Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Effect of sintering temperature on dosimetric properties of BeO ceramic pellets synthesized using precipitation method
Introduction
Beryllium Oxide (BeO) is a high melting material (m.p. 2550 °C) with a remarkably high thermal conductivity (λ100°C = 210 W/mK), an excellent thermal shock resistance and a high chemical stability with breaking strength comparable to that of α-Al2O3. Unfortunately, the industrial production of BeO is more expensive than that of α-Al2O3; moreover, there is no broad use for BeO as its abrasive dust is highly toxic. Besides these, its high electrical resistivity (>1013 Ω·cm), hardness (1250 kg/mm2), high transparency over wide spectral range (121–7000 nm), a low thermal neutron cross-section (10 mb), made it useful as a material of heat sink, thermal shock resistance (refractory ware), high efficiency moderator and reflector in electronic and nuclear industry. BeO is a binary oxide semiconductor that possesses the wurtzite structure with a hexagonal crystal structure and possesses a direct band gap of 10.6 eV [1], [2], [3].
As well as the features mentioned above, since BeO is a tissue equivalent material (Z = 7.13), it has attracted the attention of many researchers in radiation dosimetry applications. The history of BeO begins with the study of the possibility of using visible photons, as stimulation source, to obtain the UV emission from a slurry of powdered BeO after the irradiation with X-ray [4]. According to the study by Scarpa [5], a commercial sintered BeO was considered as a very promising thermoluminescent material which may be worked in mixed fields of thermal neutrons and γ-rays. The usage of delayed OSL from disks and powder samples of BeO for radiation dosimetry was first suggested by Rhyner and Miller [6].
Many reports related to luminescence characteristics of the commercial BeO chips (Thermalox 995) have been published using thermoluminescence (TL) in detail [7], [8], [9], [10], [11]. It was announced that the glow curve of the commercial BeO ceramics has light-sensitive TL peaks and it could be a problem for TL dosimetry applications.
After the properties of BeO chips (Thermalox 995) using OSL were firstly reported in detail by Bulur and Goksu [12], considerable interest has centered on the material for OSL dosimetry. Sommer and Henniger, Sommer et al. [13], [14], [15] developed an OSL dosimetry system based on the outstanding optical properties of Thermalox 995. Meanwhile, Bulur [16] investigated TL properties and photo-transferred luminescence signals of this material. BeO was also studied using the LM-OSL technique by Bulur and Yeltik [17]. At the same time, Watanabe et al. [3] investigated TL, OSL and ESR properties in irradiated Thermalox 995. Yukihara [18] has reported a study on the same material related to the time-resolved OSL (TR-OSL). A further study of TR-OSL signals of Thermalox 995 can be seen in the work of [19], [20]. Recently, Yukihara et al. [21] have reported a protocol for new users studying BeO chips for different purposes in radiation dosimetry using an automated research OSL readers.
On the other hand, the thermoluminescence properties of synthesized BeO in ceramic and polycrystalline powder forms were investigated by various authors. Yamashita et al. [22] synthesized BeO doped with (Li, Na, Si, Ge, B, and Al) for TLD using Solid State Synthesis Method sintered at 1500 °C. The dose and energy response, emission spectrums and TL fading properties of BeO doped with Li or Na were reported to be acceptable. TL and ESR characteristics of two types BeO transparent ceramics were studied by Kortov et al. [23] using 1200 and 1600 °C sintering temperatures. They reported that the optically transparent high-density BeO ceramics, simultaneously doped with Li and Nd gave the best results. Additionally, TL properties were studied both by Ogorodnikov et al. [24] for BeO single crystals doped with B or Li impurities in different concentrations and by Kortov and Milman [25] for the transparent BeO doped with Li. Transparent BeO ceramics doped with a number of impurities, which were prepared by hot pressing at a temperature not higher than 1250 °C and a pressure of 30 MPa, were offered for ionizing radiation dosimetry as an alternative dosimetric material by Kiiko [26]. He also suggested it for being used in laser technology as material for fabrication of dielectric resonant tubes, waveguides, and dielectric non-transmitting mirrors. Recently, Wang et al. [27] synthesized BeO nanoparticles using polyacrylamide gel route and determined the most appropriate sintering temperature as 1600 °C. Zahedifar et al. [28] studied the usability of nanomaterial BeO doped with Mg synthesized with the sol-gel method, for TL dosimetry. Altunal et al. [29] synthesized undoped BeO nano-phosphor using the sol-gel method and the BeO pellets prepared from nanopowders sintered at 1100 °C. The OSL signals of these BeO pellets were reported to be nearly linear in the dose range from 0.1 to 100 Gy; thermally stable up to 150 °C; fade about 11% in about a week of dark storage and dominated by fast decay component.
The available experimental results on BeO, in the literature, however, provided luminescence data mostly over Thermalox 995 either using TL or OSL and usually investigated significant experimental results for its interpretation. To the author's knowledge, a complete study of synthesized BeO material by TL and OSL has not yet been undertaken deeply. In this paper, we attempt to bridge this gap reporting experimental measurements of the TL and OSL luminescence and their sintering temperature dependence for BeO.
In this study, we synthesized the BeO polycrystalline powder material using precipitation method and used cold molding to shape it in pellets. All the pellets employed in luminescence measurements were sintered at 1200, 1400 and 1600 °C, for 4 h for comparison studies. Structural, morphological and luminescent properties were investigated. The first objective of this work is to take advantage of the gain in OSL efficiency that is to be expected from the use of high (1600 °C) sintering temperature. Another objective is to determine whether there exist changes in the relative OSL response, reusability and fading characteristics due to the sintering temperature dependent variations in synthesized BeO or not.
Section snippets
Synthesis of BeO
BeO powders were synthesized using precipitation synthesis route. In this method, polyethyleneimine solution (Sigma-Aldrich, analytical standard, 50% (w/v) in H2O) for polymerization and ammonium hydroxide solution (NH4OH) (Sigma-Aldrich, ACS reagent, 28.0–30.0% NH3 basis) as an initiator of the precipitate were used. As the precursor reactant, beryllium sulfate tetra-hydrate (BeSO4·4H2O) (Aldrich, 99.99% trace metals basis) was used. A general experimental procedure of this method is as
Characterization of BeO
After sintering BeO pellets at three different temperatures (1200, 1400 and 1600 °C, for 4 h), XRD analyzes of the BeO pellets were performed to investigate the role of the sintering temperature on the crystal structure of BeO. Fig. 1 shows the phase identification of BeO pellets sintered for 4 h, as a function of sintering temperature, using the XRD pattern. Analysis of the XRD data showed that all of the reflections are assigned to BeO phase with hexagonal structure. The patterns of BeO
Conclusion
This work was done on BeO pellets prepared using the precipitation method and sintered at 1200, 1400 and 1600 °C. The variation of the structural, morphological and relevant dosimetric and luminescent properties of the BeO pellets was investigated as a function of the sintering temperatures.
The structural and morphological investigations revealed that the pellets have the polycrystalline wurtzite structure with a hexagonal crystal structure. With increasing sintering temperature, the
Acknowledgment
This research is sponsored by the Cukurova University Rectorate through the projects FDK-2018-10190. We gratefully acknowledge the financial support given by Cukurova University. We very much appreciate Prof. Enver Bulur for his valuable discussions and comments, Prof. Dr. Kasım Kurt for XL measurements, and Prof. Bekir Özçelik for his valuable advice and helps.
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