Single Grain Luminescence Reader

In collaboration with Risø National Laboratory, Aberystwyth has developed the worlds first automated single grain luminescence reader.This system has been designed to enable measurements of the luminescence emitted by single sand-sized grains of sediment to be measured. The ability to make such measurements will provide exciting data on the fundamental processes involved in luminescence from quartz and feldspars, and provide a powerful tool in dating.

The first system that was built is housed in Risø (Denmark), while the only other such reader currently in use was purchased with an NERC JREI grant to Geoff Duller in 1999 and is housed here in the Aberystwyth luminescence laboratory.

How does the system work?

What does it look like?

What can it do?

What do the results look like?

What to do if you are interested in using the single grain reader?

Publications about single grain measurements

How does the system work?

The single grain system is designed as an 'add-on' to the automated luminescence reader produced at Risø National Laboratory, Denmark. This system provides a wide range of measurement possibilities, and the single grain attachment enhances these. The basic system incorporates a computer controlled sample changer, with up to 48 separate sample holders, alpha and beta sources, and a hotplate that can be used to hold the sample at any temperature from room temperature to 700°C.

The single grain system is based around a 10 mW solid state diode pumped laser emitting at 532 nm. The output from this laser is focussed to a spot approximately 50 µm in diameter. This beam can be directed at the sample held within the automated Risø luminescence reader on a 9mm diameter aluminium disc. A crucial feature of the single grain system is that the beam can be moved anywhere on the sample disc using two mirrors set at right angles to each other. These mirrors are computer controlled so that they can be positioned with a precision of better than a micrometre (one thousandth of a millimetre).

Standard luminescence measurements are made on samples that are mounted on plain aluminium discs. For the single grain reader it is important that the location of each grain is defined. Therefore an array of holes is drilled into the surface of the aluminium disc (either 9 by 9 holes or 10 by 10 holes).

Image of a single grain disc showing the array of sample holes and the three locating holes

A single grain disc with an array of 9 by 9 samples holes. Each sample hole is 300 microns in diameter and 300 microns deep. Around the edge of the disc you can see three larger holes that pass completely through the aluminium disc. These are locating holes that are used by the system to create a frame of reference. This then permits the software to calculate the position of each of the sample holes and point the laser at each grain.

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What does the system look like?

In normal use not much of the 'workings' of the single grain system are visible. This is because they are housed in a light tight box to prevent stray laboratory light from entering the measurement chamber. The photograph shown below was taken with the lid of the single grain attachment taken off. The most striking feature is the green laser beam. The laser itself is mounted on the right hand side of the image. It then passes through a series of three lenses in order to expand and then focus the beam. The two mirrors which are used to steer the beam can be seen on the right hand side of the image. The first mirror turns the beam through 90 degrees, while the second one is set at 22.5 degrees, so resulting in the beam passing down into the measurement chamber (shown at the top right of the image) at 45 degrees. This avoids distortion of the system in the final stage of the beam path. (Note that the photomultiplier tube that records the luminescence signal has been removed for this photograph. Normally it would stand immediately above the sample chamber).

View of the single grain attachement from above when it is mounted on a Risų reader

From this image it is difficult to see the rest of the Risø reader. The only part that is clearly visible is the beta source in the upper left hand corner of the image within its lead shielding. The photograph below shows the single grain system mounted on a Risø reader. The circular carousel on which the samples are mounted is shown, along with the photomultiplier tube. The laser beam can also be seen coming out of the base of the single grain reader. For the purposes of this photograph the lid of the reader has been left above its normal position.

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What can it do?

The system can measure optically stimulated luminescence from single grains placed in each of the 81 sample holes on a disc. Although the laser emits at a fairly long wavelength (532 nm) compared with some other stimulation sources currently used for OSL, and has a modest power (10 mW), the beam is focussed to a spot approximately 50 µm in diameter. Therefore the optical power density is high (something like 50 W.cm-2), approximately two to three orders of magnitude higher than normal OSL systems. The effect of this is that the OSL signal from a grain can be measured very rapidly, with the typical measurment time for quartz being one second.

IMAGE of a decay curve

A novel type of OSL proposed by Bulur (1996) is to linearly increase the intensity of the optical stimulation during the OSL measurement. Typically the intensity is ramped from zero to 100% of the full intensity and the resulting signal recorded. This is known as linearly modulated optically stimulated luminescence (LM-OSL). Recently the software on the single grain reader has been adapted so that this form of measurement can now be made on single grains. This is already providing exciting insights into luminescence processes and should be a fruitful avenue of research in the future.

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What do the results look like?


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What to do if you are interested in using the single grain reader?

Time on the single grain reader is heavily used by members of the luminescence laboratory, but I am always interested to hear from people who have suggestions for novel or interesting applications of the equipment. This might be measurement of a different type of material, or the application of the single grain procedure to important Quaternary dating issues.

To make any enquiries about the single grain reader please contact Geoff Duller:-

Institute of Geography and Earth Sciences
University of Wales
Aberystwyth
Ceredigion SY23 3DB

Fax:        +44-1970-622658
E-mail:    Geoff.Duller@aber.ac.uk

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Publications about single grain measurements

This list contains publications involving this laboratory on single grain equipment and measurements. A more complete list of papers relating to single grains will be produced in the future.

Publications specifically about the system developed by Aberystwyth and Risø

Bøtter-Jensen L., Duller G. A. T., and Murray A. S. (2000) Advances in luminescence measurement systems. Radiation Measurements 32, 523-528.

Duller G. A. T., Bøtter-Jensen L., Kohsiek P., and Murray A. S. (1999) A high-sensitivity optically stimulated luminescence scanning system for measurement of single sand-sized grains. Radiation Protection Dosimetry 84, 325-330.

Duller G. A. T., Bøtter-Jensen L., Murray A. S., and Truscott A. J. (1999) Single grain laser luminescence (SGLL) measurements using a novel automated reader. Nuclear Instruments and Methods: B 155, 506-514.
 

Publications dealing with single grain properties

Duller G. A. T. (2000) Dose distributions determined from measurements of single quartz grains. ISLA-2000, 78-85.

Duller G. A. T., Bøtter-Jensen L., and Murray A. S. (2000) Optical dating of single sand-sized grains of quartz: sources of variability. Radiation Measurements 32, 453-457.

Truscott A. J., Duller G. A. T., Bøtter-Jensen L., Murray A. S., and Wintle A. G. (2000) Reproducibility of optically stimulated luminescence measurements from single grains of Al2O3:C and annealed quartz. Radiation Measurements 32, 447-451.

Publications dealing with the application of single grains to Quaternary dating

Duller G. A. T. and Murray A. S. (2000) Luminescence dating of sediments using individual mineral grains. Geologos 5, 88-106.
 

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This page was last updated on the 4th of October 2000. Any comments or suggestions should be directed to Geoff Duller via e-mail at Geoff.Duller@aber.ac.uk