Appendix B: UK-CRG High Flux Diffractometer – Technical
Summary
The UK-EPSRC has recently invested heavily in instrument upgrades at ILL, which will benefit all
European scientists. We propose to capitalise on the new techniques developed with this investment, to
provide a unique high flux CRG diffractometer for the UK community. This machine will use a detector of
the type developed for the EPSRC-D19 project, a supermirror guide constructed as part of the EPSRC
Strain Imager project, a large focussing monochromator and software developed for the EPSRC-D2B
project. This new UK-CRG diffractometer will be comparable to D20 for flux, and to D1A for resolution
but will also be used like D19 for single crystals. Being in the guide hall, with tight radial collimation, it
will have very low background. As such, it will be ideal for the study of the chemistry and physics of new
materials, often available in only small quantities, for isotopic samples, materials under high pressure
and materials with long d-spacings. It will be possible to obtain beam time at very short notice, and UKCRG staff at ILL will provide an important “pied-a-terre” for the participating UK research groups.
Collaborative Research Groups (CRGs)
CRGs are a cost-effective way of using the existing European high flux neutron source. Already more
than a dozen CRGs have been set up by the French and German Associates, and even the smaller member
countries (Italy, Spain etc). The big attraction is that the ILL neutron source is free, and the marginal cost
is essentially manpower – two postdoctoral scientists plus a technician on short-term contracts – apart
from some initial capital investment and relatively small operating costs.
These obvious benefits have even permitted the French Associate to close down the local medium flux
reactor, with considerable saving, replacing it by a number of superior CRG machines operated by a
smaller number of staff. New CRGs are still being constructed, notably by the Italian partner, who
otherwise contributes 5% to the ILL budget.
Yet the UK Associate, whose contribution will increase in 2004 to 33%, has so far been excluded from
CRG participation. UK members of the ILL Steering Committee, led by Dr D. Schildt, have quite
naturally asked that CRGs be opened to new partners, and the ILL has responded by calling for new
proposals (without financial commitment), with a deadline of 10 October: http://www.ill.fr/Events/CRG/
The Proposal
We propose to capitalise on recent EPSRC project spending at ILL to construct a high flux UK-CRG
diffractometer, that could be used for both powders and single crystals, as follows:

Use the D19 project detector development to provide a large 2D detector for single crystals

Use the Strain Scanner project’s super-mirror guide H22 to provide a high flux position

Use the D2B project’s electronics, monochromator and data analysis techniques to provide high
efficiency at good resolution for powder diffraction
The inherent advantage of a continuous neutron source like that of ILL is the high time-averaged neutron
flux on the sample, more than an order of magnitude greater than on existing pulsed sources. The success
of instruments on a relatively weak source such as ISIS has been obtained by heavily investing in big
detectors. We plan to follow that lead by installing similarly large detectors on reactor instruments, which
combined with the much higher neutron flux at the ILL, will result in a uniquely powerful and flexible
instrument.
1
Our proposal then calls for a detector with a solid angle comparable to that of GEM, and x4 times larger
than that of D20. This is possible thanks to the UK-EPSRC investment in the new D19 project (Durham
University consortium). In fact two detector blanks have been made for the D19 project; we propose to
use the second one for the new UK-CRG. The cost of this new detector, which will be the main part of the
capital cost of the project, can thus be reduced to 700K sterling.
As part of the EPSRC Strain Imager project, the H22 guide will be replaced by a super-mirror guide,
which will greatly increase the neutron flux. The new strain imager will be placed behind D1A/D1B, so
freeing the first position on the guide now occupied by D1A. Together with slightly lower take-off angles
(around 90o for high pressure experiments) and a large focussing monochromator (released from the D2B
project), the flux on the UK-CRG sample position should exceed 107 n.cm-2.sec-1, considerably greater
than that on GEM, and even approaching that of D20. Situated in the ILL guide hall, with fine radial
collimation, it will have very low background, and will be ideal for very small samples. According to
Jorgensen et al.1 the efficiency of comparable machines is simply the product of the time averaged flux,
the sample volume and the detector solid angle. The new UK-CRG will then be a world-class machine for
work on small samples, as shown in table 1 (*GEM numbers are from P. Radaeli et al.2).
1.
2.
