Browsing by Author "Akça, S"

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    Characterization and thermoluminescence behavior of beta irradiated NaBaBO3 phosphor synthesized by combustion method
    Oglakci, M; Akça, S; Halefoglu, YZ; Dogan, T; Ayvacikli, M; Karabulut, Y; Topaksu, M; Can, N
    NaBaBO3 host material was synthesized using the combustion method. In order to optimize the performance of the material, effects of sintering temperatures varying from 600 degrees to 1000 degrees C were investigated. The sintering temperature and dwell time were found to have pronounced effects on the pure NaBaBO3 material. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to confirm the phase formation and examine the surface morphology of the prepared powder material, respectively. TL behavior of NaBaBO3 was studied at various beta doses. It is seen that the sample exhibits well resolved TL glow peak at a peak temperature about 175 degrees C and corresponding TL intensity increases with the increasing beta dose. However, TL glow peak slightly shifts to lower temperature with the increasing beta dose level. This is the first TL report of a phosphor with a NaBaBO3 host. The TL kinetic parameters were estimated by the peak shape (PS) method and CGCD software. TL glow curves of NaBaBO3 consist of several traps and exhibited second order kinetics. A possible TL mechanism was also discussed using the energy level model. The obtained results can provide valuable knowledge related to the investigation of the intrinsic nature characteristics of NaBaBO3 in research fields pertaining to dosimetry.
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    Comparative studies on thermoluminescence characteristics of non-doped Mg2SiO4 prepared via a solid-state reaction technique and wet-chemical method: An unusual heating rate dependence
    Dogan, T; Akça, S; Yüksel, M; Kucuk, N; Ayvacikli, M; Karabulut, Y; Canimoglu, A; Topaksu, M; Can, N
    Magnesium orthosilicate (Mg2SiO4) was synthesized via a traditional solid-state reaction and a wet chemical route. This study primarily reported the thermoluminescence (TL) behavior of Mg2SiO4 host. X-ray diffraction pattern revealed that Mg2SiO4 exhibits orthorhombic structure matched with JCPDS card 900-6398. Dose response, reproducibility and trap parameters of TL glow curves were evaluated to clearly reveal TL features. Two TL glow peaks situated at 81 degrees C and 192 degrees C were monitored at a heating rate of 2 degrees Cs-1. We observed anomalous heating rate effect for the peak centered at 192 degrees C whilst TL intensity of the peak at 81 degrees C decreases with elevating heating rate. Trap depths of the electrons within the trap centers were found to be 1.04 +/- 0.01eV and 1.37 +/- 0.01eV for both methods using peak shape (PS) method. Distribution of trap centers was examined using the T-max - T-stop method and this case indicated that the glow curves consist of single TL peaks. The intensity of TL glow curves exhibited a good linear dose response under total area up to 20 Gy. A comparison of the two preparation techniques revealed that TL characteristics of this phosphor are partly dependent and Mg2SiO4 could be a promising material for dosimetric application. (C) 2019 Elsevier B.V. All rights reserved.
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    Thermoluminescence properties of Tb doped Mg2SiO4 after beta irradiation
    Akça, S; Portakal, ZG; Dogan, T; Kucuk, N; Canimoglu, A; Topaksu, M; Can, N
    In this study, we performed Thermoluminescence (TL) experiments to extract the trapping parameters and dosimetric properties of Tb-doped Mg2SiO4 phosphors. Glow peaks located at 193, 270, and 350 degrees C were observed in the glow curve but the peak at 193 degrees C was especially investigated as a dosimetric peak in this study. We also observed an anomalous heating rate effect in which the maximum TL intensity of the glow curve augmented with an increasing heating rate. The computerized glow curve deconvolution (CGCD) method, initial rise (IR) and Hoogenstraaten's method were used to determine the activation energies of associated trapping centers for both BSL-TL 365 nm and IRSL-TL wideband blue filters. The TL characteristics of this phosphor indicate that Mg2SiO4:Tb3+ could be a promising material for dosimetric applications. Efforts should be made to improve the fading behaviour by adding other activators as co-dopants.
