The Risø TL/OSL Reader Model DA-20 consists of:
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Automated 48-position sample changer system built into a vacuum chamber (lowest pressure < 0.2 mbar).
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Two exchangeable sample holders (each designed to hold 48 samples) for 9.7 mm diam. flat sample discs or 11.65 mm diam. sample cups.
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Vacuum sensing system with automated switching on reaching desired pressure, vacuum gauge, and combined vacuum/nitrogen solenoid valves (exclusive vacuum pump).
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Lift mechanism for heater element.
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Shaped Kanthal heater strip, endpoint temperature: 700°C.
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Filter holder to allow fitting of different optical detection filters.
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Photomultiplier housing with dynode chain and m-metal shielding.
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100 11.65 mm diameter stainless steel sample cups and 100 9.7 mm diameter flat stainless steel discs
Electronics, detectors and controls
The Risø TL/OSL Controller allows for flexible control of the TL/OSL system including input/output ports, counters, and heat profile generator.
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Continuous full sine wave programmable heating system that can perform a linear heating profile for TL, preheat, and isothermal functions (endpoint: 700°C).
- Automated software-based function control for activating beta irradiator, atmosphere valves and all mechanical movements.
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Single photon counting amplifier / discriminator system.
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Stabilised, adjustable high-voltage supply for PM tube (max. 1500 V).
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Linear, up to 40 x106 counts per second and low dark count EMI 9235QB15 PM tube.
Beta Irradiator attachment
The irradiator normally accommodates a 1.48 GBq (40 mCi) 90Sr/90Y beta source, which emits beta particles with a maximum energy of 2.27 MeV. The dose rate in quartz at the sample position is approximately 0.1 Gy/s. The detachable on-plate automated beta irradiator including beryllium foil vacuum interface provides software-controlled in-situ irradiations of samples
Infrared/Blue Light Optically Stimulated Luminescence (OSL) head
Optical stimulation is achieved using an array of light emitting diodes (LEDs), which are compact, fast and enables electronic control of the illumination power density. The standard system incorporates CW as well as LM-OSL stimulation. The array of LEDs is equipped with an optical feedback servo-system to ensure the stability of the stimulation power.
The key component for this process is the combined Infrared/Blue Light stimulated luminescence (IRSL/OSL) unit attachable to the Risø TL sample changer for IRSL/OSL measurements of a variety of natural and artificial materials.
The OSL unit is based on illumination with
1) clusters of 870 nm IR LEDs providing > 135 mW/cm2 at the sample and
2) clusters of 470 nm blue LEDs delivering > 80 mW/cm2 at sample.
The OSL unit enables flexible and combined BLSL/IRSL/TL measurements in automated sequences. The OSL/IRSL system includes a software controlled power supply to allow illumination power to be varied during a measurement sequence (e.g. for normalisation) or to ramp of the illumination power during an OSL readout to perform linearly modulated OSL (LM-OSL) to investigate trap distributions and OSL decay rate components.
Heating system
The heating element is based around a Kanthal heater strip, which is specifically shaped to match sample discs/cups supplied with the instrument. The sample holder can be placed over the heater plate by an automated sequence and heated to the desired temperature, between room temperature and 700°C, using a user defined heating rate. The reader chamber can be evacuated and subsequently refilled/circulated with different gas(es) at adjustable flow rates for elevated temperature measurements.
Software
Sequence Editor
The Sequence Editor is a flexible MS Windows software that permits the easy creation of any desired automated TL/OSL measurement sequence. These sequences can include any or all operations (e.g. preheat, irradiation, OSL, etc.) individually, or in combination.
The software allows for a large number of operations to be controlled in one measurement sequence. The user may also program the reader operations using a Macro language.
Sequences can be stored and recalled for future measurement routines. Live display of TL and OSL signals on the computer screen during a sequence run is provided. Data is stored in a format accessible by Viewer and Analyst (also provided).
Control program
The Control program allows the individual units of the reader to be tested. It is mainly used for test, adjustment and maintenance purposes.
Viewer
The Viewer is used to display and print curves, perform integration and export data from the data files.
Analyst
Analyst is a program designed to view, edit and analyse luminescence data collected using the Risø TL/OSL reader. It allows data to be exported in a variety of formats so that it can be transferred to other programs.
Analyst is especially developed for the Risø TL/OSL system by Prof. G.A.T. Duller, University College of Wales, Aberystwyth, UK.
Optical filters
The intensity of the stimulation light is approximately 10-18 orders of magnitude larger than the emitted
luminescence. In order to be able to measure the emitted luminescence, detection filters must be
used to prevent scattered stimulation light from reaching the PMT, and the spectral stimulation and
detection windows must be well separated.
The TL/OSL reader is per default supplied with a set of the following stimulation and detection filters cut to fit the filter holders:
• 7.5 mm Hoya U-340
• 2 mm Schott BG-39
• 3 mm Schott BG-3