Information for Prospective Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) Users

Introduction | Section I | Section II | Section III | Section IV | Section V | Other U.S. Labs

Section IV: How to Collect Samples for TL and OSL Dating

Sampling Equipment


How *not* to sample.

In general, try to avoid sediments that show any post-depositional disturbances such as root penetration, krotavinia (bioturbation), carbonates, ground-water leaching, certain soil formations or large stones that may hamper sampling. If the only exposure that is available is one in which cracks, roots or krotovina may be encountered at depth, or the sediment is so hard that it will be difficult to remove a tube driven in at depth, then take a cube block sample at the site. Mark the sample as to the side exposed to the surface. Wrap it in aluminum foil, a black bag (several layers if being shipped) and tape tightly to prevent disintegration.

Ideally, a 0.5 meter (about a one-foot hole) must be augured into the soil sample above or below the boundary of the layer so that the luminescence and bulk samples are taken or counted on a homogenous layer. If this is not possible, take the luminescence sample and dig sideways for adequate bulk sample sediment. Sampling tubes of either 0.15" wall PVC (white or black) or steel should be driven into the back of the hole to collect the luminescence sample. PVC tubes often benefit from a sharpened or beveled edge on the back of the tube to be driven into the sediment. Tubes are driven in by sledgehammer, however, a hard metal plate should be used against the end being hammered to prevent shattered or collapse.

If the sample is being collected during the daylight hours, a black or opaque cloth MUST be used to shield the sample collection and the immediate site from light upon removal of the sample. If the sample is collected at dusk or night, a red-filter light can be employed at a minimum for collector's visual aid. The lab will need about 50 grams of sediment if the sample is fine-grained, about 75 to 100 grams if the sample is sand-size for adequate replicate analyses.

The sample tube should then be carefully pried or dug out from the hole by pushing a knife or chisel alongside the tube and levering it sideways. Cover the sample hole with a black cloth (this may require the aid of others) while freeing the tube. Once the tube is free, DO NOT remove it from the hole or black cloth until the open end is closed with a black cap or duct tape. Both ends of the tube can then be sealed with black electrical tape if the caps look loose or if they might pop off during sample shipment. Place the tubes in a black polyethylene black bag (the kind used in photography supply stores and not black trash bags). Write the sample name on both tube and bag.

A second sample must be collected from the back or sides of the same hole. This sample, referred to as the "bulk sample", does not need protection from light. The bulk sample should be collected in a double Ziploc 1 quart size bag to inhibit the loss of moisture, so that gross moisture content can be measured in the lab. This sample can also be used to obtain a DR if field analysis is not possible. In that case, at least 600-grams of sample is needed for the gamma ray counting.

Photographs or trench logs showing the locations of samples should be included if possible. Usually one photograph is required to locate the sample hole in stratigraphic context and one close-up to show texture of the sediment sample. The augured holes often show up well in distant photos of the site. Location of the site using GPS systems is appreciated and depth of sample below the original surface of the ground should be noted, as these are needed for a calculation of cosmic ray component of the DR.

Other materials that can be collected to date archeological finds using luminescence:

1. Artificial Glass: There have been few successful attempts, caused principally by glass' non-crystalline state. TL and OSL can only used if glass has not been heated above "glass transition" temperature (? ° C). (Mueller, P. and Schvoerer, M., 1993, Archaeometry 35: pp. 299-304, Factors Affecting the Viability of TL Dating of Glass).
2. Burned Flint and Stones: Well suited for TL, especially in dating Middle to Lower Paleolithic periods. Zeroing requires 450°C and this assumption can be tested for. Oldest age obtained is 453 ±39 Ka. (Richter, D.G., 1997, Dissertation for University Tubingen, in German, no translation).
   
   Potboilers (heated stones) have also been successfully dated. (Huxtable, J., Aitken, M. J., Hedges, J. W., Renfrew, A. C., 1976, Archaeometry 18: pp. 5-17, Dating a Settlement Pattern by TL: The Burnt Mounds of the Orkneys).
3. Ceramics and Burnt Clayware: Important concepts of TL methods were established on ceramic shards, bricks and kilns during the 1960's and 1970's. The usual method is to date both polymineralic fine-grains (4 to 11 ±) and quartz coarse-grains (100-200 µ), thus combining TL ages. Typical error is 6-10%. (Wagner, G.A. and Lorenz, I. B., 1997, another untranslated German paper).
   
   Medieval kiln structures or the burned surface lining (containing quartz) have been successfully dated (Wagner, G. and Wagner, I., 1994, another untranslated German paper).
   
   Authenticity dating of ceramic objects uses both TL and OSL. For TL, the lab needs 200 mg of powder and only really looks for baseline signal, indicating recent age or a natural TL glowcurve, indicating some elapsed time greater than 500 years. (Aitken, M. J., 1985, Thermoluminescence Dating, Academic Press, 359 p.). For OSL, 100 mg or less is needed and higher precision of measurement gives 1-2% error if the single-aliquot method is used. (Mejdahl, V. and Botter-Jensen, L., 1997, Radiation Measurements 27: pp. 291-294, Experience with the SARA OSL Method).
   
   Success in using the quartz extracted from fired bricks has been obtained, recently in using Chernobyl exposed bricks to the increased radiation during the accident as "dosimeters" for reconstruction of dose rates (Banerjee, D., Botter-Jensen, L. and Murray, A.S., 2000, Applied Radiation and Isotopes 52: pp. 831-844, Retrospective Dosimetry: Estimation of the Dose to Quartz Using the Single-aliquot Regenerative-dose Protocol).
4. Slags: Attempts have been made to date archeometallurgic slag by TL, but the glass phase is problematic. Since slags consist essentially of silicates, heated to high degrees, in theory even OSL should work. Uncertainties about DR, however, render errors at 20%. (Elitzsch, C., Pernicka, E., and Wagner, G. A., 1983, PACT 9: p. 271- 286, TL Dating of Archeometallurgical Slags).
5. Vitrified Forts or Earth Mounds: Prehistoric walls consisting of vitrified quartz and feldspar bearing rocks are of widespread occurrence in western Europe and TL ages have been obtained from Scotland. (Sanderson, D. C. W., Placido, F. and Tate, J. O., 1988, Nuclear Tracks and Radiation Measurements 14: pp. 307-316, Scottish Vitrified Forts: TL Results for Six Study Sites).
   
   In northeastern Louisiana Paleo-Indian earthworks have been dated, presuming exposure to sunlight during construction or occupation of the mound. Dating was by means of OSL using 90-120 µ quartz. Insufficient bleaching proved to be a problem, even with OSL, but minimum ages were obtained (Feathers, J. K., 1997, Quaternary Geochronology 16: pp. 333-340, Luminescence Dating of Early Mounds in Northeast Louisiana).
6. Wasp Nests: Using OSL to date quartz grains imbedded in petrified mud-wasps nests is a new way to give dates to rock petroglyphs and paintings. Nest thickness need to be at least 5mm and in some cases, an experimental method of single-aliquot analyses (due to lack of material) gave excellent results. Ages up to 16.4 Ka were obtained with about 10% error. (Roberts, R., et. al., 1997, Nature: vol. 387, pp. 696-699, Luminescence Dating of Rock Art and Past Environments using Mud-wasps Nests in Northern Australia).

Other materials that can be collected to date geological sediment using luminescence