Research projects: Aberystwyth Luminescence Research Laboratory


	Aberystwyth Luminescence Research Laboratory

	Research projects in Aberystwyth
EFCHED research	Luminescence research in Aberystwyth follows four main themes. These are:- Development of equipment for luminescence measurements Improving our understanding of the luminescence properties of natural minerals Development of measurement procedures for evaluation of dose using luminescence Application of luminescence dating to key chronological issues in the Quaternary
Above: Single grain laser stimulation system mounted on a Risø automated TL/OSL reader. The measurement chamber, where the sample is placed, is in the upper-right of the picture. In normal operation the entire system is covered in order to make it light-tight.	Development of equipment for luminesence measurements The most significant development in the last five years has been the single grain OSL system developed in collaboration with Risø National Laboratory. As can be seen in the image on the left, this system consists of a green (532 nm) laser which can be steered to any position within the measurement chamber. The beam can then be directed to stimulate the luminescence from any one of a hundred grains mounted on a special 9.7 mm diameter aluminium holder (see below). Typically grains between 180 and 210 micrometers in diameter are used. The ability to measure individual grains is vital when dealing with complex sediments where it is not possible to assume that all grains were exposed to sufficient daylight at the time of deposition for the luminescence signal to be completely reset. Such complex mixtures of grains, some of which have had their luminescence signal reset and other which have not, may exist in a range of depositional settings. We have undertaken research into glacial and fluvially deposited sediments. In addition, in archaeological sites, especially cave sites, there may be a possibility that sediment mixtures occur. Above: A sample holder for single grain measurements. The aluminium disc is 9.7 mm in diameter. A grain of quartz is in each of the 100 holes. Further reading: Bøtter-Jensen, L., Andersen, C.E., Duller, G.A.T., Murray, A.S. (2003) Developments in radiation, stimulation and observation facilities in luminescence measurements. Radiation Measurements 37, 535-541. Duller, G.A.T., Murray, A.S. (2000) Luminescence dating of sediments using individual mineral grains. Geologos 5, 88-106. Duller, G.A.T. (2003) Distinguishing quartz and feldspar in single grain luminescence measurements. Radiation Measurements 37, 161-165. Duller, G.A.T., Bøtter-Jensen, L., Murray, A.S. (2003) Combining infrared- and green-laser stimulation sources in single-grain luminescence measurements of feldspar and quartz. Radiation Measurements 37, 543-550. Duller, G.A.T. (2004) Luminescence dating of Quaternary sediments: recent developments. Journal of Quaternary Science 19, 183-192.
	Improving our understanding of the luminesence properties of natural minerals Understanding the luminescence response of natural minerals to ionizing radiation is fundamental to the succesful application of luminescence to Quaternary dating. The two minerals most intensively studied for luminescence dating are quartz and feldspar. Research by staff in Aberystwyth has taken both a physical and a phenomenological approach to such studies. Key advances have been in the development of knowledge regarding the impact of thermal treatment on quartz and feldspar. Further reading: Duller, G.A.T. (1997) Behavioural studies of stimulated luminescence from feldspars. Radiation Measurements 27, 663-694. Duller, G.A.T., Botter-Jensen, L. (1997) Optically stimulated luminescence emission spectra from feldspars as a function of sample temperature. Radiation Measurements 27, 145-151. Roberts, H.M., Wintle, A.G. (2003) Luminescence sensitivity changes of polymineral fine grains during IRSL and [post-IR] OSL measurements. Radiation Measurements 37, 661-671. Wintle, A.G., Murray, A.S. (1997) The relationship between quartz thermoluminescence, photo-transferred thermoluminescence and optically stimulated luminescence. Radiation Measurements 27, 611-624. Wintle, A.G., Murray, A.S. (1999) Luminescence sensitivity changes in quartz. Radiation Measurements 30, 107-118. Wintle, A.G., Murray, A.S. (2000) Quartz OSL: Effects of thermal treatment and their relevance to laboratory dating procedures. Radiation Measurements 32, 387-400.
	Development of measurement procedures for evaluation of dose using luminescence The Research at Aberystwyth has been crucial in improving the methods that are available within luminescence for determining the radiation dose, measured in the SI unit of the Gray (Gy), to which as sample has been exposed during burial. This quantity, known as the palaeodose (P) or equivalent dose (ED or D_e) is one half of the basic age equation used in all luminescence dating. Age (ka) = Equivalent Dose (Gy) Dose Rate (Gy/ka) Work by Duller (1991, 1995) pioneered a suite of techniques in which all the measurements necessary to calculate an equivalent dose could be undertaken on a single sub-sample (or aliquot). This was a major advance over existing mutliple aliquot techniques which required between 20 and 50 aliquots to determine a single equivalent dose. The single aliquot additive dose method developed in Aberystwyth was adopted widely during the 1990s. In the last five years another single aliquot technique, this time suitable for use with quartz, has been developed jointly by Prof Ann Wintle and Dr Andrew Murray (Aarhus University). The single aliquot regenerative dose (SAR) technique (Murray and Wintle 2000, 2003) utilises the fundamental studies of the behaviour of quartz to correct for changes in lumienscence sensitivity during the procedure. The SAR procedure has now been adopted by the majority of luminescence research laboratories in the world. More recently, Roberts and Duller (2004) have investigated the existence of common patterns in the form of the SAR growth curve between samples from different geographical regions. This approach simplifies the determination of equivalent dose, reducing the number of luminescence measurements that are required. Further reading: Duller, G.A.T. (1991) Equivalent dose determination using single aliquots. Nuclear Tracks and Radiation Measurements 18, 371-378. Duller, G.A.T. (1995) Luminescence dating using single aliquots: methods and applications. Radiation Measurements 24, 217-226. Murray, A.S., Wintle, A.G. (2000) Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57-73. Murray, A.S., Wintle, A.G. (2003) The single aliquot regenerative dose protocol: potential for improvements in reliability. Radiation Measurements 37, 377-381. Roberts, H.M., Duller, G.A.T. (2004) Standardised growth curves for optical dating of sediment using multiple-grain aliquots. Radiation Measurements 38, 241-252.
	Application of luminescence dating to key chronological issues in the Quaternary The evolution of Holocene dunes in Michigan Chronology of Middle Stone Age (MSA) sites in Africa Rates of loess accumulation in the mid-west United States of America Rates of linear dune migration,Namibia History of sand deposition on Anglesey Timing of archaeological events Past projects:- Providing a time scale for pedogenic magnetite formation in China Determining periods of colluviation recorded in hill slope deposits in South Africa History of coastal sand dunes in Northumberland and North Norfolk Coastal dunes in Ireland Earthquake chronology in southern Israel Loess accumulation in the northwest USA The Late Quaternary in the Mojave Desert, California Key Quaternary sites around the margins of former Scottish ice sheets
	If you have any queries about any of these research projects then please contact Prof Geoff Duller (ggd@aber.ac.uk), Dr Helen Roberts (hmr@aber.ac.uk) or Prof Ann Wintle (aqw@aber.ac.uk).
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