Imaging Luminescence Using Focussed Stimulation: A Potential Solution to Problems of Heterogeneity in Dating Sedimentary Systems

Houston, Iain James (2001) Imaging Luminescence Using Focussed Stimulation: A Potential Solution to Problems of Heterogeneity in Dating Sedimentary Systems. MSc(R) thesis, University of Glasgow.

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Abstract

In this thesis the potential of using scanning instrumentation coupled to focussed lasers to measure luminescence from single grains was explored. An original concept was used to build an instrument capable of conducting single grain measurements. The thesis focusses on the evaluation of this instrument through experiments using FI feldspar which were subsequently reinforced by numerical modelling. Development of the scanning instrument was initially prompted through measurements on samples from the NE Thailand "cover sands" for which competing aeolian and bioturbation origins have been proposed. In the case of aeolian deposition the doses found within the grains should be relatively homogeneous. If mixing has occurred within the layer then there is likely to be a large grain to grain variation in stored dose at some depths. In problems of this nature single grain luminescence analysis should be capable of identifying which of these models is more appropriate. Initial experiments produced images of FI feldspar grains on conventional discs revealing that the IR laser, which was widely used for the single grain measurements, operated with a visible spot size of around 100 mum. This spot size was small enough to produce meaningful images and individual grains could be imaged if they were separated widely enough. A single scan was found to remove the bulk of the measurable signal from the grains. It was also shown that the system had the potential to measure doses as small as 2 Grays. Further investigations were conducted on the effect of scattered light within the sample chamber. Numerical modelling showed this effect should result in an initial peak in the results as well as a gradient throughout the measurement. This effect was observed in some results. Numerical modelling also showed that on more sparsely covered discs the effect of laser scatter would not be as marked. Attempts were made, using several different approaches, to reduce the effect of this scatter when measuring evenly covered discs. Although it was not possible to reduce the effect of such scatter it was found that presenting the grains in pits within the discs appeared to eliminate the problem. Finally, measurements on evenly covered discs of irradiated and unirradiated feldspar blends of known concentration tested the potential of the system for measuring samples of mixed grains with different luminescence characteristics. The results produced by these analyses were found to be consistent with those produced by numerical modelling. To conclude, results using FI feldspar suggest that the performance of the system is sufficient to determine whether mixing has occurred. Improvements are suggested which would further refine the instrument to allow the detection of mixing in samples from natural environments.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: Tony Fallick
Keywords: Geochemistry, Analytical chemistry
Date of Award: 2001
Depositing User: Enlighten Team
Unique ID: glathesis:2001-74956
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 15:00
Last Modified: 27 Sep 2019 15:00
URI: http://theses.gla.ac.uk/id/eprint/74956

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