MRI: Development of a Confocal Instrument for Spatially Resolved Luminescence Measurements in Geologic and Archaeological Dating and Radiation Dosimetry

East Carolina University, Greenville NC

Investigators

Abstract

Funds from this Major Research Instrumentation (MRI) Program grant will support development of a confocal instrument for spatially resolved optically stimulated luminescence (OSL) dating at Oklahoma State University. The instrument will support sedimentological/stratigraphic and archaeological research that relies on dating of natural and man made materials where no other geochronologic technique is possible (e.g., dating of Quaternary glacially rafted debris where no organics are available for radiocarbon dating, fluvial terrace gravels, beach boulders, mortars). Optically stimulated luminescence (OSL) dating allows for establishment of time of deposition (date of the last sunlight exposure of sediments) through the measurement of luminescence emitted from the sample during irradiation in the laboratory. Sunlight zeroes out luminescence by releasing the trapped electrons that accumulate at light sensitive crystal defects. The intensity of the emitted light (the OSL signal) is proportional to the radiation dose absorbed since burial, allowing calculation of time since deposition. Commercially available luminescence readers and techniques are limited to samples with individual mineral grains smaller than a few millimeters, preventing application of the method to bulk materials such as rocks, which excludes many geological and archaeological samples. The developed confocal OSL microscope will allow for fully automated, micron-scale spatial resolution of OSL dating over the depth of field. The instrument would expand the application breadth of OSL dating technique to solid samples larger than a few mm and therefore allow the technique to be applied to many previously undatable deposits such as those from gravel beaches, braided streams, and alluvial fans. The same dating technique may be used for determination of the construction or destruction date of archeologically significant buildings, which presently is only possible by dating the surrounding sediments. The instrument will also allow for spatially-resolved dose measurements that could provide information on microscopic variations in the environmental radiation dose rate and therefore improving the accuracy of the conventional OSL dating technique. The instrument will be the second confocal OSL instrument in the world and the first in the United States. Students at Oklahoma State will be afforded a unique opportunity to gain interdisciplinary experience in physics and engineering as well as geology and archaeology.