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Performance and Characterization of CsI:Tl thin Films for X-ray Imaging Application
Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 84 (2016) 245 – 251
International Conference “Synchrotron and Free electron laser Radiation: generation and application”, SFR-2016, 4-8 July 2016, Novosibirsk, Russia
Performance and characterization of CsI:Tl thin films for X-ray imaging application E.A. Kozyreva,b,∗, K.E. Kupera , A.G. Lemzyakova , A.V. Petrozhitskiya , A.S. Popova a Budker
Institute of Nuclear Physics, SB RAS, Novosibirsk, 630090, Russia State University, Novosibirsk, 630090, Russia
b Novosibirsk
Abstract High spatial resolution thin CsI:Tl scintillator films was prepared by thermal deposition method for X-ray imaging applications. We fabricated CsI:Tl scintillators ranging from 2 μm to 14 μm in thickness. We measured spacial resolution and light yield as a function of input photons energy (5-40 keV) and film thickness. To improve spatial resolution of films carbon post-deposition treatments was performed. © Authors. Published by Elsevier B.V. This c 2016 2016The The Authors. Published by Elsevier B.V. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SFR-2016. Peer-review under responsibility of the organizing committee of SFR-2016. Keywords: high-resolution, CsI:Tl, thin scintillator films, X-ray imaging, vacuum deposition method, carbon layer
1. Introduction CsI:Tl scintillator films are widely applied as the conversion screens for the indirect X-ray imaging. The CsI:Tl is characterized by one of the highest conversion efficiencies of any known scintillator (Nikl (2006)). There are a lot of researches where authors consider different approaches to the performance of the scintillator films. The methods to fabricate thin scintillators using a vacuum deposition process have been developed since the 1960s by Bates (1969). In general, there are two approach to improve spatial resolution of the X-ray image obtained using the scintillators. The first one consists in the growth of CsI:Tl scintillator with micro-columnar structure (Nagarkar et al. (1998, 2001); Yao et al. (2013)). The micro-structure of the crystals of the scintillator decreases the lateral spreading of scintillating light. The second approach consider post-deposition additional coating by carbon to decrease multiple scattering of photons inside scintillator volume (Zhao-Dong et al. (2015)). It is observed that the intrinsic properties of the structured CsI:Tl screens are heavily influenced by post deposition carbon coating. In the research we study the influence of carbon layer to spatial resolution and light output of the films with different thicknesses and energy of input X-ray photons. Additionally, the paper is dedicated to demonstrate the X-ray imaging applications of thin scintillator films. ∗
Corresponding author. Tel.: +7-383-329-4709. E-mail address: [email protected]
1875-3892 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SFR-2016. doi:10.1016/j.phpro.2016.11.042
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E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251
Fig. 1. Schematic of the thermal evaporation setting.
Fig. 2. Scintillator morphology of CsI:Tl film deposited on glass substrate with thickness 4.1±0.3 μm.
2. Experimental 2.1. Preparation of CsI:Tl Scintillation Films CsI:Tl scintillation films were manufactured by the thermal deposition method. We use glass substrates with 150 μm thickness and 25x25 mm2 area. The source material - CsI:Tl held in a tantalum boat. The doping concentration of Tl was about 0.08 mol%. During deposition process the tantalum boat temperature was set at 680◦ C as a nominal value. To achieve homogeneous coverage of substrate by scintillator a relatively low deposition rate (17 ± 2 Å/s) was used. All samples were prepared at pressure of 5·10−3 Pa and substrate temperature at 25◦ C as was recommended by Thornton Zone Model (Thornton (1974)). A rotated disk with substrates was situated at distance 65 cm from tantalum boat (see Fig. 1). Four thicknesses of CsI:Tl films were prepared: about 2, 4, 8 and 14 μm. It was observed that Tl concentration decreases with the increase of deposition time. The Tl density in 8 μm sample is less by 1.2÷1.3 times relatively to 2 μm sample, due to larger evaporation velocity of Tl relatively to CsI. So, the deposited on substrate CsI:Tl scintillator is characterized by acceptable Tl concentration for the thicknesses less than 10 μm. For larger thicknesses we need apply serial deposition procedure step-by-step increasing the CsI:Tl layer. Scintillator morphology of CsI:Tl film deposited on glass substrate was investigated by a scanning electron microscope and is shown in Fig. 2. The film consists of well-defined grain structure with typical size of the grain about 2÷5 μm. In order to improve spatial resolution of obtained scintillator screens we perform additional carbon layer on CsI:Tl surface by magnetron deposition method using AUTO 500 Vacuum Coater (BOC EDWARDS corp.). All images that will be shown below was generated using CsI:Tl films with 70 nm carbon layer, unless otherwise stated.
