Buylaert, Jan-Pieter

Jain, Mayank

Kook, Myung Ho

Lapp, Torben

Murray, A.S.

Thomsen, Kristina Jørkov

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 19, 2017Review of new facilities on a TL/OSL reader for retrospective dosimetryLapp, Torben; Jain, Mayank; Kook, Myung Ho; Thomsen, Kristina Jørkov; Murray, A.S.; Buylaert, Jan-PieterPublication date:2013Link back to DTU OrbitCitation (APA):Lapp, T., Jain, M., Kook, M. H., Thomsen, K. J., Murray, A. S., & Buylaert, J-P. (2013). Review of new facilitieson a TL/OSL reader for retrospective dosimetry. Abstract from 17th International Conference on Solid StateDosimetry, Recife, Brazil.Review of new facilities on a TL/OSL reader for retrospective dosimetry  T. Lappa, M. Jaina, M.H. Kooka, K.J. Thomsena, A.S. Murrayb, J.P. Buylaerta,b  aCenter for Nuclear Technologies, Technical University of Denmark, Risø Campus, Roskilde, Denmark bNordic Laboratory for Luminescence Dating, Aarhus University, Risø Campus, Roskilde, Denmark  Email of corresponding author: tlap@dtu.dk   This presentation summarises recent major im-provements and new attachments to the Risø TL/OSL reader. These have mainly been in response to the ever growing need (i) for higher precision and accu-racy in dose measurements, (ii) to improve our un-derstanding of the physics of the luminescence pro-cesses, and (iii) to extend the dose range.  A pulsed stimulation (POSL) and time resolved (TR) single photon counting facility has been devel-oped [1] to aid investigations in luminescence phys-ics, and for the separation of luminescence signals of interest from mixed signals with very different lumi-nescence lifetimes. The TR-POSL facility, with its high temporal resolution in data acquisition (< 1ns), together with the ability to use different stimulation wavelengths (from blue, green and IR LEDs) and temperatures, provides a powerful tool for investigat-ing the complexity of charge movement during OSL; this, for example, has been recently applied to feld-spar luminescence [2]. The standard POSL offers PMT gating in selectable stimulation off-periods thereby  providing a routine approach to maximising the signal-to-noise ratio (by suppressing the break-through), and to isolating the signal of choice from mixed samples. An dedicated program for analysis of TR-POSL data can present the data as 3D surface plots and post-process the data to provide standard OSL decay curves derived from up to 5 individually defined gating intervals. There is considerable demand for extending the age range of luminescence dating. An improved vio-let stimulation attachment has been developed to ac-cess deep traps in quartz [3] with extended dose re-sponse. This attachment includes a 405 nm laser di-ode delivering ~70 mW/cm2 to the sample position, and appropriate filtration of both the stimulation and the detection light. Typical breakthrough is ~500 cps with the sample held at 125°C. To access the extend-ed dose response of feldspars, an IR radio-fluorescence facility has been developed; others have argued that this method samples a stable, non-fading signal from K-feldspars [4]. A cooled red sensitive photomultiplier module (Hamamatsu H7421-50) is coupled through a light guide to the sample position under the beta irradiator. Analysis software has been developed for routine, automated dose measurements using a single-aliquot procedure [5]. A significant fraction of the dose absorbed by natural K-rich feldspar samples originates from inter-nal 40K. In the absence of routine concentration measurements, most dating studies assume an internal K content of 12%, based on stoichiometry. To test this assumption, and for routine use in luminescence dating, we have developed an X-ray fluorescence spectrometer attachment and an analytical method for major element analysis of quartz and feldspar sepa-rates; this results in a relative estimate of Na-, K-, Ca-feldspar and quartz from each sample disc. Several improvements have also been made to in-crease precision and accuracy of dose measurement during routine measurements. For example a simple method for characterising, quantifying and correcting any irradiation field non-uniformity has been devel-oped; this is especially important for reducing over-dispersion in single-grain dose estimates. Similarly, it is often deemed necessary to know the grain count and grain size distribution for each sample disc. A sample camera with built-in illumination is now available; this gives 5 Mpixel sample images for rou-tine image processing and documentation. Finally a correction method has been developed for bright samples that give count rates in the non-linear region of the PMT. Using this method the maximum usable count rate is increased from ~5 to ~40 Mcps.  References:  [1] Lapp, T., et al., 2009, Development of pulsed stimulation and Photon Timer attachments to the Risø TL/OSL, Reader, Radiat. Meas.44, 571-575 [2] Jain, M., Ankjærgaard. C., 2011, Towards a non-fading signal in feldspar: Insight into charge transport and tunnelling from time-resolved optically stimulat-ed luminescence, Radiat. Meas. 46, 292-309. [3] Jain, M., 2009, Extending the age range probing deep traps in quartz with 3.06 eV photons, Radiat. Meas. 44, 445-452. [4] Erfurt, G., Krbetschek, M.R., 2003, Studies on the physics of the infrared radioluminescence of po-tassium feldspar and on the methodology of its appli-cation to sediment dating, Radiat. Meas. 37, 505-510. [5] Buylaert, J.P et al., 2012, IR-RF dating of sand-sized K-feldspar extracts: a test of accuracy, Radiat. Meas. 47 (9), 759-765. 

Review of new facilities on a TL/OSL reader for retrospective dosimetry

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Review of new facilities on a TL/OSL reader for retrospective dosimetry

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