Jorgensen, J.D., Cox, D.E., Hewat, A.W., Yelon, W.B. (1985) Nuc.Inst.Meth. B12, 525-561.
Paolo G. Radaelli, Alex C. Hannon and Laurent C. Chapon (2003) Neutroni e Luce di Sincrotrone 8, 19-34.
ILL-D20
Time averaged sample flux
Relative sample volume
Detector solid angle (sr)
5x107
1
0.27
UK-CRG
ISIS-GEM1
107
1
1.00
~2x106
1
4.0
Table.1. The three parameters determining the speed of diffractometers with comparable resolution (Jorgensen et al. 1)
Specifications of the UK-CRG Diffractometer
Super Mirror Guide: thermal, M=2
Incident Divergence: 40’ (cf 35’ for D2B high flux mode)
Monochromator: Ge 300mm high, vertically focusing
Take-off Angle: 60o, 90o or 120o , with 90o used for high pressure sample environments.
Wavelengths: A large choice, for example at 90o take-off, three d-spacing ranges would be covered within
the limited scattering angle 2= 60o to 120o when using a high pressure cell.
[115] -> 1.54 Å;
[113] -> 2.44 Å; (graphite filter)
[111] -> 4.61 Å; (beryllium filter)
d= 0.889 Å - 1.54 Å
d= 1.39 Å - 2.44 Å
d= 2.66 Å - 4.61 Å
Flux at Sample: ~107 n.cm-2.sec-1 at thermal wavelengths
Detector : D19-type 2D-PSD, radius 730mm, 30o vertical x 120o horizontal. Efficiency >80% at 2Å
Resolution 2mm (0.15o) horizontal (charge centroid) x 2mm (0.15o) vertical (charge division)
120o oscillating radial collimator seeing d=5mm sample FWHM (Rint=120mm, Rext=300mm)
Design Features of the UK-CRG Diffractometer
An important reason why the flux on the sample can be higher with the continuous source is because the
resolution of a TOF diffractometer d/d depends essentially on the wavelength spread , whereas a
neutron monochromator can provide a  an order of magnitude greater than d/d because of
2
wavelength focussing. For example, the D2B monochromator reflects a  of about 1% even in the
high resolution mode where d/d is of the order of 0.1%.
Fig.1. The focusing of a wide band of wavelengths from a continuous source using a very large (300mm) composite
monochromator to increase the flux on the sample without sacrificing resolution (D2B and D20 high resolution geometry).
Na2Ca3Al2F14
Chi2 =
5.65
1.88 Å, 2 min
4
2.5x10 /2mn/0.1Þ
counting rate
2.0
1.5
1.0
0.5
0.0
10
20
4
30
40
50
60
70
80
2t heta
90
50
60
70
80
2theta
90
100
110
120
130
140
150Þ
Na2Ca3Al2F14
Chi2 =
4.06
1.37 Å, 2 min
1.2x10 /2mn/0.1Þ
counting rate
1.0
0.8
0.6
0.4
0.2
0.0
10
20
30
40
100
110
120
130
140
150Þ
Fig.2. Complex pattern obtained in only 2 minutes on D20 in high resolution mode. Different wavelengths are obtained, as on
D2B, simply by rotating the monochromator with the diffractometer fixed at a high take-off angle. (Hansen et al. 2003).
3
Clearly high resolution diffraction patterns can be obtained with very small samples when a large PSD
detector is used together with a large focussing monochromator at a high fixed take-off angle. The
combination of large detectors and high time-averaged flux on the sample will remain unique to the ILL
even when the new US and Japanese spallation sources are finally operational.
The new UK-CRG proposal will take these impressive results one step further by using an even large 2D
PSD detector of the kind developed for the EPSRC-D19 project.
Fig.3. The new 30ºx120º 2D PSD for D19. Large detectors match the solid angle of the best pulsed-neutron diffractometers,
while as well benefiting from the very high flux available on the sample at a reactor source. (Guerard et al. 2002).
The use of large 2D detectors is common for X-ray and synchrotron powder diffraction, but only recently
has been shown to work well for neutron powder diffraction, with the EPSRC-D2B project. With a large
2D detector, much more of the diffraction cones are collected. This intensity is integrated around the arc
of the cone, reducing the diffraction pattern to the classical Intensity vs Angle form. The simplicity of this
use of a large 2D detector on a reactor source is to be contrasted with the use of large detectors on pulsed
sources, where data of different resolution is spread over large numbers of pixels in the detector, and is
much more complicated to treat.