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Fig. 3. Layout of experimental setup for examination thin scintillator films.
2.2. Micro-structure measurement and quantification of X-ray imaging performance The examination thin films scintillator was carried out at ”Microscopy and tomography” beamline of the VEPP-3 synchrotron source (BINP, Novosibirsks). The stability electron orbit in VEPP-3 storage ring was better than 50 μm and electron bunch with size 0.5x1.5 mm2 provided spatial resolution around 1 μm. The experimental setup is shown schematically in Fig. 3. A detector of visible light placed at a distance 5 cm from the scintillator screen. The CsI:Tl film was fixed towards to the X-ray source while glass substrate is directed to the optical detector. The X-ray working wavelength was selected by a double-crystal Si (111) monochromator used in the parallel Bragg-geometry and was installed at a distance of 14.5 m from the synchrotron radiation (SR) emission point. The energy of photons of X-ray monochromatic beams, used in the experiments, varied from 5 to 40 keV. Slits installed upstream the sample were applied for suppression of parasitic reflections from the monochromator and formed a 2x2 mm2 collimated X-ray beam. The scintillator was placed at a distance of 16.5 m from the SR source. The visible light from scintillator was collected by precise digital camera Hamamatsu ORCA-Flah2.8. The scintillator was pre-aligned in a translated axis with accuracy of 10 μm and in a rotation axis with an accuracy of 0.01 degree. 3. Results and Discussion 3.1. Spatial resolution In order to test intrinsic spatial resolution of resulting system (the Fig. 3) we take the images of gold patterns that produced in BINP. The patterns are manufactured by e-beam lithography (SEM HITACHI S 3400 type II with Nanomaker system). The PMMA 950k e-beam positive tone resist with 2 μm thickness was used. The X-ray absorber pattern was obtained by gold electroplating. Fig. 4 (a) corresponds to SEM image of the patterns where numbers mean the correspond width. The Fig. 4 (b) was obtained using X-ray imaging technique with 2 μm thickness CsI:Tl screen. The image of the pattern with 6 μm width can be reasonable resolved. The image also demonstrates that the response of X-ray conversation screen is uniform across the area of the film. It should be mentioned that total spatial resolution of the system is caused, predominantly, by the following factors: non-collinearity of incident X-ray beam, mechanical oscillation of the holder of detector relatively to beam line and lateral spreading of visible photons inside scintillator volume. The last two reasons are characterized by more or less comparable contributions. We use anti-vibration pltform to reduce the contribution of the vibrations. The modulation transfer function MTF(f) for spatial frequencies in the range of 0 to 160 lp/mm for various screens was calculated from the Fast Fourier Transform of the line spread function (LSF) data. The LSF was obtained by the edge method using steel plate with thickness 1 mm placed in front of the scintillator. Fig. 5 shows the measured spatial resolution in term of the MTF(f) for screens of various thickness. The lines 2, 4, 5, 6 correspond to films with 14, 8, 4, 2 μm of CsI:Tl and 70 nm carbon layers, respectively. It is seen that there is a reduction in resolution with increased film thickness due to lateral light spreading and not perfect channeling inside scintillator volume. This dependence is in agreement with previous results reported by Zhao-Dong et al. (2015); Zhao et al. (2009) and illustrates that our scintillation screens are characterized by micro-columnar structure. The most thin 2 μm screen provides as the highest spatial resolution required for applications such as low energy micro-tomography of biological objects and as high stopping power of X-ray beam. For example, the conversation efficiency of X-ray beam in the 2 μm screen is still 20% at 9 keV of incident X-ray.
