REQUEST FOR PERKIN ELMER XRD0822 FLAT PANEL X-RAY DETECTOR FOR THE COMPUTED TOMOGRAPHY (X-RAY CT) INSTRUMENT IN GEOSCIENCES

Transcription

1 REQUEST FOR PERKIN ELMER XRD0822 FLAT PANEL X-RAY DETECTOR FOR THE COMPUTED TOMOGRAPHY (X-RAY CT) INSTRUMENT IN GEOSCIENCES STATUS: This bid was submitted to the sustainability pot in 2010 and received support by the EPS group and the School for funding. It was ranked as worthy of support, but being just below the final cut off, it was marked to be carried over to the 2011 round. To that end we resubmit the bid to the EPS and School with updated costs. Proposers Ian Butler, Stephen Elphick Supporters U0E;-Geosciences Geoffrey Bromiley, Mark Chapman,,Simon Harley, Stuart Haszeldine, Ian Main,Christopher McDermott, Bryne Ngwenya, Thor Thordarson, Rachel Wood, U0E;-CSEC Konstantin Kamenev, U0E;-Engineering Chris Hall, Jane Blackford HW;- Gary Couples, Rink van Dijke, Sebastian Geiger, Ken Sorbie. SUMMARY We request support to buy a PerkinElmer XRD0822 X-ray detector for the X- ray Computed Tomography (X-ray CT) instrument recently constructed in-house under the ECOSSE program. The new detector will allow imaging and 3D reconstruction of large dense samples such as carbonate cores and dense caprocks for ICCR and carbon sequestration research, related experimental fluid flow, CO 2 and deformation studies, and allow imaging of experimental and technical samples containing dense inclusions or parts. The detector and related components will cost 47,690 including 20% VAT CONTEXT The advantage of having a dedicated X-ray Computed Tomography instrument available on-campus has been appreciated for the last decade. Prof. Chris Hall submitted a full EPSRC proposal for 345,187 in 2005, which was unfortunately not funded. The difficulty has been that because CT is an enabling technology, and might form only part of a research proposal, demonstrating an active user need is impossible without easy prior access to a suitable instrument, while writing full CTbased proposals needs initial guaranteed instrument access time. Thus demonstrating to a funding council ex novo the need for an expensive full-scale commercial installation is almost impossible. Availability of ECOSSE funding, and willingness to purchase only core components and undertake integration and development in-house, has allowed us to sidestep the funding problem. We have constructed an unenclosed X-ray Computed Tomography instrument in a part of the experimental laboratories where blast-proof walls provide the required radiation shielding, and where there is potential linkage to existing experimental capability. Essentially similar to a hospital CT scanner in providing reconstructed 3D volume images of samples, the new instrument is modular system on a granite optical table, providing maximum flexibility for geological and engineering samples. By specifying in-house, purchasing the essential components individually, and assembling the instrument and drive software ourselves, we have gained access to functionality at a cost of some 30% of the price we know companies have paid for similar research capability.

2 TECHNICAL SUBMISSION What is a CT instrument A functional CT unit consists of five critical elements, three mechanical, and two software. The mechanical components are an x-ray source, a rotating table holding the sample, and an X-ray camera or planar detector. Added to this mechanical unit is the software package which interlinks the rotating table to X-ray image capture and download software, and the software packages for 3D reconstruction and 3D image manipulation. Medical CT is in essence the same, but the X-ray source and camera are rotated, because you are not allowed to spin the patient. Figure 1: The ECOSSE CT instrument (left) and a generalised instrument configuration for cone beam CT data collection (right) To obtain a 3D volume image of a sample, the sample is rotated once by the table on which it is mounted, while a set of X-ray images are taken at regular angular intervals. From this X-ray image set a reconstruction software package can generate a digitised 3D model of the object, and this volume image can be sliced or density selected as required. The quality of the images generated is determined by the spot size of the X-ray source, and the sensor or pixel spacing in the X-ray camera. The amount of magnification is determined by how close the sample is placed to the source relative to the distance between source and camera. For example, a small sample can be heavily magnified by placing it close to the X-ray source, so that it casts a large X-ray shadow onto the camera. How does our current capability compare Our in-house CT instrument is equal in capability to any but the most specialist NanoCT instruments, and equals or betters current commercial instruments. The component list is very similar to that specified by the University of Ghent when setting up their CT laboratory, because the individual components are the best that either group could source. Figures appended illustrate that on small samples such as individual oceanic forams we can achieve a voxel resolution of one micron. (A voxel is the volumetric equivalent of a pixel in 2D) This means that we can map the internal volume and geometry of a 1mm foram at 1 micron resolution. We can

