UNDERWATER BLEACHING OF SIGNALS FROM SEDIMENT GRAINS - NEW EXPERIMENTAL-DATA

The results of an underwater bleaching experiment are reported. The purpose of the experiment was to evaluate the degree to which thermoluminescence (TL) and optically stimulated luminescence (OSL) signals are reduced by a three hour exposure to light at different water depths. Samples of quartz and feldspar separates were annealed in the laboratory and then given fixed doses of laboratory beta radiation before exposure. The results indicate that a three hour light exposure is sufficient to zero the optical signals down to water depths of 10 m for feldspar infra-red stimulated luminescence and 12-14 m for quartz OSL. The TL results for the same quartz and feldspar samples exhibit some bleaching effects, with TL signals at 14 m water depth being reduced to 50-65% of the initial value. Scatter of the TL results limits their interpretation.