Luminescence dating: a fascinating method

Camelia Bhattacharyya, Amity University Kolkata

Archaeology, anthropology, and the need to estimate dates:

The study of humans and what made them where they are today is something of great interest and it has always been this way for ages. Knowledge of the past (history) leads to a better understanding of the present and the future. So, the civilizations, the way they flourished and ended, the evolution of mankind, is something of utmost importance, not just to know but to calculate and estimate the future. The knowledge of the proper time of these developments is the most important feature for these calculations. The changes which have occurred to man over time helps to predict the ones which are still to occur in coming times (like the size of the skull, the shape of the limbs, the height of individuals, etc.). The most used methods to find these out are radiocarbon dating and luminescence dating. 

What is Luminescence dating? 

Luminescence dating was first introduced by three researchers (Farrington Daniels, Charles A. Boyd, and Donald F. Saunders) from the University of Wisconsin in the year 1953 while they tried to test thermoluminescence on some old pottery. It is a method of determining the history of exposure of a particular mineral to sunlight and heat, that is, the interval between the present and the last time it was exposed to sunlight. In this process, the energy of the photons is measured. Sediments and other archaeological and anthropological evidence (minerals and old rocks) are known to absorb certain radiations (α, β, γ and cosmic) which are the main route to tract their age by stimulating eviction of these radiations.  

Luminescence dating vs radiocarbon dating:

While radiocarbon dating can be performed only on things that were once living, luminescence dating can be done on sediments and sand since it depends entirely on minerals. Luminescence dating is thus easier and less complicated than finding substances that once lived and took carbon-14. Also, in case the organic elements get mixed with surrounding elements containing no carbon-14, the radiocarbon dating results go wrong; this is not the problem while dealing with luminescence dating. 

The equation to measure the age of a mineral:

To calculate the age of a mineral by luminescence dating method, two major parameters are to be kept in the mid. While equivalent dose (D_E) or the absorbed dose is determined by measuring the amount of luminescence being absorbed, bleached, and regenerated naturally; dose rate (D_R) is determined by activating the luminescence artificially. 

Luminescence age = (D_E)/ (D_R) is thus calculated after determining both the parameters.

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Types of luminescence dating techniques:

There are several techniques for luminescence dating. 

1. Thermoluminescence (TL),
2. Optically Stimulated Luminescence (OSL),
3. Infrared Stimulated Luminescence (IRSL).

While both TL and OSL are both performed on archaeological evidence consisting of sand and sediments with metal oxides that respond to heat and light, the former is performed with heat while the latter with different wavelengths of light. Also, OSL is mostly performed for crystal elements. Almost all three methods can be applied to components consisting of feldspar, but IRSL is specifically designed for materials like feldspar which gets activated only by infrared wavelengths. Thus, these techniques easily identify the radioisotopes of uranium, potassium, rubidium, and thorium present in the archaeological and anthropological evidence. 

Future perspectives: 

The use of artificial intelligence has been proposed in the fields of knowing history. The use of drones and 3D techniques have been into play recently to identify archaeological evidence. Researchers are trying hard to make the study procedure for historical evidence easier with time. Since the 1800s, this area has become popular while experiencing developmental techniques and studies to compile modern techniques in the study of the ancient. Till date luminescence dating is the best. Let us see what succeeds next.

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References:

1.  Daniels, F., Boyd, C.A., & Saunders, D.F. (1953). “Thermoluminescence as a research tool”. Science. 117 (3040): 343–349. doi:10.1126/science.117.3040.343. PMID 17756578
2.  Lee, M.K., Lee, Y.I., Lim, H.S., Lee, J.I., Choi, J.H., & Yoon, H.I. (2011). “Comparison of radiocarbon and OSL dating methods for a Late Quaternary sediment core from Lake Ulaan, Mongolia”. Journal of Paleolimnology. 45 (2): 127–135. doi:10.1007/s10933-010-9484-7. S2CID 128511753
3. Mejia-Bernal JR, Ayala-Arenas JS, Cano NF, Rios-Orihuela JF, Gonzales-Lorenzo CD, Watanabe S. Dating and determination of firing temperature of ancient potteries from Yumina archaeological site, Arequipa, Peru. Appl Radiat Isot. 2020 Jan;155:108930. doi: 10.1016/j.apradiso.2019.108930. Epub 2019 Oct 9. PMID: 31629293.
4. Nieto JA. Thermoluminescence of metallic oxides. Development and applications in Mexico: An overview. Appl Radiat Isot. 2018 Aug;138:35-39. doi: 10.1016/j.apradiso.2017.07.044. Epub 2017 Jul 25. PMID: 28801023.
5. Marcazzó J, Orante-Barrón VR, Camargo L, Cruz-Vázquez C, Bernal R. Optically stimulated luminescence dosimetry performance of novel MgO-La(OH)₃ phosphors. Appl Radiat Isot. 2020 Mar;157:109031. doi: 10.1016/j.apradiso.2019.109031. Epub 2019 Dec 28. PMID: 32063326.
6. Stefano Campana. Drones in Archaeology. State‐of‐the‐art and Future Perspectives. Wiley Online Library. 2017 Dec; 24(4):275-296. doi/abs/10.1002/arp.1569.

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