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Fig. 4. Image of gold patterns obtained by SEM (a) and X-ray imaging technique using CsI:Tl films (b).
In order to demonstrate the improvement of resolution, related with the carbon deposition, we calculate MTF(f) of patterns with different conditions. So, lines 1, 2, 3 in the Fig. 5 correspond to screen with 14 μm thickness of CsI:Tl and with 0, 70 and 140 nm of carbon, respectively. The improvement can be explained as the following. The additional carbon layer suppresses the reflection of scintillation photons on the interface between carbon layer and CsI:Tl, removing the multiple scattering of visible photons inside scintillator volume. Simultaneously, the additional carbon layer leads to decrease of light output to a factor 2.5÷3.5. The factor is significantly lager than 2 that indicates to the presence of multiple reflection between scintillator boundaries. Fig. 6 demonstrates measured MTF curves of CsI:Tl scintillator screen obtained at different incident X-ray beam energies. It was observed that there are no significant improvement of spatial resolution with increase of X-ray energy from 7 to 35 keV.
3.2. 3-D tomography We used the high resolution images obtained by applying our thin scintillator film to reconstructed 3D structures different samples by method X- ray computed tomography. Each tomography scan consists of 720 projections with an angular step of 0.25◦ (from 0◦ to 180◦ ) obtained at monochromatic beam with photons energy 15 keV. Small angle SR deviation of about 0.2 mrad makes it possible to use an algorithm for a parallel beam geometry, which simplifies the process of 3D reconstruction of the object and significantly improves the quality of the image. The example 3D structure of small piece of Chelyabinsk meteorite with spatial resolution about 5 μm is demonstrated in Fig. 7. 3D image of meteorite essentially represents a density map of the sample, from which one can extract the sizes, shapes, textures, and locations of individual inclusions. 3D models of the samples reveal clearly the spatial relationships between metal incisions (red color) and their surroundings. This may be to give the key to understanding the thermal processes occurring in the meteorites during to propagation in Earth atmosphere. To investigate objects which are bigger than field of view of our detector by nondestructive method we use local computed tomography mode and polychromatic beam with average photon energy about 25 keV. Fig. 8 depicts 3D image of selected area inside compound detail which is applied in aerospace technology. The shown structure demonstrates high quality of its performance due to homogeneous distribution of different components without cracks and pores.
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E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251 1 0.9 0.8 0.7
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Fig. 5. Measured MTF curves of CsI:Tl scintillating screens with 1. 14 μkm of CsI:Tl without carbon layer (14-0); 2. 14 μkm of CsI:Tl + 70 nm of carbon (14-70); 3. 14-140; 4. 8-70; 5. 4-70; 6. 2-70.
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Fig. 6. Measured MTF curves of CsI:Tl scintillator screen with 8 μm thickness obtained at different energies of incident X-ray beam.
3.3. Other prospects Additionally, thin CsI:Tl films deposited on Mylar substrates can be used for non-destructive diagnostics of the spatial profiles of low energy beams of charge particles (ex., muon beams at MEG experiment). The proposed method allows to perform the beam monitoring simultaneously with experimental data acquisition. Also the developed technique of CsI:Tl deposition allow to perform low cost X-ray converters with arbitrary thickness, that can be used in medicine and etc.
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Fig. 7. The tomography of piece of Chelyabinsk meteorite.
Fig. 8. 3D image of selected area inside compound detail which is applied in aerospace technology.
