Mark A. Rabin

The zeroing of the luminescence signal in quartz grains by exposure to natural light is a key principle in sediment dating using optically stimulated luminescence (OSL) dating. Determination of the "equivalent dose", De, which is the consequence of a residual luminescence signal not completely erased by light in the natural environment, is expected to yield values close to zero. However, zeroing of surficial sediments has rarely been systematically tested for a range of modern settings. OSL works by evicting trapped electrons in the crystal lattice of a quartz grain by green light stimulation in 0.5 second exposure intervals resulting in a luminescence signal. Different depositional environments should allow the sediments to be exposed to varying amounts of natural light, resulting in different OSL luminescence signals for each specific environment. The RAB-MB samples were taken from Martinique Beach, located on the Eastern Shore of Nova Scotia, and the HUD-2000-30A samples at depths of 29 m on the Scotian Shelf. Environments in question are lagoonal, beach dune, beach, and submarine sand dune. Using the single-aliquot regenerative-dose method De values of 2.053 " 0.308 Gy (natural irradiation) and 0.430 " 0.517 Gy (irradiated with 3 Gy of beta radiation) were acquired for RAB-MB-1, collected under shallow water in a back-barrier lagoon.. Due to time constraints, only one sample could be tested. The latter of the two De values suggests that with a suitable lab protocol, more accurate De values can be obtained. Although the standard deviation is high, the second De value satisfies an accurate zeroing of quartz grains in the lagoon environment.

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Pages: 63
Supervisor: D. Godfrey-Smith