T. Trautmann

Spectral information from minerals relevant for luminescence dating

The paper reviews basic spectral features of luminescence from minerals used in dating and allied research. Luminescence production is a result of multiple interactions within the imperfect crystal lattice and spectral information is not limited to the emission of light. Results of spectral investigations of luminescence emission during thermal stimulation (TL) or optical stimulation (OSL) form the main part of the paper. However, information on luminescence excitation and light absorption spectroscopy is also presented and possible links between luminescence production in minerals and particular lattice defects are considered. Quartz and feldspars, the most commonly used minerals, receive special attention, but the review includes other materials such as polymineral fine-grained fractions from sediments, zircon, calcite and other salts (halite, sulfate), meteorites, flint, volcanic materials (obsidian, tephra), ceramics and metallurgical slags. Although a wide range of different luminescence emission wavebands occur, it can be shown that certain emissions dominate in particular materials. Basic dosimetric properties are often known just for single emission wavebands of a particular mineral, and are listed in this case. The paper also aims to provide a starting point and inspiration for the study of other TL and OSL emissions, with particular regard to their potential and suitability for dating and related dosimetry tasks. These investigations, involving palaeodose determination based on an emission waveband with known characteristics, need careful separation of the particular emission peak, which may be influenced by its behaviour during the dating procedure (sample preparation, irradiation, preheat treatments, luminescence measurements, etc.). Spectral information available in this context and some technical remarks on the experimental conditions will be given to pave the way for conventional TL or OSL measurements in luminescence dating and dosimetry using natural or semi-natural materials.

Feldspar radioluminescence: a new dating method and its physical background

Natural minerals, like widespread quartz and feldspars, have physical properties that enable them to be used as radiation dosimeters in quaternary geochronometry and archaeochronometry. We present a new luminescence dating method based on radioluminescence measurements of potassium feldspar. The light emitting transition of electrons from the conduction band into an optically sensitive electron trap was investigated for the first time. There are many advantages in such direct measurements of the metastable electron density in this particular trap, given that it produces an age-dependent signal. The method is able to date the last light exposure of feldspar grains in a range of a few hundred to about two hundred thousand years. Examples of age determination of different waterlaid quaternary sands are presented. A new model is introduced to explain the dose dependency of the different radioluminescence emissions. The simulations done with this model are in good agreement with the experiments. The results of a basic study of radioluminescence kinetics also show effects that are able to influence the results of luminescence dating.

Radioluminescence dating of sediments: methodological aspects

Abstract Radioluminescence (RL) at 865 nm (1.42 eV) — a characteristic of potassium feldspar — has been applied successfully in the dating of Quaternary sediments. The signal can be interpreted as the infrared (IR)-emitting electron transition into a light sensitive trap. Direct measurement of the electron density is thus possible, and this is the basic advantage of this new method. Further investigations have been carried out to develop a precise and reliable IR-RL dating procedure. Besides the already applied additive dose total bleach technique, that of total bleach regeneration and a combination of both (slide technique) were tested in the dating of different aeolian and waterlaid sediments. New bleaching experiments show that about 10 min of light exposure (about 300–700 nm) is sufficient to reach the saturation level of the IR-RL signal. Palaeodose determinations of recently deposited sediments result, in most cases, in an age equivalent to

The basic principle of radioluminescence dating and a localized transition model

The IR signal of the radioluminescence of potassium feldspars is caused by the luminescent transition of electrons into optically active traps. This allows the direct determination of the density of trapped electrons and therefore a method of sediment dating with higher precision and accuracy than conventional luminescence dating. The principle behind it and its advantages are presented, in particular the fact that it is a real single aliquot dating technique. The explanation of both radioluminescence and IR-optically stimulated luminescence (IR-OSL) in terms of a band model is possible after the introduction of a localized transition. In contrast to previous models, the process of dose accumulation in the sediment was simulated using a dose rate as low as in real sediments. Preheat experiments indicate that the recombination centres are the unstable part of the luminescence process. The parameters of these centres are equal to those previously assigned to thermally unstable electron traps. Furthermore, the sources of systematic errors in conventional IR-OSL dating are discussed.