4. Conclusion We developed the technique of performance of thin CsI:Tl films by thermal deposition method. It was proposed that the spatial resolution of prepared conversation screens can be significantly improved by additional deposition of
E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251
carbon layer with thickness about 100 nm which is designed to absorb photons propagated in backward direction. All X-ray low energy radio-graphic methods can be employed with the films in polychromatic and monochromatic modes to investigate the internal structure of wide range types of objects varied from 10 μm of biological tissue up to 10 cm of dense rock. 5. Acknowledgments The work relating to the measurement of scintillator film properties was done using the infrastructure of the SharedUse Center ”Siberian Synchrotron and Terahertz Radiation Center (SSTRC)” based on VEPP-3 of BINP SB RAS. Also this research is supported by the Russian Science Foundation (project 14-50-00080). References Martin Nikl, Scintillation detectors for x-ray, Meas. Sci. Technol. 17 (2006). C.W. Bates, Scintillation Processes in Thin Films of CsI(Na) and CsI(Tl) used to Low Energy X-rays, Electrons and Protons, in Photo-Electronic Image Devices, Eds. J.D. McGee, D. McMillan, E. Kahan, B.L. Morgan, pp. 451-459, Academic Press, London-New York (1969). V.V. Nagarkar, T.K. Gupta, S.R. Miller, Y. Klugerman, M.R. Squillante, Structured CsI(Tl) Scintillators for X-ray Imaging Applications. IEEE Trans. Nucl. Sci, 45, pp. 492-496, (1998). V.V. Nagarkar, S. V. Tipnis, S.R. Miller, and V. B. Gaysinskiy, A Comparative Study of CsI(Tl) Screens for Macromolecular Crystallography, Proc. SPIE, Vol. 4508, pp.15-19, (2001). D. Yao, et al., IEEE Transactions on Nuclear Science, 60, 3 (2013). F. Zhao-Dong, et al., Chinese Phys. C 39 078202 (2015). B.Z. Zhao, X.B. Qin, Z.D. Feng, et al. Chinese Physics C, 38 116003 (2009). J.A. Thornton, ”Influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings”, J. Vac. Sci. Technol. 11 (1974).
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ScienceDirect Physics Procedia 84 (2016) 245 – 251
International Conference “Synchrotron and Free electron laser Radiation: generation and application”, SFR-2016, 4-8 July 2016, Novosibirsk, Russia
Performance and characterization of CsI:Tl thin films for X-ray imaging application E.A. Kozyreva,b,∗, K.E. Kupera , A.G. Lemzyakova , A.V. Petrozhitskiya , A.S. Popova a Budker
Institute of Nuclear Physics, SB RAS, Novosibirsk, 630090, Russia State University, Novosibirsk, 630090, Russia
b Novosibirsk
Abstract High spatial resolution thin CsI:Tl scintillator films was prepared by thermal deposition method for X-ray imaging applications. We fabricated CsI:Tl scintillators ranging from 2 μm to 14 μm in thickness. We measured spacial resolution and light yield as a function of input photons energy (5-40 keV) and film thickness. To improve spatial resolution of films carbon post-deposition treatments was performed. © Authors. Published by Elsevier B.V. This c 2016 2016The The Authors. Published by Elsevier B.V. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SFR-2016. Peer-review under responsibility of the organizing committee of SFR-2016. Keywords: high-resolution, CsI:Tl, thin scintillator films, X-ray imaging, vacuum deposition method, carbon layer
1. Introduction CsI:Tl scintillator films are widely applied as the conversion screens for the indirect X-ray imaging. The CsI:Tl is characterized by one of the highest conversion efficiencies of any known scintillator (Nikl (2006)). There are a lot of researches where authors consider different approaches to the performance of the scintillator films. The methods to fabricate thin scintillators using a vacuum deposition process have been developed since the 1960s by Bates (1969). In general, there are two approach to improve spatial resolution of the X-ray image obtained using the scintillators. The first one consists in the growth of CsI:Tl scintillator with micro-columnar structure (Nagarkar et al. (1998, 2001); Yao et al. (2013)). The micro-structure of the crystals of the scintillator decreases the lateral spreading of scintillating light. The second approach consider post-deposition additional coating by carbon to decrease multiple scattering of photons inside scintillator volume (Zhao-Dong et al. (2015)). It is observed that the intrinsic properties of the structured CsI:Tl screens are heavily influenced by post deposition carbon coating. In the research we study the influence of carbon layer to spatial resolution and light output of the films with different thicknesses and energy of input X-ray photons. Additionally, the paper is dedicated to demonstrate the X-ray imaging applications of thin scintillator films. ∗
Corresponding author. Tel.: +7-383-329-4709. E-mail address: [email protected]
1875-3892 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SFR-2016. doi:10.1016/j.phpro.2016.11.042
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Fig. 1. Schematic of the thermal evaporation setting.
