Optically stimulated luminescence (OSL) dating laboratory
OSL dating can be used to determine the time since naturally occurring minerals, such as quartz and feldspar, were last exposed to light within the last few hundreds of thousands of years. It is one of the main methods used to establish the timing of key events in archaeology and human evolution, landscape and climate change, and palaeobiology in the latter half of the Quaternary. The age is obtained by measuring the radiation dose received by the sample since it was last bleached by sunlight, and dividing this estimate by the dose rate from environmental sources of ionising radiation.
The OSL dating laboratory is located in the School of Earth & Environmental Sciences and is headed by Bert Roberts and Zenobia Jacobs. It is recognised as one of the world’s leading archaeological dating laboratories, based on its track record of using OSL dating to answer internationally significant questions in archaeology and palaeoanthropology. Past and present research interests span a wide geographic compass, including Africa, Asia, Australia, Europe and North America, and topics as diverse as the evolution and behaviour of humans (Homo sapiens, Homo floresiensis and Homo neanderthalensis), their response to climatic changes over the past 200,000 years, and their interaction with the indigenous fauna and flora. The OSL dating laboratory is also at the forefront of technical advances in the analysis and interpretation of OSL data collected from single sand-sized grains of quartz, building on the pioneering research of Roberts and Jacobs in this field.
The new, state-of-the-art laboratory consists of separate rooms for the preparation and measurement of quartz and feldspar grains, as well as storage rooms for quarantined material. All rooms are fitted with safelights, similar to a photographic darkroom. A full range of modern facilities are available to extract and purify quartz and feldspar grains for dating. There are five Risø instruments to stimulate and detect the OSL emissions for purposes of dose determination, three of which have focussed laser attachments to permit measurements of individual grains of quartz and feldspar. The laboratory has two portable gamma-ray spectrometry units to measure the on-site dose rate from gamma radiation, and laboratory determinations of sample radioactivity can be made using a Risø GM-25-5 low-level beta-counting unit and three Daybreak 583 thick-source alpha counters.
PhD students and postdoctoral researchers are encouraged to become proficient in OSL sample preparation and measurement procedures, and in the analysis and interpretation of the resulting data. Some past members of the laboratory, such as Kira Westaway and Lee Arnold, now lead OSL dating laboratories elsewhere in Australia and overseas.
Two of the Risø instruments used for OSL dating in the UOW laboratory (top left). Grains of quartz or feldspar are mounted on stainless steel or aluminium discs and loaded into the instrument. Up to 48 discs can be measured in a single automated sequence. Grains are then optically stimulated by blue, green or infrared photons, and the OSL emissions are detected using a photomultiplier tube. For single-grain analysis, individual grains are deposited in holes drilled into custom-made discs and a focussed laser beam is shone into each hole (photos: Risø National Laboratory and Bert Roberts).
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