12 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 10 / 12
Yayın The correlation of fast OSL component with the TL peak at 325 degrees C in quartz of various origins(Elsevier Science BV, 2010-02) Kitis, George; Güneç Kıyak, Nafiye; Polymeris, George S.; Tsirliganis, Nestor C.The fast component of the optically stimulated luminescence (OSL) signal in quartz is the basic tool for the optical dating. Its relation with the thermoluminescence (TL) glow-peak at about 325 degrees C is well established for naturally irradiated quartz. This relationship is also an important part of a general model for quartz on which many theoretical simulations of various OSL experimental results have been based. In the present work this relationship is systematically investigated in nine quartz samples of different origin. The linearly modulated OSL (LM-OSL) curves of all quartz samples for stimulation time less than 50s consists of two components discriminated easily by a computerized curve deconvolution (CCD) analysis. By comparing the un-bleached to the respective bleached TL glow-curve, it is found that the system of these two fast OSL components is directly related with only a small portion of the electron traps responsible for the TL glow-peaks in the temperature region 200-400 degrees C. By increasing the stimulation times, besides the two fast components, the medium and the slow components are also obtained. The medium and slow components are clearly related with the main body of the electron traps responsible for TL glow-peaks in the same temperature region 200-400 degrees C. Despite their different origin all quartz samples show an appreciable homogeneity concerning the number and time position of the individual components, whereas, the relative TL/OSL intensities vary strongly from sample to sample with the integrated TL intensity being generally much less than the integrated OSL intensity.Yayın The firing temperature of pottery from ancient Mesopotamia, Turkey, using luminescence methods: a case study for different grain-size fractions(Wiley-Blackwell, 2014-10) Polymeris, George S.; Güneç Kıyak, Nafiye; Koul, Dileep K.; Kitis, GeorgeThe assessment of the firing temperature of a prehistoric pottery sample collected from ancient Mesopotamia, Turkey was studied using luminescence techniques. The methods for this estimation involved the observation of the thermal and pre-dose sensitization with various re-firing temperatures for both TL and the OSL signals. In the former case, the 110 degrees C TL peak and the rest of the glow curve were used as proxies in this study. In the framework of a first attempt to investigate the impact of grain-size dependence on the sensitization of the luminescence signals, the aforementioned study was performed with four different pottery grain-size fractions: (i) less than 60m, (ii) 60-90m, (iii) 90-180m and (iv) 180-250m. The results clearly demonstrated the firing temperature mark of approximate to 500 degrees C in for the grain size of 90-180m, whileas in the case of the lower grain-size fractiona third proxy, the ratio of the pre-dosed to the thermal sensitization, was seen to indicate the firing temperature. The remaining two grain-size fractions failed to provide any meaningful results with regard to the firing temperature estimation. The dependence of the TL characteristics on the grain size was explained in the framework of the mixed mineralogy.Yayın Thermoluminescence as a probe in bioactivity studies; the case of 58S sol-gel bioactive glass(IOP Publishing Ltd, 2011-10-05) Polymeris, George S.; Goudouri, Ourania Menti; Kontonasaki, Eleana; Paraskevopoulos, Konstantinos M.; Tsirliganis, Nestor C.; Kitis, GeorgeThe formation of a carbonated hydroxyapatite (HCAp) layer on the surface of bioactive materials is the main reaction that takes place upon their immersion in physiological fluids. To date, all techniques used for the identification of this HCAp formation are rather time consuming and not well suited to detailed and rapid monitoring of changes in the bioactivity response of the material. The aim of this work is to explore the possibility of using thermoluminescence (TL) for the discrimination between different bioactive responses in the case of the 58S bioactive glass. Results provided strong indications that the 110 degrees C TL peak of quartz can be used effectively in the study of the bioactive behaviour of 58S bioactive glass, since it is unambiguously present in all samples and does not require deconvolution analysis. Furthermore, the intensity of the 110 degrees C TL peak is proven to be very sensitive to the different