Fig. 2. Scintillator morphology of CsI:Tl film deposited on glass substrate with thickness 4.1±0.3 μm.
2. Experimental 2.1. Preparation of CsI:Tl Scintillation Films CsI:Tl scintillation films were manufactured by the thermal deposition method. We use glass substrates with 150 μm thickness and 25x25 mm2 area. The source material - CsI:Tl held in a tantalum boat. The doping concentration of Tl was about 0.08 mol%. During deposition process the tantalum boat temperature was set at 680◦ C as a nominal value. To achieve homogeneous coverage of substrate by scintillator a relatively low deposition rate (17 ± 2 Å/s) was used. All samples were prepared at pressure of 5·10−3 Pa and substrate temperature at 25◦ C as was recommended by Thornton Zone Model (Thornton (1974)). A rotated disk with substrates was situated at distance 65 cm from tantalum boat (see Fig. 1). Four thicknesses of CsI:Tl films were prepared: about 2, 4, 8 and 14 μm. It was observed that Tl concentration decreases with the increase of deposition time. The Tl density in 8 μm sample is less by 1.2÷1.3 times relatively to 2 μm sample, due to larger evaporation velocity of Tl relatively to CsI. So, the deposited on substrate CsI:Tl scintillator is characterized by acceptable Tl concentration for the thicknesses less than 10 μm. For larger thicknesses we need apply serial deposition procedure step-by-step increasing the CsI:Tl layer. Scintillator morphology of CsI:Tl film deposited on glass substrate was investigated by a scanning electron microscope and is shown in Fig. 2. The film consists of well-defined grain structure with typical size of the grain about 2÷5 μm. In order to improve spatial resolution of obtained scintillator screens we perform additional carbon layer on CsI:Tl surface by magnetron deposition method using AUTO 500 Vacuum Coater (BOC EDWARDS corp.). All images that will be shown below was generated using CsI:Tl films with 70 nm carbon layer, unless otherwise stated.
E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251
Fig. 3. Layout of experimental setup for examination thin scintillator films.
2.2. Micro-structure measurement and quantification of X-ray imaging performance The examination thin films scintillator was carried out at ”Microscopy and tomography” beamline of the VEPP-3 synchrotron source (BINP, Novosibirsks). The stability electron orbit in VEPP-3 storage ring was better than 50 μm and electron bunch with size 0.5x1.5 mm2 provided spatial resolution around 1 μm. The experimental setup is shown schematically in Fig. 3. A detector of visible light placed at a distance 5 cm from the scintillator screen. The CsI:Tl film was fixed towards to the X-ray source while glass substrate is directed to the optical detector. The X-ray working wavelength was selected by a double-crystal Si (111) monochromator used in the parallel Bragg-geometry and was installed at a distance of 14.5 m from the synchrotron radiation (SR) emission point. The energy of photons of X-ray monochromatic beams, used in the experiments, varied from 5 to 40 keV. Slits installed upstream the sample were applied for suppression of parasitic reflections from the monochromator and formed a 2x2 mm2 collimated X-ray beam. The scintillator was placed at a distance of 16.5 m from the SR source. The visible light from scintillator was collected by precise digital camera Hamamatsu ORCA-Flah2.8. The scintillator was pre-aligned in a translated axis with accuracy of 10 μm and in a rotation axis with an accuracy of 0.01 degree. 