Investigations of feldspar radioluminescence: potential for a new dating technique

The radioluminescence (RL) properties of different types of feldspar were investigated by means of spectral measurements. An increase of the radioluminescence signal can be related to the accumulated dose and seems to be proportional to the number of filled traps. Therefore the increase of the RL signal can be used for dosimetry purposes. Radioluminescence growth curves were measured for two samples to calculate the dose rate of the excitation source. Measurements, computer simulations and the principle of a new dating technique are presented.

A spectral radioluminescence study for dating and dosimetry

Abstract The spectral distribution of radioluminescence (RL) and its dose dependence was investigated on various substances to get information about the applicability in dosimetry and dating. The list comprises archaeometallurgical slag components (quartz relicts, glassy fraction), bone, cooking salt, corals, egg shell, flint, mussel shell, natural gypsum, natural halite, quartz (sediments, vein quartz) and sugar. The different emission wave-bands and basic features of their RL-dose-characteristics are reported for 18 different samples. Furthermore results of some materials are discussed in more detail.

RADIOLUMINESCENCE DATING : A NEW TOOL FOR QUATERNARY GEOLOGY AND ARCHAEOLOGY

Abstract Natural minerals, such as widespread quartz and feldspars, have physical properties which enable them to be used as radiation dosimeters. The underlying luminescence phenomena have made it possible in recent decades to determine the age of a variety of materials important for quaternary geochronometry and archaeochronometry. We present a new luminescence dating method based on radioluminescence measurements of potassium feldspar. For the first time we have been able to investigate the light-emitting transition of electrons from the conduction band to an optically sensitive electron trap. Many advantages can be derived from such direct measurements of the metastable electron density in this particular trap, which produces the age-dependent signal. The method can be used to date the last light exposure of feldspar grains within a range of a few hundred to more than 200,000 years. Examples are presented of age determination of various waterlaid quaternary sands. The results of a basic study of feldspar radioluminescence also shed light on effects not sufficiently understood in conventional dating by luminescence techniques, especially in infrared optically stimulated luminescence dating of feldspar.

A systematic study of the radioluminescence properties of single feldspar grains

Spectral radioluminescence properties of a large number of single grains were measured. The main emission in K-feldspar grains occurs in the infrared range with the same dose characteristic as shown by multi-grain samples. For plagioclases, large differences in spectral radioluminescence between single-grains and multi-grain aliquots were detected. Differences in the saturation of the dose characteristics of the individual emissions have been observed. Consequences for dating application are discussed.

Activation energies of IRSL traps in feldspars

Abstract Investigations were carried out to determined the thermal activation energy of IRSL traps with two new methods. The methods use either isothermal or hyperbolical heating functions. These functions offer an advantage because of their independence from order of kinetic in luminescence production. The selection of the three samples was made such that they exhibited a single emission and showed evidence of two trapping centres, thereby meeting the restriction of a two trap-single recombination centre model. The results and conclusion regarding the practical applicability of both methods are discussed.

A luminescence study for dating archaeometallurgical slagspaper

Abstract A reliable direct dating method for archaeometallurgic slag has not yet been achieved. Nevertheless, in archaeological and environmental research information about the age of slag deposits is urgently needed. Metallurgical slag consists of many components. Artificial secondary minerals, for example fayalit, olivine and glass phases are the dominant parts. In many cases primary minerals, called relicts, are also components of slag. Quartz, baryte and fluorite are examples. Such a complex composition leads to large difficulties in paleodose determination if the bulk slag substance is used. On the other hand, slag has a complicated microdosimetry caused by great differences between the individual mineral phases and the possibility of inhomogeneous radionuclide distribution. To overcome these problems in luminescence dating defined phases of the slag have been separated by special chemical and physical procedures. Quartz and glass fractions were investigated by thermoluminescence (TL) and radioluminescence (RL)-spectrometry. Alpha-autoradiography using Kodak LR-115 foil was carried out to get information about the distribution of radionuclides.