Fig.4. High resolution powder data from a large 2D detector, showing the curvature of the diffraction cones (Suard et al 2003).
4
High Pressure Environment of the UK-CRG Diffractometer
The new machine will provide D1A-like resolution with D20-like intensity, but in addition will use a
collimation system to make it especially suitable for the study of small samples in high-pressure cells and
other difficult sample environments. This will be a radial neutron collimator, as first pioneered on D1B
(see the ILL museum), later on machines such as DMC and HRPD at PSI and most recently on GEM at
ISIS. However the visible sample volume will be much smaller than that on these other machines, and
when used near 90o will eliminate scattering from almost all sample environments, and in particular high
pressure cells. Figure 5 shows the EuroCollimator (Cheltenham) design for the UK-CRG diffractometer.
Fig.5. The UK-CRG will use a radial collimator to cover a very large solid angle (120 o x 30o vertical) yet restrict scattering to a
very small volume of diameter ~5mm around the sample. (EuroCollimators Cheltenham, 2003).
A radial collimator consists of a stack of blades such that scattering is accepted at all angles from only a
small sample. The spatial transmission across the sample is a triangular function with FWHM
d=d1.(D+L)/L where:
d = diameter of visible sample
d1 = distance between blades at the front
D = distance to front of collimator
L = length of collimator
If we want to see only small samples d~5mm using a relatively large d1 (small number of short blades to
keep costs down) we need D as small as consistent with the space around the sample in its cryostatpressure cell eg D=120mm for L=180mm gives d=5mm for d1=3mm between blades, which would be
spaced at 3/120 radians or ~1.5 degrees.
5
Cost of the UK-CRG Diffractometer
Costs are at present indications only, since this proposal is so far only an “Expression of Interest”. It will
be relatively easy to arrive at precise costs, since the proposal only involves a novel combination of
techniques developed for other projects.
The UK-CRG diffractometer will use the super-mirror guide position vacated by D1A when the new
EPSRC strain scanner is completed further downstream. The much higher flux obtained with the new
guide, estimated at up to x5 by J. Saroun, will in any case require the re-construction of the D1A/D1B
casemat. The cost of the new casemat has then not been included in the present estimation.
The “old” D2B monochromator will be used for the UK-CRG. This is a modern composite-germanium
monochromator, 300mm high and vertically focussing. It was replaced on D2B only because the line
shape was not ideal for very high resolution, but it will be perfectly suited to the lower resolution of the
new machine.
The old D1A mechanical base will be re-used on a tanzboden floor – a similar base is used for D2B.
However some modernisation will be required, and of course the tanzboden floor must be constructed.
The detector is by far the main capital cost. This will be identical to that developed for D19, and we have
used the number estimated for that project, taking no account of the part due to development and
prototype testing, nor of the fact that a second blank detector box is already available. Generally it is
believed to be much cheaper to construct a second identical detector (eg Brookhaven quotations for the
D19 project).
The radial collimator is of great interest, but is in a sense an optional item; even D20 does not yet have a
radial collimator. The design and costing of the required radial collimator is well advanced with
EuroCollimators as can be seen from the detailed technical drawing above.
Finally, the cost of operating the machine is essentially the cost of detaching two postdoctoral scientists
and a half-time technician; it would obviously be a big advantage to the home laboratory to have a local
representative at ILL. The amount paid to ILL for services is small, and can be estimated from the
French-Spanish D1B-CRG, on the same casemat (~1.5K sterling).
Estimated costs in pounds sterling excluding VAT:
a) Capital Costs
1) D19-type 2D PSD detector & electronics (total estimated for D19)
2) New monochromator mechanics
3) D1A base modifications (new encoder, airpads etc)
4) Tanzboden floor
5) Radial oscillating collimator (optional)
6) Other costs
Total
b) Operational costs
1) Payments to ILL for services (cf D1B-CRG)
2) Annual budget for small items
3) Staff: detachment of two postdoctoral scientists plus 0.5 technician
700,000
7,500
22,500
25,000
60,000
10,000
825,000
1,500
5,000
Expression of Interest to be submitted to ILL by 10 October 2003 - see: http://www.ill.fr/Events/CRG/
6