3 achieve this resolution because the X-ray source can achieve sub-micron spot sizes, and the X-ray camera has a pixel pitch of 50 microns, one of the finest available. By varying the position of the sample between X-ray source and camera, we can image suitable samples between 1mm size at one micron resolution up to 50mm samples at 50 micron resolution. The capability of our current instrument is shown in Figs 2-5 appended. Technical justification for new camera The Problem When specifying the initial CT mechanical component set, of X-ray source, revolving sample table, and X-ray camera, we had to purchase a matched set suitable for as wide a range of potential ECOSSE and School samples as possible, within the constraints of available funding. After rigorous specification, we purchased a CMOS camera with 10cm by 10cm active area. This camera has: 1) a 50 micron pixel spacing, giving access to high resolution (4 megapixel) capability for small samples, 2) is a good match to the available energy range from the X-ray source, and 3), a reasonable (12-bit) range in its exposure capability. The latter is important because it is capture of subtle ranges of density variation which enable detailed 3D reconstructions. It is notable that University of Ghent began their CT unit with a similar camera from the same manufacturer, presumably for the same reasons. Although this camera gives superb images and reconstructions, as instanced by the images appended to this request, it necessarily also has some compromise features. These are; the limited size of the camera capture area, the sensitivity range available per image, and the susceptibility to radiation damage. The 10cm by 10cm active area of the current camera means that this is the largest sample which can currently be imaged. The situation is slightly worse, however, because the width of the sample table makes it mechanically impossible to place the sample immediately adjacent to the camera. There is thus always some geometric magnification during imaging, meaning that the largest sensibly achievable sample size is currently 5 cm width by 7cm tall. The 12-bit image greyscale depth of the present camera is very reasonable, but for certain types of sample, such as larger carbonate or caprock core samples, so much energy is absorbed by the sample that the image which can be captured is lacking in exposure detail. In other words, all the image detail needed to enable a 3D reconstruction is contained within a band of 3 or 4 bit depths within the 12-bit greyscale nominally available from the camera. The only way around this problem is to take multiple images at each individual position, and rescale these to a single image frame with better resolution. However, a detailed reconstruction of an average sample usually requires a 10 second exposure step at 800 different positions, taking 1hour 20 minutes for data capture alone. Multiplying this by five to achieve adequate image tonality becomes very burdensome. Our CT is not unusual in this, detailed core scanning to the resolution we can reach is routinely reported as taking 24 hours. Lastly, there is the problem of radiation damage, which is linked to the first two aspects above. The X-ray camera consists of a scintillator deposited over an optoelectrical sensor array. When an X-ray hits the scintillator, it generates a flash of light which is captured by the underlying electronics. While this digital geometry is powerful, and has replaced X-ray film in medical imaging work, it necessitates the electronics being placed directly in the X-ray beam. This results in gradual

4 degradation of the imaging capacity of the camera, ie it is slowly fried by the X-ray beam, and gives a gradually poorer and grainier image. Unfortunately, CMOS cameras are particularly susceptible to this radiation damage, which limits their use to specialist imaging applications. The three individual weaknesses of the current CMOS camera are selfreinforcing for an important subset of samples of great geological interest for oil and sequestration studies. Worst case is detailed imaging of 38mm dense carbonate core. In this application, the sample is so attenuating that both the X-ray energy and power have to be maximised to obtain a reasonable image in a sensible time. However, X- rays hitting the camera around the edges of the sample, where there is no heavy attenuation, are blasting directly at full power into the camera electronics. This, and the required prolonged exposure times to achieve decent images, causes excessive cumulative radiation damage down the edges of the current CMOS camera. The solution The practical solution adopted by research CT facilities is to use different cameras dependent on the sample type involved. We propose purchasing a Perkin Elmer XRD0822 for use with dense and large samples. This camera has an image area 20cm by 20cm, four times that of the present camera, allowing us to image much larger samples. The proposed camera can capture 100 frames per second, against the 2.7 frames per second of the current CMOS camera. This makes it is better suited to the capture of transient phenomena such as labelled fluid flow in samples. And most importantly, the Perkin Elmer camera uses an amorphous silicon detector type which is much less sensitive to radiation damage than our CMOS camera, and is available in a range of scintillator types that can be matched to the high energy range of our system. These cameras are used in routine Non-destructive Testing (NDT) environments, under continual X-ray irradiation, and are very heavily shielded. The proposed camera would add critically to our capability in an important area of imaging and CT work. COSTINGS Detector Type Short description Price in EURO XRD 0822 CP3 IND fps, Rad Hard Panel 36, Accessories Power Supply XRD-EPS 215W H 1, XRD EPS B2 DC Cable 7.6m H XRD EP Power Supply AC Cable EP DE H XRD GigE Interface Cable 50Ft / 15.25M H Shielding Cassette 160kV (Optional) H 1, Prices are Ex-Works Wiesbaden (Germany) TOTAL EX VAT 39, TOTAL INC VAT@20% 47,690.00