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    Thermoluminescence of Ce and Nd co-doped CaF2 phosphors after beta irradiation
    Yazan, H; Portakal-Uçar, ZG; Akça, S; Topaksu, M; Townsend, PD; Can, N
    In this study, we have synthesized CaF2:Nd3+,Ce3+ phosphors by solid state reaction method. The thermoluminescence (TL) properties of the family of synthesized phosphors (CaF2:Ce3+ and CaF2:Ce3+,Nd3+) were investigated using a combination of a SCHOTT BG39 and HC414/46 filters. This gave the highest TL intensity of each phosphor after 10 Gy beta-irradiation. Two TL glow peaks of CaF2:Nd3+,Ce3+ phosphor are centered at around 90 and 265 degrees C (with a heating rate of 2 degrees Cs-1). The glow peaks displayed a linear dose response in the range of 0.1-50 Gy. Various heating rates (VHR) were performed between 0.5 and 10 degrees Cs-1. It was seen that the TL intensity at 90 degrees C decreases and peak maximum temperature shifts to higher temperatures with an increasing heating rate. The TL intensity of the glow peak located at 265 degrees C increases with heating rate. The initial rise (IR) applied after T-M-T-stop experiment and computerized glow curve deconvolution (CGCD) methods in addition to the VHR method on the glow curves of CaF2:Nd3+,Ce3+ phosphor were used to determine the number of peaks, the order of kinetics (b), activation energy (E) and frequency factor (s). The response of TL glow curves remained constant within +2% deviation from the initial value after 10 cycles of reuse.
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    Luminescence studies of zinc borates activated with different concentrations of Ce and La under x-ray and electron excitation
    Küçük, N; Ayvacikli, M; Akça, S; Yüksel, M; Guinea, JG; Karabulut, Y; Canimoglu, A; Topaksu, M; Can, N
    Several ZnB2O4 powder samples having dopants concentrations of 0.1, 0.01, 0.04 wt% Ce and La were prepared using the nitric acid method via the starting oxides. Several complementary methods such as powder X-ray diffraction (XRD), thermal analyses environmental scanning electron microscopy (ESEM), Radioluminescence (RL) and Cathodoluminescence (CL) techniques were used. Unique luminescence properties of Ce doped ZnB2O4 powder samples are reported for the first time. A new luminescence bands appearing in red part of the spectrum and having all the characteristics of Ce3+ were obtained from RL results. Changing the Ce and La concentration of 0.01-0.1 wt% leads to an increase in RL and CL intensities of Ce3+ and La3+ ions and also CL emission spectra of ZnB2O4 show gradual shift towards longer wavelength. When we compare the luminescence intensity of the samples it is seen that Ce doped ZnB2O4 has the highest intense whereas La doped ZnB2O4 has the lowest one. However, emission spectra of both Ce and La doped samples kept unchanged.
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    Thermoluminescence behavior of Sm3+ activated ZnB2O4 phosphors synthesized using low temperature chemical synthesis method
    Bulcar, K; Dogan, T; Akça, S; Yüksel, M; Ayvacikli, M; Karabulut, Y; Kucuk, N; Canimoglu, A; Can, N; Topaksu, M
    This study is mainly centered on thermoluminescence (TL) behavior under beta excitation at room temperature (RT) of Sm3+ activated ZnB2O4 phosphors synthesized by low temperature chemical synthesis method. The prepared phosphors were characterized by the X-ray powder diffraction (XRD) method. The effects of dopant concentration, beta radiation dose (0.115-69 Gy) and heating rate (0. 5-10 degrees C/s) on TL intensity of Sm3+ doped ZnB2O4 phosphors and reproducibility are investigated using a lexsyg smart TL/OSL reader system. The activation energy values, E obtained from the analysis of the TL glow curve were calculated with initial rise (IR) method and peak shape (PS) method over the deconvoluted glow curves. The E-a-T-stop and CGCD methods indicated that the glow curve of this phosphor is the superposition of at least six components, which were called to as P1-P6, in the temperature range between RT and 400 degrees C. The results reveal that 2% Sm3+ doped ZnB2O4 gives optimum TL response, the relative intensity of the glow peak increases linearly with increase of beta dose and, the peaks of TL glow curves shift towards the higher temperature side with increase in heating rate as the total area under the glow peak remains the same. The maximum variation of reproducibility for ten successive irradiation cycles of 20.7 Gy is less than 3% from the average value and the sample doped 2% Sm3+ shows a good stability for the reusability. Additionally, the results obtained from IR and PS methods indicates that the complex glow curve is composed of six distinguishable peaks.