A portable luminescence dating instrument: a new insight for in-situ Earth applications

The age determination is crucial to unravel the evolution and to provide a framework of the geological, paleo-anthropological, and cultural conditions of a specific region of interest. The lack of chronological information makes difficult to correlate the site of interest with other temporal attributes provided by stratigraphy and paleoclimatology. Luminescence is a well-established dating technique for determining the absolute age of formation (or most recent reworking event) of geological deposits/sediments and archaeological finds on Earth, with a time range that spans from the last few decades up to one million years. The most common geological targets are dust, silt, sand, cobbles, and rock outcrops originating from different environments: aeolian, fluvial, alluvial, lacustrine, marine, glaciogenic, slope deposits, karstic, soils, tectonic activity. In the archaeological field, this technique is applied not only to the geological sediments in excavation sites but also directly to artifacts of interest, especially when they are made of pottery or stone.

A miniaturized luminescence dating prototype for in-situ examination has been designed by Alma Sistemi S.r.l., Guidonia, Italy, and validated by University of Sassari, Sassari, Italy, under European Union H2020-MSCA-RISE-2018 research programme (G.A. n.823934). The instrument is equipped with an infrared and blue optical stimulation subsystem to perform both optically and infrared-stimulated luminescence (OSL, IRSL) and is able to measure both paleo-dose and dose rate. An X-ray generator (XRG) irradiates the sample, while the response luminescence signal is obtained through a photon counting photomultiplier tube (PMT). A thermal subsystem consisting of a heater and air-cooling pumps allows the instrument to heat during SAR (single-aliquot regenerative-dose) procedure and to perform thermally stimulated luminescence. Remote control for data analysis application and a battery power supply are implemented on the instrument for usage on the field.

The development of this portable instrument is of great relevance since it finds practical use in geological and archaeological Earth's field applications. In fact, compared to current luminescence dating technologies and considering its reduced dimensions (11x11x18 cm excluding electronic box and cover) and weight (currently <5 kg), the presence of the air-cooling system Vs Nitrogen and the use of X-ray vs radiative source, qualify the instrument for direct use in the field. It is also provided with an advanced and user-friendly software tool, thus strongly reducing the need of a skilled operator. The prototype instrument has been validated using different samples and results compared with equivalent laboratory instrument (Risø TL/OSL Reader model TL/OSL-DA-20) at University of Sassari Luminescence laboratory.

At this stage, the instrument can perform a basic SAR protocol and accurately measure the response luminescence signal after different irradiations time and thus, measure the natural dose of the natural sediment sample. Here, the most recent results are presented.