5 BUSINESS AND SCIENCE PLAN Current Profile Component specification, sourcing, purchase and integration has taken two years, with the X-ray source commissioned Aug The first tomographic 3D reconstruction was obtained in Jan Because we have been learning as we go, including optimising drive and data software, and learning the essential parameters for obtaining research-grade 3D images, we have not advertised the CT capability, but allowed the science project base to grow organically through the ECOSSE collaborative mechanism. In some projects CT gives added value, in others, it is a critical component of the research proposal. All access except proof of concept for grant proposals is at FEC rating. Projects in progress or funding secured IMVUL towards improved aquifer vulnerability assessment EU Framework 7 Marie Curie ITN. 48 Months. Dr S. Elphick, Dr B Ngwenya and Dr I Butler. 405K ( 3.2M total network budget). CT imaging of biofilm growth CO 2 SolStock - Biobased Geological CO 2 Storage. EU Framework 7 Future Emerging Technologies Round. 36 Months. Dr B. Ngwenya Dr I. Butler, Dr S. Elphick, Dr R. Wood, Prof S. Haszeldine. 2.98M Coordinated by Edinburgh. 817K to Edinburgh. CT imaging of biological precipitates in sand and soils MUSTANG - A Multiple Space and Time Scale Approach for the quantification of deep saline formations for CO 2 storage 24 Months. Dr C. McDermott, Prof. S Haszeldine and Dr I Butler. 9.8M Total project, 610K to Edinburgh. CT imaging of CO2-water-rock reaction zone in cap rocks (essential project component) Validation and verification of discrete fracture flow models for fractured carbonate rocks EPSRC/Exxon-Mobil Case Studentship. 36 months. Dr S. Geiger (HW), Dr I. Butler, Dr S. Elphick 87K (ECOSSE Project held at HWU). CT imaging of fluid flow in fractured carbonates (essential CT component) Localizing signatures of catastrophic failure (LOCAT) EPSRC/ERC Project Grant, and part of European Complexity Network. 24 Months. Prof. I. Main, Dr I Butler, Prof M. Zaiser (Engin.). 127K CT Characterisation of fractured materials Satutrack - Saturation tracking and identification of residual oil distributions using X-Ray CT, SEM, and pore-scale modelling techniques. Petrobras industry funded project supported through ICCR. 36 Months. Dr I. Butler, Dr S. Elphick (UoE), Dr S. Geiger, Dr R. van Dijk, Prof K. Sorbie (HWU). 183K CT measurements of oil/brine distributions in porous carbonates (essential CT component) In-situ X-ray tomographic imaging under extreme conditions: a proof of concept study. NERC Small Project Grant. 18 months. Dr G. Bromiley, Dr I Butler. 57K CT method development for on-line HPHT experimentation.

6 Current User Base UoE Geoscience Users through project association: I. Butler, G. Bromiley, S. Elphick, S. Haszeldine, I. Main, C. McDermott, B. Ngwenya,, R. Wood,. Other UoE users (through project association or applications) Prof. M. Zaiser, Dr Jane Blackford. Project Students, PhDs, Postdocs and Resarch Techs: Ms M. Berg (PhD), Ms. H. Kurlanda (Marie Curie PhD), Ms C. Fricke (EPSRC PhD HWU), Dr K. Edlmann (EU PDRA), Mr K. Dodds (EU Research Tech) Mrs Tannaz Pak (ICCR PhD). ECOSSE Users (Through Project association) Dr S. Geiger, Dr R. van Dijk, Prof. K. Sorbie. (all HWU) Wider Interest from other institutions and industry: Dr Richard Harrison and Dr Nathan Church (Cambridge Earth Sciences); Dr Stig Walsh (National Museum of Scotland). Collaboration with Exxon-Mobil and Petrobras (through links to HWU and through ICCR). Future Profile Now that there are established users, and confidence in the stability of the component and software interoperability, it is feasible to start longer-term planning for the CT instrument. The first step is to upgrade the camera, to optimise imaging capability, which the current application addresses. The current manual component positioning system is being upgraded to precision motor-driven placement, making the instrument much more user-friendly. The instrument and its capability will be more widely advertised through the School and via the ECOSSE mechanism, enabling researchers to plan CTbased projects which will have competitive novelty compared with other institutions. As usage builds up, and can no longer be serviced by existing in-house staff, the full FEC costings we use will allow training of an operator/software engineer, first on a part-time basis, and then full-time. The dedicated in-house expertise can then be leveraged across the Science faculty to help develop novel CT applications and techniques, a model which has proven successful at the University of Ghent, where a small CT capability has been built into a thriving science and software unit. Our aims are more modest, to provide a center of excellence for CT related imaging and experimental work in Scotland, with the potential for additional growth if it proves merited.

7 Figure 1: X-ray CT image of a fractured carbonate core (lower image) with the fracture volume extracted and rendered separately (upper image). Figure 2: X-ray CT image of a woodcock skull. Data acquired in collaboration with Dr Stig Walsh, National Museum of Scotland.

8 Figure 3: X-ray CT reconstruction of an olivine-fe/fes pellet from high pressure and temperature piston cylinder experiment. In images a-d 3D rendering software has been used to increase the transparency of the olivine matrix (green) to reveal the distribution of Fe/FeS inclusions within the sample. Sample diameter = 2mm, scan resolution = 3 microns.

9 Figure 4: X-ray CT reconstruction of a single foraminifera showing details of internal structure of the carbonate shell (Sample diameter = 1mm, scan resolution = 1 microns).