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Aug 19, 2011

Corporation launches microfocus X-ray machine

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Anew microfocus X-ray radiography and tomography machine, for use by South African scientists and researchers, has been launched by the South African Nuclear Energy Corporation (Necsa) at its Pelindaba complex, near Hartbeespoort, in the North West.

South African National Centre for Radio- graphy and Tomography (Sancrat) and Necsa chief scientist for neutron radiography/ tomography Frikkie de Beer explains that use of the facility has been reserved for postgraduate researchers until the end of the year, after which it will be available for use by other researchers.

The device is a self-contained, 225 kV microfocus X-ray computed tomography machine that has a five-axis sample mani- pulator and can be used to study samples up to about 300 mm in diameter, says Belgium-based metrology and radiation imaging specialist Nikon Metrology X-ray imaging engineer Carsten Rudolf.

The machine uses an electron beam focused, in a micrometre-range-sized spot, onto an X-ray-producing multimetal target, either tungsten, copper, molybdenum or silver, which enables researchers to produce different spectra of X-rays without breaking the vacuum chamber.

It boasts chilled-water cooling of the electron beam tube and the X-ray-producing target rod to ensure a stable temperature environment, which improves the consistency and repeatability of results between multiple tests and samples, he adds.

The conical X-ray beam is centred on a Perkin-Elmar flat panel detector about 1 m away from the X-ray source and uses geometric magnification, because X-rays are not modified by lenses, that sees the sample moved closer or further away from the X-ray focal point to produce magnification effects of the signals captured by the detector.

The captured signals are then fed to the heart of the system – a series of computers that use dedicated software to reconstruct the images taken into a three-dimensional (3D) representation of the sample (virtual image), enabling researchers to study and obtain quantitative information (such as volume and size distribution) of the varied materials and surfaces of the samples in a noninvasive and nondestructive manner.

The machine can penetrate, for example, aluminium samples up to 100 mm thick. However, for denser materials, such as carbonates in rocks, steels, titanium or uranium, the samples must be reduced in size and thickness to enable the X-ray beam to penetrate.

Further, the machine can also be fitted with a rotating reflection target. This means that the electron beam focal spot on the target moves in a circle as the target is rotated, enabling a higher energy electron beam (increasing its flux) without melting the surface of the target.

Generating X-rays is an inefficient process where a lot of heat is produced when generat- ing only a few X-ray photons. However, with better cooling, power on a rotating reflection target can be increased over a smaller focal spot or the flux increased to enable faster throughput, says Rudolf.

“Using the same electron beam, the machine can be set up to produce small focal spot sizes, such as spot sizes between 3 µm and 5 µm for reflection targets, 10 µm on rotating targets and 1 µm on transmission targets, which enables researchers to detect inclusions, voids or material properties in resolution of about the spot size if one moves the object close to the focal spot,” he adds, highlighting the machine’s versatility to serve the South African research community.

Objects larger than 300 mm in diameter can be placed in the machine and a partial image generated, but only if X-rays can penetrate the sample and if it fits into the machine. Multiple images of an object can then be combined to create one image of an object larger than 300 mm in diameter using Nikon Metrology’s software, he notes.

The machine and its software have also been designed to enable users to see the contrast between similar-density materials, such as carbon fibres present in a carbon-composite material. Both the fibres and the material are chemically carbon but, by varying the spectrum of the X-rays, the attenuation of the materials can be detected, enabling the machine to produce images from similar- density samples, notes Rudolf.

Indeed, global diamond giant De Beers’ technology division DebTech principal scientist Dr Cecil Churms, speaking at the launch of the system in July, said he had used similar microfocus X-ray technology to identify diamonds present in a core sample by using both the high-power end of the machine’s capabilities, as well as its low-power capabilities, and then used his own mathematical expertise, knowledge of geology and the system’s calculating software to combine the data sets into a 3D model that represented the positions of the diamonds in the sample.

He told the mathematically inclined members of the audience that he used a Fourier transform to Fourier space, weighted it according to the frequency and then did an inverse transform.

Churms emphasised that, by understanding the machine and understanding how variations in parameters affect the image acquired, researchers can get excellent results, even if presented by technically challenging samples, such as a diamond- bearing core sample.

South African and International Research

This system forms part of Necsa’s National Beam Line Centre, which promotes and manages the use of different forms of electro- magnetic and neutron radiation imaging to conduct tests and research.

The centre will comprise the newly launched microfocus X-ray radiography/ tomography facility (Mixrad) and the South African neutron radiography/tomography facility (Sanrad), as well as two more facilities that are being built, namely the high-energy X-ray radiography/ tomo- graphy facility and the gamma radiation radiography/tomography facility, says De Beer.

All the facilities will be operational by 2015. However, the Sanrad facility will be taken off-line in 2012 for one-and-a-half years to enable upgrades that will make it compliant with European standards and operation capabilities.

“The microfocus X-ray addition intro- duces a new era in research with X-ray imaging for South African scientists because the instrument provides a research platform from which competitive applications for beam time at advanced synchrotron facili- ties abroad can be made. Although a few microfocus X-ray instruments are in operation in South Africa, beam time will be available free for general research.

“The Sancrat team works in collaboration with visiting scientists and researchers to Necsa and advises them on the use of neutron or X-ray imaging during their research. We help researchers and clients to obtain the best 3D tomographs from the imaging systems and assist in the evaluation and analysis of the data they have obtained from the machine.”

Further, research scientists and industrial scientists can apply online for beam line time at Sancrat’s facilities during next year, and specifically for Mixrad beam line time from October this year. Information about Necsa’s radiation imaging capabilities is also provided online for researchers to consider.

“The Mixrad facility can be applied to many fields of science, including palaeosciences, archaeology, geosciences, energy (nuclear and coal), biosciences (anatomy and food sciences), civil, mechanical and chemical engineering, as well as nondestructive testing,” he says.

Necsa’s mandate, as determined under the Nuclear Energy Act, is to perform and support research and development in the field of nuclear and radiation science and technology. For Necsa, it is important that this knowledge does not stay at Pelindaba but is used in a collaborative fashion with South African institutions, as well as international institutions, he says.

“We see ourselves as part of the South African national system of innovation and, with our capabilities and our work, aim to ensure that science and technology make a growing difference to our socioeconomic situation and, importantly, to skills development. It places South African capabilities in this regard on par with international standards. We believe this will lead to the development of high-level expertise in South Africa and we hope that we will grow within our role and participation in this.”

Industrial applications of research and development are a crucial part of Necsa’s mandate and partial funding for the machine from the National Research Foundation reflects the view that science and research can help to change South Africa’s socio- economic situation, he concludes.

Edited by: Chanel de Bruyn
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