Luminescence Dating Laboratory
The luminescence dating started in our Department on the break
of 70' and 80'. The early work on thermoluminescence was inspired by
the late Prof. Mieczysław Pazdur and consisted mainly in measuring TL
signal from various samples using an old equipment for mineralogical
studies. At that time when basic experimental experience was gained an
effort was made towards designing and constructing TL reader more
suitable for measuring faint light signals from small aliquots of
quartz, feldspar or calcite grains. The first TL reader was constructed
as a manual unit with analogue controls. The gained photomultiplier
output was directed to the XY recorder and recorded thermoluminescence
glow curves were digitised prior to further calculations. At this early
stage collaboration with the Physics Department in the Institute of
Oncology in Gliwice gave access to calibrated gamma ray sources used to
additional irradiation of grains extracted from geological samples. The
three-channel gamma scintillation spectrometer was available in the
Solid State Physics Department and used for samples natural
radioactivity assessment. This equipment enabled first TL dating to be
performed in 1983. Later works were concentrated on refining laboratory
procedures for sample preparation, automated data taking and storing
and developing software tools data reduction and calculations. The new
version of the TL reader was built in 1985. It was completely
redesigned. The light collection was improved making possible
measurements of TL from calcite samples and from quartz grains extracts
from very young sediments. The TL reader was directly controlled by the
computer system consisted of the CAMAC crate with an autonomous
controller and several specialised digital units. The linear heating
was achieved through applying a digital to analogue converter driven by
the system controller. Temperature and PMT current signals were
digitised and stored in the core memory. The CAMAC system included a
serial communication unit through which it was connected to the main PC
computer responsible for the whole measurement process. The PC sent
primitive commands to and received data from the CAMAC controller. This
computer controlled version had much better stability and
reproducibility, and was much more convenient in routine use. TL glow
curves were now stored in a digital form as computer files and were
available to the originally developed computer programme which
performed all the calculations and made graphic presentations of
original and reduced data.
Some solved important problems
Investigations into the efficiency of mechanism of zeroing pregenetic TL in aeolian sediments. The studies were carried out on samples of dune sands dated independently by 14C method. The findings of this research project indicated possible overestimation of absorbed dose value and consequently the TL age for aeolian sediments up to 5 Gy or 10 ky.
Study of thermoluminescence sensitivity changes of mineral grains caused by optical bleaching. The study was carried out on a set of geological samples of different origin. The bleaching was done by exposure to natural unfiltered sunlight and to artificial filtered light from the mercury lamp. The changes in sensitivity were detected by means of the Snydecor's F-variable statistics in 20% of studied samples.
Comparison of TL dates obtained for a set of samples from the well known loess profile in Odonów, Southern Poland. Multiple samples taken from the same loess layers were dated independently in three TL laboratories by different techniques. The results of this interlaboratory comparison project showed that TL dating results could be severely biased by specific laboratory procedures adapted in the laboratory while differences found for soil layers may be related to soil development processes. The issue of comparing results of dating geological objects by different absolute methods was further investigated within the project where 14C, ESR and TL dating methods had been applied to speleothems from caves in the Tatras.
Bootstrap method in statistical analysis of dates. The possibility of bootstrap method application in an interpretation of radiometric dating results had been investigated. The research concerned date assemblages obtained for single geological or archaeological objects as well as aggregates of such objects. The total frequency distribution of greater number of dates usually shows multiple maxima and minima. In a case of geological samples of appropriate type these minima and maxima may be interpreted as corresponding to periodic climate changes. In a case of archaeological samples the periods of characteristic cultures or periods of certain area inhabitation may be established in an objective way. The bootstrap method enabled assessment of statistical significance of the observed distribution maxima.
Influence of disequilibrium in the uranium
series on TL and ESR dates of speleothems. The goal of this study
was to find the relationship between actual radiation dose absorbed by
the speleothem from the moment of its formation till now, and that calculated
Measuring very small doses of ionising radiation using natural quartz as dosimeter. It was shown that using natural quartz grains extracted from selected samples and making TL or OSL measurements following single aliquot protocols absorbed dose values of the order of 1 mGy or below may be assessed with a good accuracy. These investigations were of a great importance for retrospective dosimetry of accident doses.
Combined OSL/TL dating of geological samples was proposed as a new method giving possibility of assessing the degree of bleaching the mineral grains in the dated sediment underwent during its formation. The method takes advantage of the fact that the OSL measurement does not reduces significantly TL signal measured directly after it. It was shown that the same set of aliquots may be first measured by OSL method and then by the TL method, yielding to estimates of absorbed dose value. Taking into account the fact that OSL signal is much more efficiently bleached by light (matter of minutes instead of hours or days as in the case of TL signal) the difference in both dose estimates may be expected if sample underwent a relatively short exposure to light. Long exposures should result in well bleached grains and consequently no difference should be found between OSL and TL derived values of absorbed dose. Because OSL and TL are measured exactly for the same aliquots there is no other possible sources of divergence and the observed difference of absorbed dose values may be interpreted in terms of bleaching efficiency and conditions under which sedimentation took place.
OSL dating of geological sediments by the single aliquot regenerative and additive dose protocols. The OSL dating of geological sediments using single aliquot additive dose and regenerative dose protocols has been successfully introduced into the laboratory practice. By using specially designed measurement protocols one is able to perform all the necessary OSL measurements and laboratory irradiation on a single aliquot (the limit of aliquot size is eventually a single grain) and finally obtain the absorbed dose value. This method enables investigations of distribution of absorbed dose if a number of single aliquots is measured. The shape of the distribution enables conclusions regarding the origin of the sediment and processes involved in its formation.