In contrast to the detailed investigations on the dosimetric electron trap in feldspar only little has been done to understand the luminescence centers. We use a comparison of multiple spectroscopic techniques, site selective photoluminescence spectroscopy and time resolved measurements to further our understanding of the luminescence mechanisms and recombination sites, in a sample of Na rich plagioclase feldspar (oligoclase). Both the UV and violet–blue emissions show resonant excitations arising from a distribution of energy levels. We propose, contrary to the general understanding, that the green emission may not arise from Mn2+ in our sample and that photoionisation of this centre may be possible by excitation to the band tail states. The deep red emission is tied to the Fe3+, and the exponential rise in the UV excitation efficiency of this centre is discussed in the context of the band-tail model.

Here we compare the performance of an EMCCD-based imaging system with the standard laser-based single-grain Riso attachment. We first compare gamma dose distributions and the relative sensitivity of the two instruments is investigated using a single sample, by comparing the number of grains accepted into a dose distribution. EMCCD cross-talk is shown to be of concern at low light levels. We also make use of the fact that the EMCCD can observe TL signals from individual grains to examine the use of the correlation between the quartz 110 degrees C TL peak and the fast component OSL signal to correct for sensitivity change. Finally, we present the OSL dose distributions from a set of both well-bleached and poorly-bleached sedimentary samples. From a comparison of the measured doses, we conclude that the two instruments give indistinguishable dose estimates and dispersions, despite the fact that the laser-based system is effectively about four times as sensitive as the EMCCD. (C) 2015 Elsevier Ltd. All rights reserved.

A new automated Detection And Stimulation Head (DASH) has been developed for the Riso TL/OSL luminescence reader to provide easy access to new technologies, new signals and new measurement methods. The automated DASH includes a filter changer and a detector changer that makes it possible to change stimulation filters (4 x 4 filter combinations possible) and detectors (3 detectors possible) as part of a measurements sequence. The new automated DASH with dedicated driver electronics does not affect the use of other attachments, and can be retrospectively fitted to existing Rise TL/OSL readers. (C) 2015 Elsevier Ltd. All rights reserved.

We extend the localised transition model based on randomly varying recombination distances (Jain et al., 2012) to include Arrhenius analysis and truncated nearest neighbour distributions. The model makes important predictions regarding a) the physical understanding of the linear intercepts in the Arrhenius analysis for localised recombination systems and b) the relationship between charge depletion and shape of the luminescence decay curves; these predictions are successfully tested by experimental investigations. We demonstrate that this model successfully describes the kinetic behaviour, both thermal and optical, of the infrared stimulated luminescence signal from feldspar.Based on the application of this model, it is concluded that different infra-red stimulated luminescence emissions (UV, blue, yellow and far-red) follow the same kinetics, and, therefore, involve participation of the same electron (dosimetric) trap. The differences in thermal stabilities of the different emissions results from differences in number densities of the recombination sites. The results have implications for understanding the mechanism of the far-red emission, and the spatial distributions of recombination sites in feldspar. (C) 2015 Elsevier Ltd. All rights reserved.

In optically stimulated luminescence (OSL) dating and other retrospective dosimetry studies there is considerable demand for the ability to measure luminescence from individual dosimeters in the size range 50–500 μm diameter, either as separate grains or as part of a matrix. This work tests the potential of an electron multiplying charge-coupled device (EMCCD), providing extremely low level light detection. We characterize the performance of the device by discussing reproducibility and evaluating uncertainties in OSL signals. Finally we derive a typical single grain natural dose distribution with associated uncertainties.

In optically stimulated luminescence (OSL) dating and other retrospective dosimetry studies there is a considerable demand for the ability to measure luminescence from dosimeters in the size range 50-500 µm diameter, either as loose grains or as part of a matrix. In the past this has been achieved by stimulating each grain sequentially, and collecting all the luminescence using a PM tube. The alternative approach discussed here is to stimulate all the grains simultaneously and image the resulting luminescence. The potential of such OSL imaging systems has been investigated before although none have managed to break through into routine application. Here we describe a high sensitivity imaging attachment to the Risø TL/OSL platform. Images are captured by a Peltier cooled (-80 o C) Evolve EMCCD camera (Photometrics); this uses frame transfer and electron multiplier gain (up to 1000 times). The optics are based on fused silica lenses with anti-reflection coatings, providing high UV-VIS transparency, large numerical aperture (~0.35) and ~0.8 magnification. Because the focal plane is dependent on the emission wavelength, the optics are mounted on a sequence-controlled motorized focusing unit. Alternatively, near-UV achromatic optics are available, but at the cost of a lower UV sensitivity. Standard 9.7 mm diameter single grain discs (each containing 100 grain holes) are used to present the samples to the camera. Images collected during a single TL/OSL measurement are processed automatically to produce a TL glow curve or OSL decay curve summed over each grain location. Each disc is spatially located after each TL or OSL measurement to compensate for rotation and/or

This presentation summarises recent major improvements 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 accuracy in dose measurements, (ii) to improve our un-derstanding of the physics of the luminescence pro-cesses, and (iii) to extend the dose range.

