Nucl. Tracks Radiat. Meas., Vol. 18, No. 4, pp. 425-426, 1991 Int. J. ~_o~ot. Appl. Instrum., Part D Printed in Grcat Britain

0735-245X/91 $3.00 + .00 Pergamon Press pk

CONFERENCE REPORT

6th INTERNATIONAL SPECIALIST SEMINAR ON TL A N D ESR DATING

held at Clerrnont-Ferrand, France, August 1990

Sxr.ptn~ Sxor,~s

Research Laboratory for Archaeology and History of Art, and School of Geography, Oxford University, 6 Keble Road, Oxford OXI 3QJ, U.K.

A TOTAL of 36 oral and 55 poster presentations were given at the meeting on luminescence dating and related studies [incorporating both thermo- luminescence (TL) and optically stimulated lumin- escence (OSL)]. The considerable number and variety of subject material within the presentations, and the lively discussion, both in formal sessions and within informal groups, reflect the considerable expansion and development within the field since the last specialist TL/ESR Seminar held in Cambridge in 1987. As with the previous meeting, the proceedings of the seminar have been published in .volumes of Nuclear Tracks and Radiation Measurements (3/ol. 18, No. 1/2) and Quaternary Science Reviews, the sub- division into the respective journals being based on the relative physical versus geological/archaeological contents of the presentations.

The dosimetry and luminescence properties of quartz, feldspar, zircon and fine-grained polymineral mixtures were well represented within the presenta- tions. Franklin et al. (University of Maryland) dis- cussed the selective use of a rapidly bleachable trap in quartz which exhibits an emission at a wavelength of approximately 380 nm. The signal from this trap (which occurs at ~290°C when heated at I°C s -~) was isolated by the use of UV filters (e.g. Sehott UG11) and a subtraction technique was used to esti- mate the palaeodose with the regeneration method. It should be noted that this trap is a major donor in quartz OSL where its rapidly bleachable behaviour is utilized by selective excitation using green (:. ffi 514 rim) light. A number of presen: .tions further dis- cussed the applicability of coarse-grained potassium feldspar as a stable TL and OSL dosimeter over archaeological and geological timescales, with Mejdahl (Rise National Laboratory, Denmark) and Rendell (University of Sussex, U.K.) both describing successful TL age evaluations for independently dated se- quences, whilst Balescu et al. (University of Quebec, Canada) and Duller (University College of Wales,

Aberystwyth, U.K.) reported some systematic under- estimation of true age for TL and IRSL (infrared- stimulated luminescence, ,l -- 880:1:80 nm), respect- ively. Despite the underestimations discussed, the lack of saturation in the potassium feldspar signal, even in the oldest samples (c. 300ka) measured prompted optimistic comments from the authors. Refinements to the auto-regenerative dating of zircon were discussed by Smith et al. (Oxford University, U.K.), who have developed equipment which incor- porates an imaging photon detector (IPD) in the place of a conventional photomultiplier. The advan- tage of the IPD is that it allows measu~e~ent of TL directly from individual grains and avoids the effects of both dark current and black body radiation from all other regions. As is commonly the case at the seminar, numerous reports on the dating of loess deposits from Europe and China using fine.grained polymineral sediment fractions were presented.

Several papers were presented on luminescence emission spectra from a variety of minerals. Of particular interest were the light-induced emission spectral studies of Huntley et al. (Simon Fraser University, Canada) who confirmed a UV (,l = 365 _+ 60 rim) emission band for quartz and noted its contrast to the 350°C TL spectra, and outlined general emission bands for feldspars at wavelengths of 330, 400 and 570 nm. They found that the 400 nm band is particularly strong for potassium feldspars and that the 570 nm band is strongest for plagioclase feldspars. Similar results for potassium feldspars were found by Jungner and Huntley (University of Helsinki, Finland) when excited by a He-Ne laser (:. = 633 nm).

