Richard M. Bailey
Luminescence dating development
The general aim this work is to understand the behavior of electronic systems responsible for luminescence in natural crystalline materials, and to test and develop methods of dating. I use both theoretical and empirical methods and some of my ongoing research themes are described below.
Properties and behaviour of luminescence signals in natural materials
Most of this work has been focused on quartz luminescence and this has involved the development of a theoretical model. The aim was to produce a single kinetic model which could account for the known properties of quartz OSL and TL UV emissions. Model development involved laboratory experiments to both constrain model parameters and to assess the overall behaviour. This was a lengthy (and quite frustrating) process, but one which was ultimately successful. A flat band diagram representation of the model is shown to the right—the kinetic equations can be found in the papers listed below. This model has been used to investigate many aspects of quartz luminescence relevant to dating applications. One of these is the response to ionizing radiation (comparing natural and laboratory irradiation: natural rate being on the order 1e-14 Gy/s, whereas laboratory rates are typically ~1e-1 Gy/s). This work is continuing, with an empirical and theoretical investigation of dose response of quartz at relatively high doses (on the order of kGy).
The composition of the OSL signal and its properties have been another major focus of research. The quartz OSL signal was found to be a composite signal, with each component having specific properties. The dependence of the photoionisation cross section on stimulation wavelength is an example of such a difference and relevant data are shown to the right for the first two (’fast’ and ‘medium’ signals).
The dependence of the fast and medium OSL signals on wavelength provides an opportunity to improve signal deconvolution methods, by increasing the difference in optical depletion rates of the two signals during OSL measurement. An example of this is shown below the cross section data, where stimulation with 525 nm light produces considerable separation of the first two components. compared to the usual 470 nm stimulation. This phenomenon can be extended further by choosing a stimulation wavelength below the threshold response of the medium component, such that only the fast component is stimulated. Example data are also shown to the right, where quartz is stimulated at 160degC with 880 nm light. Some relevant references:
Bailey, R.M., Yukihara, E.G. and McKeever, S.W.S. Separation of quartz optically stimulated luminescence components using green (525 nm) stimulation (under review)
Bailey, R.M. Direct measurement of the fast component of quartz optically-stimulated luminescence and implications for the accuracy of optical dating (in press, Quaternary Geochronology).
Singarayer J.S. and Bailey R.M. (2004) Component-resolved bleaching spectra of quartz optically stimulated luminescence: preliminary results and implications for dating Radiation Measurements 38, 111 – 118.
Bailey R. M. (1998) Depletion of the quartz OSL signal using low photon energy stimulation Ancient TL, 16, 33-36.
Other recent research themes have included:
· Thermal dependence of signal growth rates (with specific focus on changes in electron trapping cross sections and the effect on palaeodose estimation)
· Single grain dating: simulation of single-grain OSL De distributions and selection of appropriate statistical treatments; thermal stability of single grain OSL signals
· Response of quartz OSL to beta-dose: simulation and measurement
· Refinement and simplification of quartz sample preparation procedures
· Long-range dating using thermally-transferred OSL signals
· The detection of incomplete pre-burial bleaching using OSL signal analysis