VAKGROEP GEOLOGIE EN BODEMKUNDE

Geochronology Group

 

Luminescence Dating

 

Research team

Professor : Peter Van den haute

PhD Student : Jan-Pieter Buylaert

Technician : Jochem Temmerman

 

History

The luminescence-dating laboratory was installed in 1993 as a collaboration between the Laboratory for Mineralogy and Petrology (Geological Institute) and the Laboratory of Analytical Chemistry (Institute for Nuclear Sciences, INW). The co-operating scientists at the INW are Prof. Dr. Frans De Corte and PhD. students Dimitri Vandenberghe and Syed Hossain.

In general, the activities of the group have developed as follows:

1992-1995: implementing the thermoluminescence laboratory, performing authenticity testing and dating of ceramics.

1996-2001: age determination of the Late Pleistocene loess of eastern Belgium with TL

1997- 1998: Age determination of tropical sand dunes with TL

1999 - present: implementing OSL dating and age determination of the Dutch coversands

2002 - present: TL and IRSL dating of Chinese loess deposits

 

The Luminescence Dating Method

Luminescence dating is based on the measurement of the amount of light that is released upon thermal or optical stimulation, by minerals such as quartz and feldspar. The light signal is a measure of the radiation dose that has accumulated in these minerals through time.

When they are exposed to sunlight during transportation in the air the latent luminescence signal in the quartz and feldspar grains is bleached down to a negligible level and the luminescence "clock" is set to zero. After deposition of the grains and burial under new sediment, their latent luminescence signal accumulates again because they absorb the natural ionising radiation that is emitted by the surrounding sediment. The flux of ionising radiation (a -, b -, g -rays) is produced by the very low concentrations of uranium (235U, 238U), thorium (232Th), potassium (40K) and 87Rb in the sediments. A small amount is cosmic radiation. The total radiation dose that is accumulated in this way is called the palaeodose.

The age that is determined corresponds to the time span between the removal of the luminescence signal by sunlight just before deposition and the removal of the newly accumulated palaeodose by thermal or optical stimulation in the laboratory. Stimulation by heat is called thermoluminescence (TL) and stimulation by light, optical stimulated luminescence (OSL). OSL has two major variants: the infrared stimulated luminescence (IRSL) and the blue light stimulated luminescence (BLSL).

The age equation can be written as:

Thus, luminescence dating involves the determination of two major parameters: the palaeodose and the annual dose.

Reliable age determinations can be obtained from 0.1ka  to 200 ka. Typical errors are in the range of 5 to 10 %.

 

Equipment

Our sample preparation laboratory is equipped with a magnetic separator and heavy liquid (sodiumpolytungstate) separation tools to isolate and clean the appropriate grain size fractions for each sample under darkroom conditions.

Palaeodose determination (Instruments installed at the Geological Institute)

Ris° TL/OSL-DA-12 reader equipped with a 40mCi 90Sr/90Y b -source, a blue LED stimulation system (470 30 nm) and an IR laser (830 10 nm)

Ris° TL/OSL-DA-15 reader  equipped with a 40mCi 90Sr/90Y b -source, a blue LED stimulation system (470 30 nm) with signal ramping and IR LED array (870-880 nm)

Elsec 712 alpha-irradiator equipped with six 182 ÁCi 241Am alpha sources

H÷nle SOL2 solar simulator

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Loading the Ris° TL/OSL-DA-12 luminescence reader.

 

Dose rate determination (Instruments installed at the Institute for Nuclear Sciences)

six Elsec7286 low-level alpha counters 

Ris° GM-25-5 low-level beta GM multicounter system

low-background extended-energy range HPGe gamma spectrometer

portable gamma spectrometer (Canberra portable plus model 1150) and 3x3 inch. NaI(Tl)detector)

Automated Elsec 9022 irradiators (64 samples) equipped with a 182 ÁCi 241Am alpha source and a 100 mCi 90Sr/90Y beta source. (for palaeodose determination)

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The portable NaI(Tl) gammaspectrometer in action

 

Present research areas and perspectives

Chronostratigraphy and luminescence dating of the aeolian deposits of the western Chinese loess plateau: a contribution to the investigation of the terrestrial record of the Quaternary climate oscillations. (J.P. Buylaert).

Since a few years we shifted from thermal signal stimulation to optical stimulation and focussed our research on the applicabilty of the recently developed single aliquot dating procedures (SAR, SAAD). This focus wil not change during the coming years 2003-2004..

 

External services

Authenticity testing of ceramics with the TL method can be carried for museums and scientific institutions upon request.

 

Doctoral dissertations

Vancraeynest L. (1998) Bijdrage tot de studie van de thermoluminescentie-dateringsmethode en toepassing op archeologisch keramiek en eolische sedimenten. (defended at the Laboratory of analytical chemistry)

Munyikwa K. (1998) The stratigraphy, sedimentology and thermoluminescence dating of the Upper Kalahari beds of western Zimbabwe.

Hossain S. (in preparation) A critical comparison and evaluation of methods for determination of the annual radiation dose in luminescence dating of sediments. (to be defended at the Laboratory of analytical chemistry)

Vandenberghe D. (in preparation) A study of the optical stimulated luminescence dating method and its application to young geological sediments. (to be defended at the Laboratory of analytical chemistry)

Buylaert J.P. (started in 2002) Chronostratigraphy and luminescence dating of the aeolian deposits of the western Chinese loess plateau: a contribution to the investigation of the terrestrial record of the Quaternary climate oscillations.

 

Articles in international Journals (period 1998-2002)

Van den haute P., Frechen M., Buylaert J.P., Vandenberghe D. and De Corte F. - The last Interglacial palaeosol in the Belgian loess belt: TL-age record. Quaternary Science Reviews. (accepted)

Vandenberghe D., Hossain S.M., De Corte F. and Van den haute P. - "Investigations on the origin of the equivalent dose distributions in Dutch coversand" Radiation Measurements. (accepted)

Vandenberghe D., Kasse C., Hossain S.M., De Corte F., Van den haute P., Fuchs M., Murray A.S. Exploring the methodology of optically stimulated luminescence dating and comparison of optical and 14C ages of Late Weichselian coversands in the southern Netherlands. (in preparation)

Hossain S.M., De Corte F., Vandenberghe D., Van den haute P. (2002) - A comparison of methods for the annual radiation dose determination in the luminescence dating of loess sediment. Nuclear Instruments and Methods in Physics Research A 490, 598-613.

Vandenberghe D., De Corte F. and Van den haute P. (2000) - Observations on the thermoluminescence signal induced by alpha irradiation. Radiation measurements, 32, 813-817.

Muniykwa K., Van den haute P., Vandenberghe D. and De Corte F. (2000) - The age and palaeo-environmental significance of the Kalahari sands in western Zimbabwe: a thermoluminescence study. Journal of African Earth Sciences; 30, 941-956.

Van den haute P., Vancraeynest L. and De Corte F. (1998) – The late Pleistocene loess deposits of eastern Belgium: new TL age determinations. Journal of Quaternary Science, 13, 5, p. 487-497.