A few members
of the team that put together the X-ray CT lab with the X-ray equipment.
From left to right: Arthur Sakellariou, David Anderson, Tim Sawkins and
The X-ray CT Lab
the structures of materials with
X-rays and high-powered computers
Computer Tomography Laboratory probes the structure of materials by taking
a number of X-ray images of an object from a variety of angles. Computers
then stitch the images together to build a 3D model of the structure.
It's the same process as medical CAT (Computerised Axial Tomography)
scans used to image the body or the brain (although in medical applications
the patient stays in the same position and the X-ray scanner moves around
the body; in the CT lab the X-ray scanner stays stationary and the object
ANU's X-ray CT lab is an amazingly powerful and flexible facility that
is helping scientists unlock many of Nature's best kept secrets.
it: The X-ray CT lab is operated by the Department
of Applied Maths, part of the Research School of Physical Sciences
and Engineering. Applied Maths operates in the cross-disciplinary area
where chemistry, physics, biology, earth science and materials science
meet. It's involved in the fundamental studies of surface forces, liquid
crystals and mesostructured materials. The X-ray CT lab was constructed
as part of Applied Maths' continuing studies on the relationship between
structure and property.
it work: The key to understanding the structure and function of many
naturally occurring and synthetic materials is probing their structure
on many scales of length simultaneously, thereby relating microstructural
character with macroscopic performance. Further insight is gained if you
can observe the structures as they develop over time.
However making such measurements is extraordinarily difficult. While it
might be possible to take accurate measurements on one scale, say on a
micron scale, you normally have to use a separate machine and sample preparation
to take a measurement at a higher or lower scale. The restrictions are
magnified if you want to watch a sample develop over time.
The X-ray CT lab, however, is one of the few facilities in the world that
can measure over three scales of magnitude simultaneously - from microns
to millimetres. Further, the facility was purpose designed to be as flexible
as possible allowing a wide variety of samples to be analysed over a broad
range of time scales.
The apparatus is identical in concept to standard medical tomography,
with the exception that it is the sample which rotates within a fixed
X-ray microscope. The X-ray camera then records 2D radiographic information
over a variety of rotation angles. High-powered computer manipulations
of the data then allows the construction of a three dimensional image
of the sample's structure.
While X-ray tomography has been around for many years, the CT lab put
together by Applied Maths has many unique attributes which give it incredible
power and flexibility. The micro-focus X-ray source can produce a wide
range of X-rays (30-130 Kv) suitable for scanning soft biological materials
through to hard materials like stone .
The X-ray detector is an extremely sensitive 16-bit, scintillator-coupled
2048x2048 pixel CCD camera mounted on a linear rail allowing it be moved
back and forth from the sample and X-ray source. Moving the camera gives
a range of magnifications from 3x through to 100x. The sample is mounted
on a precision rotation stage, and the entire apparatus sits on custom-built
vibration isolators (allowing the sample, X-ray source and detector to
be rock steady over long time periods). The facility is contained in a
lead-lined room with safety interlocks.
Because the CCD camera is so sensitive, and the apparatus is so stable,
the X-ray source can be used at low power for extended periods of days
to weeks meaning structural changes can readily be monitored over time.
Because the apparatus is simple and open (ie, not encased in restrictive
lead shielding, the lead is in the surrounding walls) elaborate experimental
rigs can be accommodated.
On top of this, the CT lab has access to the awesome computing power of
the ANU Supercomputer Facility, though APAC, to allow rapid manipulation
of staggeringly large data sets. A single raw dataset may be as large
as 32 Gbyte.
Some of the research the CT lab will assist in includes the characterisation
and modelling of a wide range of materials including soils, sedimentary
rocks, minerals, wood, bone, polymer composites, foams, catalysts, coatings,
gels, concretes and ceramics. The results of this materials science will
include the development of improved biomaterials, achieving higher yields
of oil extraction from rocks, and designing better paper for printing.
The secret of its flexibility is its design. While most of the hardware
incorporated into the lab is off-the-shelf equipment, its the way it's
been configured together that gives it its power. And the credit for the
design and construction of the lab goes to a large team of scientists,
software designers, and electronics and mechanical engineers from all
over RSPhySE. Leading the way has been Stephen Hyde, Mark Knackstedt,
Tim Senden, Tim Sawkins, Arthur Sakellariou, Adrian Sheppard, Rob Sok,
Stuart Ramsden, Vanessa Robins and Christoph Arns.
More information: Dr Tim Senden