Birol Engin

Electron spin resonance age determination of a travertine sample from the southwestern part of Turkey

Abstract Travertine powdered samples collected from Denizli in the southwestern part of Turkey appear to be suitable for dating by ESR analysis due to presence of a g =2.0006 ESR signal. In general, ESR spectra of natural travertine show two absorption lines: g =2.0006 and g =2.0056. 60 Co gamma-ray irradiations enhance the g =2.0006 signal but not g =2.0056. The signal amplitude of the g =2.0056 line remains constant and shows no dose dependence after annealing at 150–180°C for periods from 15 min to 2 days. Line g =2.0056 disappears in turn after an annealing of 15 min at 400°C. Thermal annealing experiments at different temperatures for different annealing times show that the only travertine ESR signal stable enough for dating of ages over the past 10 Ma, is the one at g =2.0006. The present ESR dating result is 1.11±0.11 Ma. The g =2.0006 signal used for dating appears to correspond with the 280°C TL peak, but at elevated temperatures the mean life, accumulated dose and age of the latter is significantly less than that measured by post irradiation analysis using the ESR signal. This can be attributed to coming from other carbon-containing paramagnetic centers. In fact, gamma-ray absorbed dose rate dependence of the ESR signal has been studied, and no dependence was observed over a 12-fold change in dose rate.

Thermoluminescence dating of Denizli travertines from the southwestern part of Turkey

Abstract The experimental determination of the formation age of a travertine collected from Denizli region in the southwestern part of Turkey was investigated using the thermoluminescence(TL) method. The first glow peak of calcite crystals of travertine limestone observed at 280°C was closely fitted with second-order kinetics and used for the evaluation of the accumulated dose. From the derived values of the trapping parameters for this glow peak, a mean lifetime can be predicted for ambient temperature, and hence the low peak should be stable enough to be used for dating this travertine. The thermoluminescence dating result is 828 ± 93 ka.

Thermoluminescence and electron spin resonance properties of some travertines from Turkey

Abstract For the sake of dating certain calcite geological samples, the TL and ESR properties of travertines from Denizli (in the southwestern part of Turkey) were studied and the effects of pre-heating temperature and pre-heating time on the sensitivity of the samples to radiation evaluated. Heat treatment above 350°C increases the sensitivity of all radiation-induced TL peaks except the 330°C glow peak. Results of gamma-ray dose calibration in travertine (CaCO3 crystal of trigonal symmetry) indicate that the 180 and 280°C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280°C glow peaks reasonably well. The Mn2+ lines of the ESR spectra are used to investigate the thermal decomposition processes of travertine samples, showing very good agreement with those of thermogravimetry. Glow mechanisms of TL in travertine have also been studied using ESR analysis. The pre-heating and subsequent laboratory irradiation procedure is found to enhance the TL and ESR signals of CO33− and CO2− centres. An isochronal thermal anneal sequence experiment showed that 180 and 280°C peaks in travertines are correlated with CO33− and CO2− centres in the same way that the peak at 330°C is correlated with SO2− centres. A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements.

Detection of gamma irradiated fig seeds by analysing electron spin resonance.

Seeds of fig produced in Turkey were studied by electron spin resonance (ESR) technique for detection purposes. Unirradiated fig seeds (control) exhibited a weak ESR singlet at g=2.0052±0.0003 (native signal). Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Variation of ESR signal intensity of irradiated samples at room temperature with time in a long-term showed that free radicals responsible from the ESR spectrum of fig seeds were not stable but detectable after 80days. Annealing studies at five different temperatures were used to determine the kinetic behaviour and activation energy of the radiation-induced radicals in fig seeds. A study on microwave saturation characteristics and thermal behaviour of the ESR singlet (g=2.0052) in irradiated and unirradiated fig seed samples was also carried out by using ESR technique. These preliminary results indicate that microwave saturation characteristics of the ESR signal at room and low temperatures may be useful method to distinguish irradiated fig seeds from unirradiated ones.

