Luminescent Age Dating Laboratory

OSL (Optically Stimulated Luminescence) is a feeble emission of light brought about by the release of energy absorbed by the material that was stimulated by light. OSL age dating is based on the fact that charges (electrons or holes) are trapped in the defects of the minerals crystal-lattice. On the surface the light-sensitive traps would be emptied on the sunlight. Isolated of light following burial after deposition the traps slowly become recharged through ionising radiation coming essentially from the decay of the radioactive isotopes (K, U, and Th) of the host sediments and subordinately from cosmic rays. The charge of the traps increases proportionally with the growth of the intensity and duration of ionising radiation.

In the Geological Institute of Hungary using the RIS TL/OSL DA-15C/D luminescent age dating unit made in Denmark the luminescence of quartz grains of the sand fraction is measured applying blue-light illumination and laboratory ß radiation emitted by Sr-90 source. The measurements are performed according to the extensively used SAR (Single Aliquot Regenerative Dose) protocol.
Based on the OSL measurement of quartz grains the absolute age of the deposition and formation of sedimentary assemblages mostly younger than 100 000 years can be determined. It is a considerably wider interval than in the case of radiocarbon age dating. This method can also be used for dating the age of environmental events having occurred in historical time provided they can be associated to sedimentary features.

Sampling

: isolated of light with dark PVC tube from aeolian and fluvial sand, silt as well as loess, exposure and borehole.

Sample preparation

: separation of 1-2 mm quartz grains by sieve, heavy liquid and chemicals (H2O2, HCl, HF) in dark at dim red light.

Luminescent measurements:

Determination of the palaeodose equal to the dose of radioactive radiation absorbed from the host sediments and subordinately from cosmic rays, according to the SAR protocol on 18 and 100 sub-samples for older and younger sediments, respectively. (Complementary measurements: IR test, preheat plateau test, dose recovery test, dose response grow curve, thermal transfer test)

Gamma spectrometric measurements.:

The measurement of the radiation of the host sediments for determining the radioactive radiation affecting the sediment in unit time i.e. dose ratio is performed by the staff of the Eötvös Loránd Geophysical Institute.
Determination of the actual and saturated water content of the sediment and its estimation for the period of burial as well as the calculation of cosmic radiation for the given location in order to determine the dose ratio.

Calculation of the OSL age:

palaeodose (Gy) / dose ratio (Gy/thousand years).

For more information please, contact:

Dr Annamária Nádor and Dr Thamóné Edit Bozsó
Geological Institute of Hungary
Budapest, 1143 Stefánia út 14.
Phone: (+361) 267-1428, Fax: (+361) 251-5669
Email: nador@mafi.hu, bozso@mafi.hu