It is an essential tool for Victoria physicist, Andy Edgar and his group, who are developing scintillating and luminescent materials for X-ray imaging and detection, for applications in medicine, materials testing and security. About the Equipment: The new spectrometer fires a beam of ultraviolet light at a sample to excite the electrons and measures the luminescent light emitted. It has two important new functions. Firstly, it can measure luminescence in the infrared region of the spectrum whereas the previous spectrometer could only measure visible light. It measures light across a broad spectrum from 200 nanometres to 2.2 microns, with the excitation wavelength being selectable in the range 200-800 nanometres. Secondly, it can measure the luminescence ‘decay time’ – the time it takes for all the electrons to fall back to their ground state, which is a second characteristic property of the material. The spectrometer has a time resolution of less than 1 nanosecond. When coupled with an existing refrigerator facility, the new spectrometer permits luminescence measurements from room temperature down to twelve degrees above absolute zero, or -261˚C.
Andy’s group are developing materials for improved radiation imaging and detection, for example in medical imaging, including mammography, gamma-ray imaging for cancer detection, and PET scanning, an important technique for mapping brain and heart function and imaging tumours. They are also working on materials with applications in security, for example, in airports, and for materials testing, for detecting cracks in the structures of aircrafts or pipelines. For imaging, the luminescent materials replace traditional photographic film. They transform higher energy radiation such as X-rays into visible light that can be more easily recorded to create an image. The same conversion principle applies to scintillating materials, which are used in X-ray detectors. With the two extra functions on the new spectrometer, the group is able to take this research to a new level. The infrared capability is helping them to develop more sensitive materials which will give a clearer image in a shorter X-ray exposure time. Among other benefits this would mean lower doses of harmful X-rays to patients. The new spectrometer enables them to test these materials, which emit infrared light. The ability to measure decay times with nanosecond resolution is also a great advantage. A material with a short decay time can handle rapid changes in X-ray intensity, which means that, for example, PET scans can be done in a shorter time, an important consideration when the method uses radioactive isotopes with a life of just a few hours. “We work with materials that have decay times of tens of nanoseconds,” says Andy, “so we need to be able to do measurements on that time scale in order to compare the performance of different compositions”.
“This is a very flexible general purpose instrument with a wide range of operational capability”, says Andy. It is already being used by several research groups inside and outside the Institute. At Victoria University, nanoparticle expert Richard Tilley is using the new spectrometer to measure the luminescence of nano-particles. The facility is helping Raman spectroscopy expert Pablo Etchegoin, to develop methods of detecting single biological molecules in extremely low concentrations for applications such as early disease detection. Victoria chemist Gerald Smith is using it to analyse historic artefacts, both from local Maori culture and ancient civilisations overseas. The spectrometer is also used by other groups from Victoria and the Crown Research Institutes. “With the new spectrometer our published work will contain a more extensive characterisation of the materials we develop,” says Andy. “That will enable us to extend our position in the area of international competition.” He also expects the new facility to enhance his network of international collaborations, and the instrument has already resulted in a forthcoming visit from a colleague based in Germany.