Study of the thermoluminescence dosimetric properties of window glass

This paper presents the main thermoluminescence (TL) dosimetric characteristics of commercial Turkish transparent window glass. The structure of the glow curves, including the number of peaks, was found to be dose-dependent. A low-temperature glow peak that at 160 °C shifts to higher temperatures was also observed with increasing storage time at room temperature. This result suggests that this TL glow peak is actually made up of two or more overlapping peaks. These we have attributed to the glow peaks at lower temperatures, which decay faster than the ones at higher temperatures with storage time. The thermal fading of the window glass sample at room temperature showed a relatively sharp decay of about 60% occurring over a period of 28 days, after which the decay rate is small for a measured period of 250 days. In order to the improve the post-irradiation stability of the glow curve, the glass samples were heated after irradiation. To remove the unstable TL peaks responsible for the initial rapid fading, post-irradiation heating at 160 °C for 10 min was found to be the most suitable procedure. The dosimetric characteristics of the post-irradiation heated window glass examined in this study include fading, gamma photon dose-response, reproducibility, batch sensitivity, humidity influence, a dose-rate effect and photon energy response. Dose-response was found to be appropriate for dosimetry in the range 5 Gy to 10 kGy. The post-irradiation heating procedure did not affect the main dosimetric characteristics of the window glass samples. The results in this work suggest that the materials could, by using the TL technique, be a suitable candidate for alternative dose measurements in radiation processing, provided that a judicious choice of the post-irradiation heat temperature is made to minimize fading.

The use of ESR technique for assessment of heating temperatures of archaeological lentil samples.

Heat-induced paramagnetic centers in modern and archaeological lentils (Lens culinaris, Medik.) were studied by X-band (9.3GHz) electron spin resonance (ESR) technique. The modern red lentil samples were heated in an electrical furnace at increasing temperatures in the range 70-500 degrees C. The ESR spectral parameters (the intensity, g-value and peak-to-peak line width) of the heat-induced organic radicals were investigated for modern red lentil (Lens culinaris, Medik.) samples. The obtained ESR spectra indicate that the relative number of heat-induced paramagnetic species and peak-to-peak line widths depends on the temperature and heating time of the modern lentil. The g-values also depend on the heating temperature but not heating time. Heated modern red lentils produced a range of organic radicals with g-values from g=2.0062 to 2.0035. ESR signals of carbonised archaeological lentil samples from two archaeological deposits of the Van province in Turkey were studied and g-values, peak-to-peak line widths, intensities and elemental compositions were compared with those obtained for modern samples in order to assess at which temperature these archaeological lentils were heated in prehistoric sites. The maximum temperatures of the previous heating of carbonised UA5 and Y11 lentil seeds are as follows about 500 degrees C and above 500 degrees C, respectively.

Dose estimation, kinetics and dating of fossil marine mollusc shells from northwestern part of Turkey.

Electron spin resonance (ESR) spectroscopy was used to determine the geological formation age of fossil mollusc shells taken from marine terrace deposits (İkizlerçeşme-Çanakkale) in northwestern part of Turkey. This work reports the first results obtained by the ESR technique on shells collected from this region. In the ESR spectra of the natural and γ-irradiated shell samples, two different signals attributed to orthorombic (gxx=2.0030, gzz=2.0015, gyy=1.9980) and isotropic (g=2.0006) CO2(-) ion radicals were overlaped (Signal C). Annealing and kinetic experiments suggest the possibility of using the ESR signal at g=2.0015 (C signal) for the estimation of accumulated geological doses. The ESR signal growth curve on additional gamma irradiation has been best fitted by a combination of two single exponential saturation functions. This may support the existence of at least two components of the g=2.0015 ESR dating signal. Based on this model, the accumulated dose of the samples was determined as 110±11Gy. Also the isothermal decay curves of the ESR dating signal could be best described by the combination of two first order decay functions. Activation energy and meanlifetime values at 15°C of the two components were calculated as E1=1.4±0.1eV, E2=1.1±0.1eV, τ1=7.2×10(6) years and τ2=3.3×10(3) years, respectively. Uranium content of the studied shells was found to be high according to their chemical analysis. This may point out that the marine shell has received uranium from outside particularly in carbonate sediment. Therefore, the ESR age of the samples was also calculated using Early Uptake (EU), Linear Uptake (LU) and Combined Uptake (CU) models and results were discussed.

