Seminer Duyurusu

Luminescence applications in natural sciences and engineering

 Dr. George S. Polymeris

Institute of Nuclear Sciences, Ankara University, Ankara, Turkey )

 17 Şubat 2014

Saat : 10:30

Nükleer Bilimler Enstitüsü

 Abstract

Luminescence, in both forms of thermoluminescence (TL) as well as optically stimulated luminescence (OSL), has been increasingly used for dosimetric purposes that presently constitute an important part of solid-state dosimetry. In the procedure of luminescence, the target samples are exposed in the laboratory to the appropriate stimulation source (heating or light of appropriate wavelength in the cases of TL and OSL respectively). Luminescence is thus emitted during the stimulation period, the integral of which provides a measure of the dose of radiation absorbed by the dosimeter. Through calibration of the signals against known doses of radiation, the absorbed dose can be obtained. Luminescence dosimetry has been actively developed in the past 4 decades thanks to its successful applications. Among them, the most widespread is the so called retrospective dosimetry, which falls in two major categories, namely the geo-archaeological dating and the accidental dosimetry. The target material in those cases consists of grains of naturally occurring minerals, usually quartz and/or feldspar; however in some cases salt as well as Ca-based materials work also very efficiently. A separate determination of the environmental dose rate is required in order for the age of the sample to be determined. A brief overview of the main aspects of luminescence dating, along with a number of successful luminescence dating applications will be presented, while special attention will be paid to some ongoing trends towards dating of megalithic structures, paintings, marbles and glasses. Nevertheless, luminescence dosimetry is also applied to sterilization dosimetry. Herbs, spices and medicine are sterilized by the use of large doses (of the order of 1-20 kGy). Luminescence stands as a unique tool to assess these doses. Typical examples will be presented.

In recent years, luminescence dosimetry has been used on ever growing scale in cases of radiation therapy, radiation monitoring of personnel working around sources of ionizing radiations and as well as the radiation monitoring of the environment. The aforementioned successful applications of luminescence dosimetry stemmed from the search, development, and analysis of properties of artificial materials which were fabricated for detectors of ionizing radiations. A brief overview of the properties of those artificial luminescent dosimetric materials will be presented, along with some general approaches to the search for and the development of new efficient dosimetric materials. The impact of (a) a very stable luminescence signal, arising from very deep traps (VDT) and (b) the de-convolution procedure will be discussed for all aforementioned applications.

Nevertheless, the traditional field of applications of luminescence has been considerably expanded besides dosimetry. TL is also an established tool of engineering towards the solid-state characterization of several materials as well as the detection of phase transitions. In the framework of this presentation, special emphasis will be given to a number of alternative applications of TL (and some case OSL as well) as a probe for:

  • Study of ancient pottery manufacturing technologies by assessing their firing temperature in the past.
  • Provenance studies in the cases of crystalline quartz, amorphous silica glasses, obsidian and gemstones of archaeological interest.
  • Structural state characterization of feldspars.
  • Bioactivity study of artificially manufactured bioactive glasses for osteo-inductive and osteo-conductive purposes.
  • Characterization studies of properties of nano-structured materials, such as dosimetric Al2O3:C as well as thermoelectric Mg2Si.
  • TL applications in the study of micro-meteorites.