3. Results and Discussion 3.1. Spatial resolution In order to test intrinsic spatial resolution of resulting system (the Fig. 3) we take the images of gold patterns that produced in BINP. The patterns are manufactured by e-beam lithography (SEM HITACHI S 3400 type II with Nanomaker system). The PMMA 950k e-beam positive tone resist with 2 μm thickness was used. The X-ray absorber pattern was obtained by gold electroplating. Fig. 4 (a) corresponds to SEM image of the patterns where numbers mean the correspond width. The Fig. 4 (b) was obtained using X-ray imaging technique with 2 μm thickness CsI:Tl screen. The image of the pattern with 6 μm width can be reasonable resolved. The image also demonstrates that the response of X-ray conversation screen is uniform across the area of the film. It should be mentioned that total spatial resolution of the system is caused, predominantly, by the following factors: non-collinearity of incident X-ray beam, mechanical oscillation of the holder of detector relatively to beam line and lateral spreading of visible photons inside scintillator volume. The last two reasons are characterized by more or less comparable contributions. We use anti-vibration pltform to reduce the contribution of the vibrations. The modulation transfer function MTF(f) for spatial frequencies in the range of 0 to 160 lp/mm for various screens was calculated from the Fast Fourier Transform of the line spread function (LSF) data. The LSF was obtained by the edge method using steel plate with thickness 1 mm placed in front of the scintillator. Fig. 5 shows the measured spatial resolution in term of the MTF(f) for screens of various thickness. The lines 2, 4, 5, 6 correspond to films with 14, 8, 4, 2 μm of CsI:Tl and 70 nm carbon layers, respectively. It is seen that there is a reduction in resolution with increased film thickness due to lateral light spreading and not perfect channeling inside scintillator volume. This dependence is in agreement with previous results reported by Zhao-Dong et al. (2015); Zhao et al. (2009) and illustrates that our scintillation screens are characterized by micro-columnar structure. The most thin 2 μm screen provides as the highest spatial resolution required for applications such as low energy micro-tomography of biological objects and as high stopping power of X-ray beam. For example, the conversation efficiency of X-ray beam in the 2 μm screen is still 20% at 9 keV of incident X-ray.
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Fig. 4. Image of gold patterns obtained by SEM (a) and X-ray imaging technique using CsI:Tl films (b).
In order to demonstrate the improvement of resolution, related with the carbon deposition, we calculate MTF(f) of patterns with different conditions. So, lines 1, 2, 3 in the Fig. 5 correspond to screen with 14 μm thickness of CsI:Tl and with 0, 70 and 140 nm of carbon, respectively. The improvement can be explained as the following. The additional carbon layer suppresses the reflection of scintillation photons on the interface between carbon layer and CsI:Tl, removing the multiple scattering of visible photons inside scintillator volume. Simultaneously, the additional carbon layer leads to decrease of light output to a factor 2.5÷3.5. The factor is significantly lager than 2 that indicates to the presence of multiple reflection between scintillator boundaries. Fig. 6 demonstrates measured MTF curves of CsI:Tl scintillator screen obtained at different incident X-ray beam energies. It was observed that there are no significant improvement of spatial resolution with increase of X-ray energy from 7 to 35 keV.