For the first time, a number of presentations compared the luminescence response of various dosimeters to optical and thermal excitation. Spooner (Oxford University, U.K.) found a close correspond- ence for both the sensitivity and short-term anom- alous fading behaviour of a selection of feldspars of

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426 S. STOKES

widely differing compositions. Stoneham and Stokes (Oxford University, U.K.) found a strong correlation between dose-dependent sensitivity change in sedi- mentary quartz OSL (using green light stimulation) and dose-dependent sensitivity changes in the 110°C quartz TL peak. The possible use of the 110°C quartz TL peak as a monitor of OSL sensitivity change, and as a potential OSL normalization method, were discussed. Hutt and Jungner (Institute of Geology, Tallin, U.S.S.R. and University of Helsinki, Finland) presented an intercomparison of the dating of kames by IRSL and TL. They found that in the majority of cases the degree of optical bleaching during depo- sition was insufficient for either method. In one case, however, an IRSL equivalent dose evaluation pro- vided an acceptable date where the TL equivalent close indicated insufficient bleaching.

Over 30 papers considered the application of both TL and OSL in a wide, dominantly terrestrial, spectrum of depositional environments. Ongoing dat- ing of desert sequences from a range of geographical localities were outlined. Singhvi et al. (PRL, Ahmadabad, India) discussed new TL results for the hot climate Thar desert, while Dijkmans and Wintle (University of Utrecht, Netherlands, and University College of Wales, Aberystwyth, U.K.) presented results of their investigations on the age of the cold climate aeolian sand sheet of the Netherlands. In addition to these and the loess investigations mentioned above, Stokes (Oxford University, U.K.) reported the findings of an investigation into the OSL age of a variety of young (modern) aeolian sub- environments. The results indicated that residual OSL levels at deposition imply residual depositional ages of the order of tens to hundreds of years---a considerable advantage over conventional TL dating of sediments. The use of TL in an extensive investi- gation of littoral (shallow marine) sediments was presented by Castagnoli (Institute of Geophysics, Torino, ltaly). Cyclicity observed within the indepen- dently dated sequences was inferred to relate to solar cycles on approximately 100-yr periodicities. Variably successful TL dating of river terraces to ages of up to around 120 ka were reported by Proszynska-Bordas

and Stanska-Proszynska (Warsaw, Poland). Addi- tional fluvial samples dated by TL from the Amazon Lowland were provided by Ervanne et al. (Helsinki, Finland) and the first application of IRSL to the dating of young (I-5 ka) colIuvial and alluvial samples was presented by Aitken and Xie (Oxford University, U.K.), with considerable success being reported. Investigations into the re-setting of detrital grains during glacial and glacial-marine transportation were outlined by Forman and Ennis (INSTAAR, Uni- versity of Colorado, U.S.A.) and by Lamothe and Marcheterre (University of Quebec, Canada). Unfor- tunately it would appear from these studies that a TL-based dating method for such material remains unavailable at the present time.

The development of a wide range of automated systems, or modifications of pre-existing systems for either TL, OSL, or both, were discussed and a number of recently developed pieces of equipment were on demonstration at the conference centre. In particular, in response to the recent investigations undertaken on IR stimulation of feldspathic minerals by IR diodes as a relatively cheap means of optical dating, a number of systems incorporating IR diode arrays were discussed, both by major manufacturers of TL equipment including Daybreak, Littl~more Scientific and Ris~ National Laboratories, and by Galloway (University of Glasgow, U.K.). A novel modification and application of the recently devel- oped IRSL technology for the continuous monitoring of sediment cores was presented by Duller et al. (University College of Wales, Aberystwyth, U.K.). Ichihara et al. (Osaka University, Japan) also reported equipment developments in the form of a battery-operated, gas-heated, portable TL detector.

The considerable information which conference delegates gained and the interaction between delegates which was possible while in Clermont-Fen'and can to a large degree be attributed to the excellent formal meetings and social activities co-ordinated by the local organizing committee headed by Drs Fain and Miallier. Delegates will retain fond and fruitful memories of the time which they spent in the shadow of the Chaine des Puys.