Untitled Project

Methods

Summary

Optically stimulated luminescence (OSL) dating is based on the emission of light from natural minerals that have previously been exposed to natural ionizing radiation (Athanassas and Wagner, 2016). OSL is very useful in archaeology because it can date the time of manufacturing of ancient clayware, or the deposition of archaeological sedimentary layers. 

Natural ionizing radiation is expressed as radioactivity, emitted from decaying isotopes that are ubiquitous in the environment, and the contribution of cosmic radiation impinging the Earth surface from all directions. 

Mineral grains of quartz and feldspar, which are abundant in archaeological materials, can memorize their exposure to ionizing radiation: the longer the exposure the stronger their OSL signal.  The OSL signal is very sensitive to sunlight (direct or indirect), and even a brief shine can zero OSL almost instantaneously. Zeroing of OSL is termed "bleaching". For this reason OSL constitutes a chronometer of the time elapsed since the last exposure of sedimentary grains to sunlight. This necessity is met for sediments from archaeological layers (Athanassas et al. 2015) and sun-baked bricks (Duller, 2008).

Challenges

Sample collection for OSL dating will include extraction of small but sufficient amount of grains from the mudbricks in a non-destructive way. Besides, sampling of layers will be carried out by introducing light-tight (aluminum/PVC) tubes into an already excavated soil profile underneath the structure. 

In case of crumbling sediments, samples will be collected at night to avoid the risk of exposing the sediment to sunlight, by delving into the soil profile with a spade and then sealing the samples in opaque casing.