GAGG:Ce composite scintillator for X-ray imaging
Introduction
Nowadays gadolinium aluminum gallium garnet Gd3Al5-xGaxO12:Ce (GAGG:Ce) is considered as the most efficient oxide scintillator [[1], [2], [3], [4]]. It possesses a high light yield up to 50000–60000 phot/MeV and a good energy resolution [[5], [6], [7]]. Its other advantages include the high density of 6.63 g/cm3, high Zeff = 54, unhygroscopicity, a relatively short scintillation decay time of around 55 ns, the presence of Gd, which is the element with the highest neutron capture cross section [[8], [9], [10]]. Digital radiography is one of the possible applications of GAGG:Ce since the development of this material [11]. A good performance of GAGG:Ce for X-ray detection was demonstrated [[11], [12], [13], [14], [15], [16], [17], [18]]. A scintillator layer thickness is one of the main features of such detectors. While it should be thin enough to provide a high spatial resolution, the sufficient thickness is necessary for complete X-ray absorption. There are several methods to form the detection layer, including the thin film deposition, and growing and cutting of bulk crystals. For example, 60 μm thick GAGG:Ce single crystalline plates were fabricated from bulk crystals for Synchrotron X-Ray Micro-Imaging [19]. Ceramic samples for X-ray CT detectors were fabricated in Refs. [20,21]. Thin films of Gd3Al5-xGaxO12:Ce were proposed for electron detection in Scanning Electron Microscopy [22]. In Ref. [23], GAGG nanopowders were used as the sensitive element embedded into the organic matrix of the composite scintillator. Meanwhile, nanopowder synthesis is labor consuming and expensive process, especially in case of large-scale production. Organic reagents used for nanoparticle synthesis are the source of undesirable admixtures in finish products. Therefore, nanoparticles substitution with powders prepared by a standard solid-state synthesis would be helpful. Some authors of this work have performance in development of the composition detectors based on powders or ground single crystals of Y2SiO5:Ce, Y3Al5O12:Ce, ZnSe:Te, Lu2-xGdxSiO5:Ce scintillators distributed in the organic binder [[24], [25], [26], [27]]. Apart of a lower production cost, such approach in fact removes the limits on the square and shape of composite scintillation detectors.
This work deals with the solid-state synthesis of GAGG:Ce powders and testing the performance of composite scintillation detectors on their base for X-ray radiography.
Section snippets
GAGG:Ce powder and composite preparation
GAGG:Ce samples with the compositions (Gd1-xCex)3(Al0,48Ga0,52)5O12 (x = 0.0002–0.009) were synthesized by the solid state synthesis. The Gd2O3, Al2O3, Ga2O3, CeO2 initial components were accurately mixed and isostatically pressed, then the pellets were calcined in Ir crucible under Ar atmosphere. The following GAGG:Ce synthesis temperatures were chosen: lower than 2/3 of the melting temperature according to the Tamman criterion [28], and around 90% of the melting temperature. As the GAGG:Ce
Structure of composite detectors
The view of GAGG:Ce synthesized at different temperatures is presented in Fig. 1 (a, b) One can see that the powders synthesized at 1350°С (Fig. 1а) and at 1600°С (Fig. 1b) have the different color. This may be attributed to incomplete solid phase reaction between the components at lower temperature and/or incomplete transfer of cerium from Ce4+ to optically active Ce3+ valence state.
General view of the composite scintillators based on GAGG:Ce powder and typical GAGG:Ce granules sizes are
Conclusions
Composite scintillation detectors for X-ray imaging based on GAGG:Ce grains synthesized by the solid state reaction were developed. The highest X-ray luminescence intensity was achieved at 1600 °С powder calcination temperature and the Ce concentration of 0.12 at. % in GAGG:Ce. The deviation of light output over the detector square does not exceed ±6%. The spatial resolution of 4 lp/mm was achieved on X-ray images obtained by the developed composite scintillator with the 0.1 mm thickness. This
Authorship contribution statement
Ia Gerasymov: Methodology, Development or design of methodology, creation of models. Writing - review & editing, Preparation, creation and/or presentation of the published work by those from the original research group, specifically critical review, commentary or revision – including pre-or postpublication stages. T. Nepokupnaya: Methodology, Development or design of methodology; creation of models. A. Boyarintsev: Ideas; formulation or evolution of overarching research goals and aims. O.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the project No.0117U000988 «Composite» of National Academy of Science of Ukraine. We greatly acknowledge to Dr. S. Minenko for performing the absorption spectra measurements, and Dr. V. Tarasov and Dr. A. Lebedynskiy for helpful comments regarding the results interpretation.
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Authors contributed equally.