Beam size
6 to 15 mm diameter at sample
Detector tank
Rectangular ~3.5 m (wide) x 2.5 m (high) x 13 m; evacuated; with good shielding
Sample environment
Large, side-access sample area to take a wide variety of equipment for in-situ
measurements; in air, but with option for evacuated sample position; all standard SE
equipment (sample changer, shear cells, magnet, cryostat, etc.)
-1
SANS2b- Page 3
ISIS SECOND TARGET STATION PROJECT
SANS
Table 4
Lcoll
(m)
L2
(m)
λmin
(Å)
λmax
(Å)
Qmin
(Å-1)
Qmax1
(Å-1)
Qmax2
(Å-1)
Comments
2
2
1.5
15
0.013
n/a
>2.5
Both detectors at 2 m
12
12
1.5
12 -12.7
0.002
0.24
0.32
Detector 1 at 12 m
2
2
1.5
12 -15
0.15
n/a
>2.5
Detector 2 at 2 m
Count Rate (arb units)
NOTE: Lcoll is the collimation length. Qmin is calculated for λ=10 Å, at 2xRpenumbra, though λ to 12 Å should be routinely
used, and for samples with suitably high transmission, perhaps as far as 15 Å (as indicated in the λmax column). Qmax1 is
for the corner of a detector centred on the beam axis, Qmax2 is with the centre of Detector 1 offset horizontally (-300,0)
mm and Detector 2 offset diagonally (900,900) mm. The maximum offset could be about (1300,900) mm.
2m
12m
2m
12m collim
Q(Å-1)
Figure 2a
Approximate relative count rates on SANS2b, λ= 1.5 12 Å (red lines) one 1 m square detector at L2=12 m,
offset 300 mm, the other at L2=2 m, offset (900,900)
mm. (Note: this is not the maximum offset, so still
higher Q values are possible), and (green {) with both
detectors at L2=2 m, dashed lines show the two separate
detectors displaced (300,300) and (900,900) mm
respectively. Also shown are (cyan †) an
approximation of the current LOQ (using λ=2.2-10 Å),
and (black dashed line) a “reactor” instrument with a
10% velocity selector and 10 times the time average
moderator flux of the ISIS Second Target (i.e. an
instrument similar to D22 at the ILL) with L2=4 m
and λ=6 Å. Note the improved resolution of the high Q
detector at 2 m when using 12m of collimation (but ~36
times less flux).
Figure 2b
The estimated mean Q resolution as the FWHM (full
width half maximum) of the distribution. (red lines)
one 1 m square detector at L2=12 m, offset 300 mm, the
other at L2=2 m, offset (900,900) mm, and (green {)
with both detectors at L2=2 m displaced (300,300) and
(900,900) mm respectively. Also shown are (cyan †)
an approximation of the current LOQ (using λ=2.210 Å), and (black dashed line) a “reactor” instrument
with a 10% velocity selector (i.e. an instrument similar
to D22 at the ILL) with L2=4 m and λ=6 Å.
The effective resolution on SANS2b at middle Q is
better than shown due to a sharper peak in the resolution
function from longer λ values over broad tails from
short λ values. Sample size here is 10mm, resolution
could be improved further at high Q with tighter
collimation, at the expense of count rate.
SANS2b- Page 4