ESR dating of quartz grains: evaluating the uncertainty associated to ESR measurements at low temperature

Abstract

While ESR dating of quartz has progressively become quite a popular application in Quaternary sciences over the last couple of decades, as attested by the increasing number of dedicated laboratories and research groups around the world, there are still no unified or standardised measurement procedures within the ESR community. Quartz differs from other materials typically measured by ESR (e.g., tooth enamel, carbonates, alanine), in the sense that it has never been subject to any interlaboratory comparisons, and ESR measurements are significantly more challenging due to nature of the material, its heterogeneity and the experimental conditions involved. In particular, radiation-induced signals used for dating purpose are only visible at cryogenic temperature. The truth is that each laboratory uses its own analytical procedure, and there is no general consensus at a community level about the best laboratory practices for the ESR measurements at low temperature. For example, there is a significant variability as far as equipment used, measurement temperatures employed, experimental conditions or even how the ESR intensities are measured. This variability makes it extremely complicated, or even impossible, to directly compare results obtained from different laboratories. As a result, the true uncertainty associated to ESR measurements is currently unknown.

In this talk, I will try to provide some initial insights into this uncertainty, with an overview our methodological investigations carried out at CENIEH over the last decade. We have been specifically aiming to identify the various sources of uncertainty involved in the ESR measurements of quartz, and quantify their potential impact on data outputs. These sources of uncertainty are mostly related to (i) the experimental conditions (e.g., experimental setup, acquisition parameters, measurement temperature), (ii) the sample itself (e.g., homogeneity, variability of the ESR spectra), (iii) or the data reduction process (e.g., measurement of ESR intensities, baseline correction, signal to noise ratio). A special emphasis will be given to measurement repeatability, and about the importance of carrying out repeated measurements of a given sample.

Acknowledgments: This work would not have been possible without the input and feedback from all the staff, students and researchers working in the laboratory over the last 15 years, with a special mention to V. Guilarte, M.J. Alonso Escarza, M. Bartz, M. del Val and E. Ben Arous.