E. Bulur

An alternative technique for optically stimulated luminescence (OSL) experiment

An alternative technique is developed for observation of OSL by linearly increasing the intensity of the excitation source during readout. The technique allows the observation of OSL signals in the form of peaks unlike the decaying curves. The parameters of the new OSL peak can be used to obtain the intensity and the lifetime of the decay. With the technique it is also possible to discriminate overlapping OSL signals by using the peak positions.

Optically stimulated luminescence from quartz measured using the linear modulation technique

The optically stimulated luminescence (OSL) from heated natural quartz has been investigated using the linear modulation technique (LMT), in which the excitation light intensity is increased linearly during stimulation. In contrast to conventional stimulation, which usually produces a monotonically decreasing signal, linearly increasing the stimulation power gives peaks in the signal as a function of time. In cases where the OSL signal contains more than one component, the linear increase in power of the stimulation light may result in a curve containing overlapping peaks, where the most easily stimulated component occurs at a shorter time. This allows the separation of the overlapping OSL components, which are assumed to originate from different traps. The LM-OSL curve from quartz shows an initial peak followed by a broad one. Deconvolution using curve fitting has shown that the composite OSL curve from quartz can be approximated well by using a linear combination of first-order peaks. In addition to the three known components, i.e. fast, medium and slow components from continuous-wave-OSL studies, an additional slow component is also identified for the first time. The dose responses and thermal stabilities of the various components are also studied.

A simple transformation for converting CW-OSL curves to LM-OSL curves

Abstract A simple mathematical transformation is introduced to convert from OSL decay curves obtained in the conventional way to those obtained using a linear modulation technique based on a linear increase of the stimulation light intensity during OSL measurement. The validity of the transformation was tested by the IR-stimulated luminescence curves from feldspars, recorded using both the conventional and the linear modulation techniques. The transformation was further applied to green-light-stimulated OSL from K and Na feldspars.

Luminescence sensitivity changes in natural quartz induced by high temperature annealing: a high frequency EPR and OSL study

Quartz undergoes very significant luminescence sensitivity changes after high temperature annealing (0-1200 °C), with particular enhancement occurring between the phase transition temperatures 573 and 870 °C. In order to understand why this occurs, high frequency electron paramagnetic resonance (EPR), operating at 90 GHz, has been used to monitor the structure and population of defects in natural sedimentary quartz, following annealing and -irradiation. The results are compared with the optically stimulated luminescence (OSL) data of the same samples. It is shown that: (i) the structure and population of the dominant [AlO4 ]0 recombination centres are largely unaffected by the annealing process; (ii) the oxygen vacancy E´ centres are destroyed when annealed at temperatures between the phase transitions and; (iii) the numbers of both [TiO4 /H+ ]0 and [TiO4 /Li+ ]0 donors increase between 400 and 700 °C. Photo-EPR spectra are presented, providing evidence that both the Ti associated donors and Al acceptors are directly involved in the OSL process. The heat-induced changes in the population of these EPR defects is mirrored in part by the change in the luminescence sensitivity of several OSL components. Evidence is also presented suggesting that E´ may act as non-radiative centres competing in the OSL process.

LM-OSL from single grains of quartz: a preliminary study

Abstract The recently developed single grain attachment for the Riso TL-OSL reader has been modified to achieve linearly modulated optically stimulated luminescence (LM-OSL). Three different types of luminescence behaviour were observed in 81 quartz grains measured. These types are those showing only the easy-to-bleach component, those with only the hard-to-bleach component, and those exhibiting all components. The results of this preliminary study show that LM-OSL experiments carried out at the single grain level may give important insights into the luminescence properties observed when viewing samples consisting of multiple grains.

Infrared (IR) stimulated luminescence from feldspars with linearly increasing excitation light intensity

IR stimulated luminescence signal from potassium and sodium feldspars were studied by linearly increasing the excitation power from zero to a maximum value during the readout. The peak shaped signals observed in both feldspars could be approximated using a linear combination of three first-order components as deduced by curve fitting. The thermal and radiation dose dependent behavior of the IR-stimulated OSL curves were also studied.

An optical fiber radiation sensor for remote detection of radiological materials

This paper demonstrates the feasibility of a portable radiation sensor system that uses the pulsed optically stimulated luminescence technique to remotely interrogate an aluminum oxide (Al/sub 2/O/sub 3/:C) radiation sensor via an optical fiber. The objective is to develop a system for applications requiring simple and inexpensive sensors for widespread monitoring of ionizing radiation levels, which can be remotely interrogated at regular periods with little or no human intervention and are easy to install, operate, and maintain. Results on the optimization and performance of the system are presented. The current minimum detectable dose is of the order of 5 /spl mu/Gy, which is already satisfactory for applications such as the monitoring of radioactive plumes from radioactive waste sites. We also discuss potential developments that could decrease the minimum detectable dose to allow radiation doses as low as the background level to be measured over short time intervals, making the system more versatile for detecting radiological materials.

Thermoluminescence in gallium sulfide crystals: an unusual heating rate dependence

Trap centres in gallium sulfide single crystals have been investigated by thermoluminescence measurements in the temperature range of 10–230 K. A curve-fitting method was utilized to evaluate the activation energies (52, 200 and 304 meV) of the revealed three trap centres. The heating rate dependence and trap distribution of the peaks have been studied using experimental techniques based on various heating rates and various illumination temperatures, respectively. An anomalous heating rate dependence of the high-temperature peak was found by carrying out TL measurements with various heating rates between 0.2 and 1.0 K/s. This behaviour was explained on the basis of a semi-localized transition model. Whereas normal heating rate dependence was established for low-temperature peak, that is, the TL intensity of the glow curve decreases and the peak maximum temperature shifts to higher values with increasing the heating rate. Moreover, a quasi-continuous trap distribution with the increase of activation energies from 52 to 90 meV, from 200 to 268 meV and from 304 to 469 meV for the observed three different traps was established employing the various illumination temperatures method.

Plasma Generation in a Gas Discharge System With Irradiated Porous Zeolite

The influence of pressure [from atmospheric pressure (AP) to 10-2 torr] and β-radiation (1-kGy β doses) on the current-voltage characteristics, charge trapping effects in porous surfaces, and breakdown voltage (UB) in AP microplasmas are discussed for the first time. This is due to the zeolite cathode (ZC) exposure to β-radiation resulting in substantial decreases in the UB, discharge currents, and conductivity due to increase in porosity of the material. Results indicated the enhancement of plasma light intensity and electron emission from the ZC surface with the release of trapped electrons which are captured by the defect centers following β-irradiation. The porosity of the ZC and radiation defect centers has a significant influence on the electrical and optical properties of the devices manufactured on its base.

Thermoluminescence properties of Tl2Ga2S3Se layered single crystals

The trap center(s) in Tl2Ga2S3Se single crystals has been investigated from thermoluminescence (TL) measurements in the temperature range of 10–300 K. Curve fitting, initial rise, and peak shape methods were applied to observed TL glow curve to evaluate the activation energy, capture cross section, and attempt-to-escape frequency of the trap center. One trapping center has been revealed with activation energy of 16 meV. Moreover, the characteristics of trap distribution have been studied using an experimental technique based on different illumination temperature. An increase of activation energy from 16 to 58 meV was revealed for the applied illumination temperature range of 10–25 K.