ESR and TL studies of irradiated Anatolian laurel leaf (Laurus nobilis L.)

Laurel leaf (Laurus nobilis L.) samples that originated from Turkey were analyzed by electron spin resonance (ESR) and thermoluminescence (TL) techniques before and after γ-irradiation. Unirradiated (control) laurel leaf samples exhibit a weak ESR singlet centered at g=2.0020. Besides this central signal were two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. The dose–response curve of the radiation-induced ESR signal at g=2.0187 (the left satellite signal) was found to be described well by a power function. Variation of the left satellite ESR signal intensity of irradiated samples at room temperature with time in a long term showed that cellulosic free radicals responsible for the ESR spectrum of laurel leaves were not stable but detectable even after 100 days. Annealing studies at four different temperatures were used to determine the kinetic behavior and activation energy of the radiation-induced cellulosic free radicals responsible from the left satellite signal (g=2.0187) in laurel leaves. TL measurements of the polymineral dust isolated from the laurel leaf samples allowed distinguishing between irradiated and unirradiated samples.

ESR dating of calcrete nodules from Bala, Ankara (Turkey): preliminary results.

The age of two calcrete nodules (C1 and C2) from the Bala section in the region of Ankara, Turkey, is determined by the Electron Spin Resonance (ESR) method. Three radiation-induced ESR signals at g=2.0056 (A signal), g=2.0006 (C signal) and g=2.0038 (broad signal, BL) were observed. The broad signal (BL) intensity was used as a dating signal. The properties of this dating signal are described in this manuscript. The calcrete nodules were irradiated with a (60)Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve and fitted well with the single exponential saturation functions. Based on this model, accumulated dose (D(E)) values for dating are obtained using the multiple-aliquot additive dose method. The D(E) values of C1 and C2 calcretes are 1880±207 and 671±67 Gy, respectively. The ESR ages of the two calcrete samples are obtained by assessing the annual dose rate (D) from the content of (238)U, (232)Th and K(2)O determined by wavelength dispersive X-ray fluorescence (XRF) spectrometry. The results are 761±120 and 419±64 ka, respectively, falling into the Middle Pleistocene Epoch in the geological time scale in agreement with the positions of the stratigraphical record.

ESR dating of stalagmite from Keloğlan cave in the southwestern part of Turkey

The determination of the geological age of two stalagmites (designated as A and B) found in Keloğlan cave (Denizli, Acıpayam, Turkey) was investigated using an electron spin resonance (ESR) technique. The natural ESR spectra had the signals of Mn2+ in addition to the signal at g=2.0006. In the ESR spectra of the γ-irradiated samples, three additional signals appear at g=2.0030, g=20016 and g=1.9972. The radicals produced by irradiation in stalagmites were attributed to orthorhombic and isotropic CO ion radicals. The signal intensity of the CO was used as a dating signal. Stalagmites were irradiated with a 60Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve, and fitted with the sum of two single exponential saturation functions. Based on this model, accumulated geological dose (DE) values for dating are obtained by using an additive dose method. The DE values of A and B stalagmites for each section range from 15±1 to 83±4 and 25±1 to 100±6 Gy, respectively. As the 238U, 232Th and 40K concentrations of the stalagmites are very low, the measured in situ value of the external gamma dose rate was used for dating calculations. Because some parts of the stalagmites show secondary calcite recrystallization in the pore spaces, the calculated age values of these parts do not agree with the model of stalagmite growth. Except these porous parts, the ESR ages of other sections between A.5–A.8 and B.3–B.6 range from 14±2 to 86±18 and 24±5 to 92±19 kyr, respectively, which is consistent with the model of stalagmite growth.