bioactive responses, identifying the loss of silica which takes place at the first stages of the sequence. The discontinuities of the 110 degrees C TL peak intensity plot versus immersion time at 8 and 1440 min provide experimental indications regarding the timescale for both the beginning of amorphous CaP formation as well as the end of crystalline hydroxyl-apatite formation respectively, while the spike in the sensitization of the 110 degrees C TL peak, which was observed for immersion times ranging between 20 and 40 min, could be an experimental feature indicating the beginning of the crystalline HCAp formation.Yayın Thermally assisted OSL from deep traps in Al2O3:C(Pergamon-Elsevier Science Ltd, 2010-03) Polymeris, George S.; Raptis, Spyridoula; Afouxenidis, Dimitrios; Tsirliganis, Nestor C.; Kitis, GeorgeThe present work suggests an alternative experimental method in order to not only measure the signal of the deep traps in Al2O3:C without heating the sample to temperatures greater than 500 degrees C, but also use this signal for high dose level dosimetry purposes as well. This method consists of photo transfer OSL measurements performed at elevated temperatures using the blue LEDs (470 nm, FWHM 20 nm) housed at commercial Riso TL/OSL systems, after the sample was previously heated up to 500 degrees C in order to empty its main TL dosimetric trap. The influence of this procedure on specific features such as glow curve shape and sensitivity of the main TL glow peak was also studied.Yayın In-homogeneity in the pre-dose sensitization of the 110 degrees C TL peak in various quartz samples: The influence of annealing(Elsevier Science BV, 2012-03-01) Polymeris, George S.; Oniya, Ebenezer O.; Jibiri, Nnamdi N.; Tsirliganis, Nestor C.; Kitis, GeorgeThe pre-dose sensitization effect of the 110 degrees C TL glow-peak of quartz is a basic tool in thermoluminescence and optically stimulated luminescence dating and retrospective dosimetry. In the present work, a homogeneity study was performed on pre-dose sensitization in grains obtained from large quartz crystals samples collected from 10 different origins. The aliquot - to - aliquot scatter of the pre-dose sensitization of the 110 degrees C TL peak within each quartz crystal was monitored. The influence of the annealing on this scattering was also studied. Therefore, the investigation was applied to the un-fired "as is" samples as well as to samples annealed at 900 degrees C for 1 h following cooling to room temperature in air. The results showed that in the case of "as is" quartz the sensitization effect vary strongly within each aliquot of the same quartz sample. This strong variation is removed by both the high temperature annealing as well as heating up to 500 degrees C, involved in the TL measurements. These results are generally discussed in the framework of existing models and applications of the effect.Yayın Dissolution and subsequent re-crystallization as zeroing mechanism, thermal properties and component resolved dose response of salt (NaCl) for retrospective dosimetry(Pergamon-Elsevier Science Ltd, 2011-09) Polymeris, George S.; Kitis, George; Güneç Kıyak, Nafiye; Sfamba, Ioanna; Subedi, Bhagawan; Pagonis, VasilisIn the present study we report dosimetric properties of iodized salt aiming at using it as an accidental luminescent dosimeter. It was found that the very good sensitivity of its main dosimetric peak is strongly affected by thermal treatments. This is also the case for OSL emission. The sensitivity loss due to heating implies that caution should be exercised while applying single aliquot protocols for dose evaluation. The sequence of dissolution and subsequent re-crystallization was established to be an extremely effective zeroing mechanism for the TL signal. The linearity in the dose response was also monitored in the case of dissolved and subsequently re-crystallized salt. In the case of naturally occurring salt, zeroing of the TL signal due to dissolution as well as the linearity of dose response up to doses as large as 100 Gy were found to be very promising features for dating applications.Yayın Reconstruction of thermally quenched glow curves in quartz(Pergamon-Elsevier Science Ltd, 2012-04) Subedi, Bhagawan; Polymeris, George S.; Tsirliganis, Nestor C.; Pagonis, Vasilis; Kitis, GeorgeThe experimentally measured thermoluminescence (TL) glow curves of quartz samples are influenced by the presence of the thermal quenching effect, which involves a variation of the luminescence efficiency as a function of temperature. The real shape of the thermally unquenched TL glow curves is completely