Optial Stimulated Luminescence Dating Laboratory

The OSL unit within the school is headed by Associate Professor Bert Roberts with team members Dr Hiro Yoshida and José Abrantes. The OSL lab commenced operations in 2001.

Like Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) is a method of dating quartz by allowing the electrons within the quartz crystal to escape in the form of photons (light). Rather than using heat to stimulate the quartz into releasing its electrons from their energy traps, OSL uses light as a source of stimulation.

In the time since the OSL unit commenced operations, there have been a number of different projects undertaken. One of the more interesting projects involved the dating of ancient mud wasp nests in order to establish an age for rock art in the East Arnhem Land area. Because the nests were built using material containing quartz, an age using OSL techniques was possible.   After obtaining several dates from the different nests this in turn allowed an estimate of when the rock art was created. For example, nests that were underlying the rock art were able to give a maximum age and nests that were overlaying the same rock art were giving a minimum age. Therefore we were able to narrow down an approximate age as to when the rock art was done, a kind of age band.

Other projects include several overseas ventures involving South East Asian archaeological sites in both Indonesia and Malaysia. Standard OSL technique is not appropriate in the area due to the high levels of feldspars and volcanic quartz, which display poor OSL emissions from the material in these areas. However, as a result of modern equipment, new methodology and sample preparation, reproducible ages of these areas are now possible.

The lab equipment consists of two OSL readers from Risø National Laboratories in Denmark. Of the two machines, one is capable of the fairly recent single grain technique. The most commonly used procedure is the single aliquot technique, which involves placing quartz grains ranging anywhere from several hundred to thousands of grains per disc placed equally over several discs. With the single grain method as many as one hundred quartz grains are individually placed on a disc which in turn are then analysed separately rather than a composite on the same disc, and several of these discs can also be done at the same time. The end result is a far more precise age can be determined due to the fact that each individual quartz grain is given its own date. Another advantage is that it can give further clues regarding how deposition took place or perhaps had the sediment been disturbed since deposition.

During the middle of 2004 the lab is expecting the delivery of its third OSL reader from Risø National Laboratories. With this new reader we will be able implement more new techniques as yet unavailable with our current readers. Methods such as Single grain analysis of feldspars through the use of Infra Red lasers and a more versatile Photo Multiplier tube which will have a broader light spectrum. Though the unit is a fairly new within the school we are committed to a future involving new avenues of research and the development of new protocols to advance the technique of luminescence dating.