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1

A coarse Bayesian approach to evaluate luminescence ages

Zink A.

Geochronometria

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2013

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Vol. 40, no. 2

90--100

EN

This paper develops a simplified Bayesian approach to evaluate a luminescence age. We limit our purpose to the cause-effect relationship between the age and the accumulated dose. The ac-cumulated dose is given as a function of the age and several others parameters: internal radionuclides contents, gamma dose rate, cosmic dose rate, alpha efficiency, wetness, conversion factors, wetness coefficients, fading rate and storage time. The age is the quantity we are looking for. Bayes’ theorem expresses the changes on the probability distribution of age due to the luminescence study. The in-formation before study (prior) comprises what is previously known about the age and the archaeolog-ical model (cultural period, stratigraphic relations, type, etc.) as well as the parameters of the physical model. The accumulated dose consists in the data describing the measurement. The various stages of Bayesian approach were implemented using the software WinBugs. Simulated data sets were used in various models. We present various small models representing typical exam-ples encountered in luminescence dating.

2

Uncertainties on the luminescence ages and anomalous fading

Zink A.

Geochronometria

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2008

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Vol. 32

47-50

EN

It is well known that some minerals give underestimated luminescence ages due to anomalous fading. The anomalous fading follows a logarithmic decay law characterized by its slope, the socalled fading rate or g-value. Using the fading rate, Huntley and Lamothe (2001) suggested some correction for the fading underestimation of young samples (<40-50 ka). For polymineral fine grains, we observe a fading rate of 0-4%/decade for TL and BL-OSL and 4-6%/decade for IR-OSL. Extending the laboratory observation to archaeological age, the underestimation on the age for 10 ka is estimated to a mean of 5% for TL, 10% for BL-OSL and 45% for IR-OSL. Due to the non-linearity of the Huntley and Lamothe's fading correction, the contribution of the fading to the total uncertainty is estimated by a Monte-Carlo simulation. The inference on dating shows that the uncertainty on the anomalous fading can be a significant term of the combined uncertainty on the age, even for low fading rates.

3

Luminescence dating of the Tanagra terracottas of the Louvre collections

Zink A., Porto E.

Geochronometria

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2005

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Vol. 24

21-26

EN

In connection with the exhibition Tanagra - Myth and Archaeology (Paris, 2003; Montreal, 2004), we investigated the authenticity of some 140 terracottas from the Louvre collections by luminescence dating (thermoluminescence and optically stimulated luminescence). For these terracottas being pieces from a collection, only the dose due to internal radioactivity could be derived from the direct measurement of the internal concentration of radioelements. To estimate the contribution of the external environment, we had to reconstruct the moisture content and the gamma dose rate. The moisture content was based on some indications about the site found in 19th century literature. We reconstructed the external dose rate received by the Tanagras from the ratio of the measured palaeodose to 2300 years. This result agrees well with a low radioactive soil known to be characteristic of the mainland Greece. Applying such values of the external dose rate to our Tanagra, we obtained an age distribution showing two maximums, one at 2300 š 400 years, the other at 150 š 50 years.