Canan Aydaş

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.

Identification of irradiated foodstuffs using ESR microwave saturation

This study aims primarily to investigate the usage of differences in microwave (MW) saturation behaviour of food samples for identification of radiation treatment. Twenty different samples (dry plant, herbal, spice etc.) which do not have radiation specific satellite ESR signal were especially selected. It is not possible to detect radiation treatment on these samples by European standard (EN 1787, 2000). MW saturation studies were performed on all samples in the range of 0.01-160mW. Our experimental results demonstrate that radiation identification can be possible for ten samples and cannot be possible for the other ten samples by performing the MW saturation studies.

The use of ESR spectroscopy for the identification and dose assessment of irradiated pink shrimp (Parapenaeus longirostris) from Turkey

Turkish pink shrimp (Parapenaeus longirostris) samples were studied by electron spin resonance (ESR) spectroscopy for identification and dose assessment purposes. In this work, the calcified shells of shrimps were used as a sample material. Before irradiation, all shrimp shell samples exhibit one weak ESR singlet with a g-factor of 2.0047. After irradiation, all samples exhibit two asymmetric ESR signal components centered at g-values of 2.0013 and 1.9959. The dose–response curves of the samples exposed to gamma radiations were found to be described well by a single saturation exponential function. Variation of ESR signal intensity of irradiated samples at room and−20 °C temperatures with time in a long-term showed that free radicals responsible from the ESR spectrum of shrimp shells were not stable but still detectable after 87 days. Also, the kinetic behavior of signal at g=2.0013 was studied and the additive dose method was used to evaluate the dose in the product.

An investigation of the dosimetric and kinetic properties of sand using ESR and TL techniques.

In this research, the general dosimetric and kinetic properties of sand from a beach in southern Turkey were investigated using electron spin resonance (ESR) and thermoluminescence (TL) techniques. The ESR dose response curve presents linear behaviour in the dose range of 250-1000 Gy followed by sublinear behaviour in the dose range of 2-8 kGy. Kinetic behaviors and activation energy of the free radical were also calculated using the data obtained from annealing studies performed at four different temperatures (220, 240, 260 and 280°C). The activation energy value was calculated as 1.47 eV. The long-term fading of the ESR signal at room temperature turned out to be best described by a second-order kinetic decay function. The presence of measurable ESR signal intensity even after a storage period of 90 days was considered as providing an opportunity in the dose estimation of irradiated sand sample. Although the TL glow curve of the natural (unirradiated) sand sample only has a single broad peak at 317°C, the glow curve of the irradiated sample has four glow peaks located at ~115°C, ~156°C, ~231°C and ~308°C and their intensity tends to be increased with absorbed dose.Tmax-Tstop and glow curve fitting results showed that presence of at least five peaks located at ∼116°C, 149°C, 228°C, 306°C and 360°C. This result suggests that the apparently single glow peak D may consist of two or more overlapping glow peaks. According to the thermal fading of the sand sample at room temperature, the TL signal intensities (23°C and 308°C) were found to be quite large after 30 days of storage this allows a more accurate measurement of the glow peak intensity. The additive dose method, variable heating rate method (VHRM), Tmax-Tstop and glow curve fitting method were used to number of peaks, dosimetric properties and kinetic parameters. This study shows that ESR and TL techniques could be successfully used to investigate the kinetics and dosimetric properties of sand sample. Furthermore, the results in this study plus the previous work done by the authors suggest that sand could, by using the ESR and TL techniques, be a suitable material for alternative dose measurement.