unknown. In the present work an attempt is made to reconstruct these unquenched glow curves from the quenched experimental data, and for two different types of quartz samples. The reconstruction is based on the values of the thermal quenching parameter W (activation energy) and C (a dimensionless constant), which are known from recent experimental work on these two samples. A computerized glow-curve deconvolution (CGCD) analysis was performed twice for both the reconstructed and the experimental TL glow curves. Special attention was paid to check for consistency between the results of these two independent CGCD analyses. The investigation showed that the reconstruction attempt was successful, and it is concluded that the analysis of reconstructed TL glow curves can provide improved values of the kinetic parameters E, s for the glow peaks of quartz. This also leads to a better evaluation of the half-lives of electron trapping levels used for dosimetry and luminescence dating.Yayın TL/OSL properties of crystalline inclusions from heavy, barytes loaded, concrete(Pergamon-Elsevier Science Ltd, 2010-03) Güneç Kıyak, Nafiye; Polymeris, George S.; Kitis, GeorgeIn the present work, we report the luminescence data obtained from heavy, barytes loaded, concrete containing many crystalline inclusions, extracted from a shielding block located at CERN. The use of both Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals, resulting from a specific trap at about 200 degrees C, is investigated for retrospective dosimetry purposes. By applying thermal cleaning experiments the TL signal of interest was isolated. Basic TL and OSL properties as thermal and optical stability, repeatability and mainly the linearity of the TL and OSL signals as a function of beta dose were investigated. The implications of all these luminescence properties to retrospective dosimetry are also briefly discussed.Yayın Thermoluminescence and optically stimulated luminescence properties of natural barytes(Elsevier Ltd, 2010-12) Kitis, George; Güneç Kıyak, Nafiye; Polymeris, George S.Heavy, baryte-loaded, concrete is commonly used as radiation shielding material around high energy particle accelerators. Concrete samples received from a shielding block located at CERN cite contain many crystalline inclusions which were identified as barytes by X-ray diffraction analysis and separated by their color, classified as white, orange and green. Basic properties of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals of these barytes samples such as thermal and optical stability, repeatability and mainly the linearity of both their luminescence responses were investigated as a function of beta dose These results are also discussed regarding detailed investigation on the correlation between TL and OSL signals and their implications for retrospective dosimetryYayın Investigation of OSL signals from very deep traps in unfired and fired quartz samples(Elsevier Science BV, 2010-03-15) Kitis, George; Güneç Kıyak, Nafiye; Polymeris, George S.; Pagonis, VasilisThis paper presents an attempt to isolate experimentally optically stimulated luminescence (OSL) signals which may originate from very deep traps (VDT) in quartz samples. As VDT we consider those traps which are responsible for TL glow peaks with a peak maximum temperature above a TL readout temperature of 500 C. The basic experimental procedure used to isolate OSL signals from VDT is heating the quartz samples to 500 C immediately before measuring the OSL signal. The study was carried out on eight quartz samples of very different origins; it is found that all eight samples exhibit OSL signals from VDT, and for a wide region of OSL stimulation temperatures. The OSL signal from VDT depends strongly on the type of quartz sample studied and on whether the sample was fired at high temperatures or not. The behavior of the OSL signal from VDT as a function of the stimulation temperature is found to be very different in fired and unfired samples. The thermal activation energy E for the OSL signals from VDT is obtained in both fired and unfired samples. The OSL signal from VDT in quartz samples fired at 800 C for 1 h is very high, and the OSL curves consist of three well-defined components and a fourth slow component which is rather poorly resolved. The dose response of these components is obtained using a computerized deconvolution procedure for the dose region 0.5-300 Gy. The results are of importance for dating of ancient fired ceramics, since OSL signals from VDT could potentially extend appreciably the equivalent dose region toward both lower and higher values.