In this paper we use a recently developed radioluminescence (RL) attachment to the Riso TL/OSL reader to test the InfraRed-RadioFluorescence (IR-RF) dating method applied to K-feldspar rich extracts from our known-age archive samples. We present experiments to characterise the instrument performance and to test the reproducibility of IR-RF measurements. These experiments illustrate the high sensitivity and dose rate of our RL system, the negligible influence of the turntable movement on IR-RF signals and the effectiveness of the built in 395 nm LED at bleaching IR-RF signals. We measure IR-RF ages on a set of samples with independent age control using a robust analytical method, which is able to detect any possible sensitivity change. Our IR-RF ages do not agree well with the independent age control; the ages of the younger samples (20-45 ka) are significantly over-estimated while the ages of the older samples (similar to 130 ka) are significantly under-estimated. Experiments are undertaken to investigate this disagreement and our results indicate that they can most likely be explained by 1) the difficulty of defining the correct bleaching level prior to regeneration measurements, 2) signal instability, 3) sensitivity changes between the additive dose and regenerative dose measurements, or a combination of these three factors. (C) 2012 Elsevier Ltd. All rights reserved.

This paper gives a review of recent developments in luminescence measurement facilities on the Riso TL/OSL reader including radio-luminescence (RL), exo-electron and violet stimulation attachments, and a method for characterising and if necessary correcting for beta irradiation source non-uniformity.We first describe improvements to the existing RL option to allow near infra-red detection (NIR) during irradiation by the built-in Sr-90/Y-90 beta source. The RL optical signal is collected by a liquid light guide through an F34-901 interference filter and detection is based on a dedicated thermoelectrically cooled NIR sensitive PMT (detection window peak at 855 nm, FWHM 27 nm). Software and electronics have been modified to allow standard TL and OSL measurements in the same sequence as RL measurements. Together with a new bleaching source based on a high-power UV LED (395 nm; 700 mW/cm(2)), this facility has been used to measure natural doses in feldspar using the decaying NIR RL signal.Secondly, we present a method for mapping radiation field of the built-in Sr-90/Y-90 beta-source and estimating grain-location specific dose-rates. This is important for the accuracy of single grain results, when radiation field is spatially non-uniform across the sample area. We document the effect of this correction method and further investigate on the effect of lifting the source to achieve a better dose-rate uniformity.Finally we summarise two recently-developed novel facilities to help investigate (i) the time scales involved in OSL processes (time-resolved exo-electron detection) and (ii) extending the age range (violet stimulated signals from deep quartz OSL traps). (C) 2012 Elsevier Ltd. All rights reserved.

We describe a portable luminescence reader suitable for use in remote localities in the field. The instrument weighs about 8 kg and is based around a 30 mm bialkali photomultiplier detecting signals through a glass filter centered on 340 nm. Stimulation is by 470 nm blue LEDs (24W in total) operating in both continuous wave and pulsed mode; photon counting can be gated such that it is active only during the pulse off-period. There are also two bleaching light sources (470 nm, 5W and 940 nm, 3 W), and the luminescence signals can be regenerated using a cold-cathode 30 kV X-ray tube, delivering similar to 0.06 Gy.s(-1). The three position sampling device has a heating element under each sampling position, able to heat the sample at 3 degrees C.s(-1) up to at least 250 degrees C. The sampler can be inserted into unconsolidated sediments, and is designed to prevent exposure of the mineral grains to ambient light during sampling. The performance of the instrument in terms of sensitivity and reproducibility is comparable to that of the standard bench-top laboratory TL/OSL Rise reader.We show that the portable luminescence reader is able to measure accurately an similar to 20 Gy quartz burial dose in a natural (unpretreated, no mineral separation) sandy sediment. We also show that, because of the configuration of the measurement head, the portable reader can be used to measure radioluminescence at elevated temperature in the presence of stimulation light; this facility is not available on conventional bench-top instruments. It is concluded that the portable luminescence reader can be used to accurately determine the quartz burial dose in loose sandy sediments in the field, without sample preparation or darkroom facilities. (C) 2011 Elsevier B.V. All rights reserved.

A time-resolved optically stimulated exo-electron (TR-OSE) measurement system has been developed using a Photon Timer attached to a gas-flow semi-proportional pancake electron detector within a Risø TL/OSL reader. The decay rate of the exo-electron emission after the stimulation pulse depends on the probability of (1) escape of electrons into the detector gas from the conduction band by overcoming the work function of the material and (2) thermalization of electrons in the conduction band, and subsequent re-trapping/recombination. Thus, we expect the exo-electron signal to reflect the instantaneous electron concentration in the conduction band. In this study, TR-OSE and time-resolved optically stimulated luminescence (TR-OSL) were measured for the first time using quartz, K-feldspar and NaCl by stimulating the samples using pulsed blue LEDs at different temperatures between 50 and 250 °C after beta irradiation and preheating to 280 °C. The majority of TR-OSE signals from all the samples decayed much faster than TR-OSL signals irrespective of the stimulation temperatures. This suggests that the lifetime of OSL in these dosimeters arises mainly from the relaxation of an excited state of the recombination centre, rather than from residence time of an electron in the conduction band.

The purpose of this paper is to investigate characteristics of luminescence signals resulting from pulsed optical stimulation of feldspars and thereby to understand the underlying processes giving rise to the signal. Fourteen different feldspar specimens were investigated using time-resolved optically stimulated luminescence (TR-OSL), and these signals can be mathematically described as a sum of 4 exponential components (a, b, c, d). The slowest component, d, increases with the duration of the light pulse as expected from the exponential model. The stimulation temperature dependence experiment suggests that the TR-OSL signal decay is governed by the recombination process and not by the excited state lifetime. Furthermore data from the TR-OSL signal dependence on stimulation time and preheat temperature suggest that the recombination process may not be a sum of exponentials, although the model cannot be rejected definitively.