Dating Sediments by EPR Using Al-h Centre: A Comparison between the Properties of Fine (4-11 mu m) and Coarse (>63 mu m) Quartz Grains

The possibility of EPR dating for sediments using Al-h signals of fine (4-11 mu m) grains of quartz has not been previously discussed. Here, the Al-h and peroxy EPR spectra of fine (4-11 mu m) and coarse (63-90, 125-180 mu m) sedimentary quartz from thoroughly investigated loess sites in Eastern Europe were examined. By comparing experimental spectra with a simulated signal, we evaluated the overestimation observed when using the standard approach established by Toyoda and Falgueres to measure Al-h intensity for different doses of radiation, up to 40,000 Gy. This overestimation, caused by the presence of peroxy signals, was much more pronounced for fine grains. Fine grains exhibited some additional dose-dependent signals, which, for some samples, caused a complete distortion of the Al-h spectra at high doses, making it impossible to measure the standard amplitude. We propose a new approach to measuring Al-h signal intensity, focusing on the peak-to-baseline amplitude of the part of the signal at g approximate to 2.0603, which is not affected by the peroxy signals and therefore has the potential of providing more accurate results. The shapes of dose response curves constructed for coarse and fine grains using the new approach show considerable similarity, suggesting that Al-h centre formation in fine and coarse grains upon artificial radiation at room temperature follows the same pattern.