Sally sheds light on synchrotron imaging

Sally Irvine, Industrial Liaison Scientist - Imaging

Sally Irvine joined the Industrial Liaison team in October 2015 as an Industrial Liaison Scientist specialising in X-ray imaging. After completing her PhD with the School of Physics at Monash University in Australia in 2010, Sally spent over 3 years as a post-doctoral fellow working within the tomographic microscopy group (TOMCAT) at the Swiss Light Source. Following that role and prior to her position here at Diamond, Sally was a Research Officer for the Laboratory for Dynamic Imaging at Monash University.

With a background specialising in X-ray phase contrast and ultra-fast tomographic imaging, Sally has many years of experience gained from experiments conducted on synchrotron beamlines in Japan, Australia, the US, Switzerland and now the UK. This is well complemented by her research within live-imaging applications of high flux micro-focus laboratory sources.

Sally works closely with industrial users in order to assist them in taking full advantage of the diverse range of imaging capabilities on offer at a selection of Diamond’s beamlines. 

This is the most common imaging technique, and is the technique used in hospital X-ray imaging. An absorption contrast image is essentially a shadowgraph, the contrast being generated by the different attenuating power of materials in the sample. The small spot size and high intensity of synchrotron X-rays also make it possible to scan samples and provide a composite image in much finer detail than from conventional sources. Combining absorption contrast imaging with other X-rays techniques also allows detailed complementary information to be gathered, as in diffraction enhanced imaging, or to recreate three dimensional objects from two-dimensional scans as in tomography.

Phase contrast imaging takes advantage of the fact that different materials have different refractive indices. This produces a phase shift in the X-rays passing through the sample. By placing the imaging detector at a specific distance from the sample, interference between waves can be used to enhance contrast in the image.

It is particularly useful for enhancing the contrast of surfaces and interfaces in samples, which would not be visible using absorption contrast.

X-ray tomography is the construction of a three dimensional image from two dimensional projections taken at different orientations (usually with phase contrast or absorption contrast imaging). Tomography has many applications in the materials science, engineering and biomedical fields. It can be used to characterise the internal structure of porous materials such as trabecular bone or metal foams. Tomography can be used to determine the size and shape of cracks and other defects inside components such as aircraft parts, where unexpected failures could have catastrophic results. Because it is non-destructive, X-ray tomography can be used to study the internal structure of precious and unique objects in archaeology and palaeontology – for example studying ancient insects fossilised in amber.

Paleontology: Imaging fossilised plankton to understand prehistoric climate change E Read, AJ Bodey & S Redfern. 

Price, S. et al. DOI: 10.1002/anie.201504227

X-ray Fluorescence (XRF) occurs when the inner shell electrons of atoms in the sample get excited by the incident X-ray photons (synchrotron beam) and subsequently release X-ray photon when the system relaxes, that is when the electrons transition from the higher energy levels of the atom to the vacant inner shell. The beauty of this process is that each secondary X-ray photon (sometimes called characteristic radiation) emitted from the sample has a specific energy which is a fingerprint of the atom from which it has originated. By measuring the energy of the secondary photons it is possible to establish the elemental composition of the sample at the point where the X-ray beam hits the sample. Typically a special type of detector called energy-dispersive detector is used to precisely measure the energy of each photon. The plot of the number of photon counts versus their energy, the X-ray spectrum, typically shows a number of peaks which are directly associated with specific elements, so by just glancing at the spectrum it is possible to quickly deduce which elements are present in the sample.

Coherent X-ray diffraction is an imaging technique which overcomes some of the limitations encountered with using lenses. Instead, a series of X-ray diffraction patterns are combined to mathematically reconstruct a three dimensional image of the structure being studied. With highly coherent synchrotron X-rays, this approach can provide spatial resolution on a nm scale. In the past this technique has been applied to model repeating crystal structures, but it is now being used to examine small, non-periodic samples.

The technique is in the very early stages of development and available only to experts through the peer review access route at this stage,

PhotoEmission Electron Microscopy (PEEM) is a non-destructive imaging technique that involves shining linearly or circularly polarised X-rays onto the surface of a sample to provide spectroscopic information on a nm scale. This information can be used to study nanostructures significant for sensors, catalysts, magnetic materials and nanoscale devices and phenomena such as nanomagnetism.