3.2. 3-D tomography We used the high resolution images obtained by applying our thin scintillator film to reconstructed 3D structures different samples by method X- ray computed tomography. Each tomography scan consists of 720 projections with an angular step of 0.25◦ (from 0◦ to 180◦ ) obtained at monochromatic beam with photons energy 15 keV. Small angle SR deviation of about 0.2 mrad makes it possible to use an algorithm for a parallel beam geometry, which simplifies the process of 3D reconstruction of the object and significantly improves the quality of the image. The example 3D structure of small piece of Chelyabinsk meteorite with spatial resolution about 5 μm is demonstrated in Fig. 7. 3D image of meteorite essentially represents a density map of the sample, from which one can extract the sizes, shapes, textures, and locations of individual inclusions. 3D models of the samples reveal clearly the spatial relationships between metal incisions (red color) and their surroundings. This may be to give the key to understanding the thermal processes occurring in the meteorites during to propagation in Earth atmosphere. To investigate objects which are bigger than field of view of our detector by nondestructive method we use local computed tomography mode and polychromatic beam with average photon energy about 25 keV. Fig. 8 depicts 3D image of selected area inside compound detail which is applied in aerospace technology. The shown structure demonstrates high quality of its performance due to homogeneous distribution of different components without cracks and pores.
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E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251 1 0.9 0.8 0.7
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Fig. 5. Measured MTF curves of CsI:Tl scintillating screens with 1. 14 μkm of CsI:Tl without carbon layer (14-0); 2. 14 μkm of CsI:Tl + 70 nm of carbon (14-70); 3. 14-140; 4. 8-70; 5. 4-70; 6. 2-70.
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Fig. 6. Measured MTF curves of CsI:Tl scintillator screen with 8 μm thickness obtained at different energies of incident X-ray beam.
3.3. Other prospects Additionally, thin CsI:Tl films deposited on Mylar substrates can be used for non-destructive diagnostics of the spatial profiles of low energy beams of charge particles (ex., muon beams at MEG experiment). The proposed method allows to perform the beam monitoring simultaneously with experimental data acquisition. Also the developed technique of CsI:Tl deposition allow to perform low cost X-ray converters with arbitrary thickness, that can be used in medicine and etc.
250
E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251
Fig. 7. The tomography of piece of Chelyabinsk meteorite.
Fig. 8. 3D image of selected area inside compound detail which is applied in aerospace technology.
4. Conclusion We developed the technique of performance of thin CsI:Tl films by thermal deposition method. It was proposed that the spatial resolution of prepared conversation screens can be significantly improved by additional deposition of
E.A. Kozyrev et al. / Physics Procedia 84 (2016) 245 – 251
carbon layer with thickness about 100 nm which is designed to absorb photons propagated in backward direction. All X-ray low energy radio-graphic methods can be employed with the films in polychromatic and monochromatic modes to investigate the internal structure of wide range types of objects varied from 10 μm of biological tissue up to 10 cm of dense rock. 5. Acknowledgments The work relating to the measurement of scintillator film properties was done using the infrastructure of the SharedUse Center ”Siberian Synchrotron and Terahertz Radiation Center (SSTRC)” based on VEPP-3 of BINP SB RAS. Also this research is supported by the Russian Science Foundation (project 14-50-00080). References Martin Nikl, Scintillation detectors for x-ray, Meas. Sci. Technol. 17 (2006). C.W. Bates, Scintillation Processes in Thin Films of CsI(Na) and CsI(Tl) used to Low Energy X-rays, Electrons and Protons, in Photo-Electronic Image Devices, Eds. J.D. McGee, D. McMillan, E. Kahan, B.L. Morgan, pp. 451-459, Academic Press, London-New York (1969). V.V. Nagarkar, T.K. Gupta, S.R. Miller, Y. Klugerman, M.R. Squillante, Structured CsI(Tl) Scintillators for X-ray Imaging Applications. IEEE Trans. Nucl. Sci, 45, pp. 492-496, (1998). V.V. Nagarkar, S. V. Tipnis, S.R. Miller, and V. B. Gaysinskiy, A Comparative Study of CsI(Tl) Screens for Macromolecular Crystallography, Proc. SPIE, Vol. 4508, pp.15-19, (2001). D. Yao, et al., IEEE Transactions on Nuclear Science, 60, 3 (2013). F. Zhao-Dong, et al., Chinese Phys. C 39 078202 (2015). B.Z. Zhao, X.B. Qin, Z.D. Feng, et al. Chinese Physics C, 38 116003 (2009). J.A. Thornton, ”Influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings”, J. Vac. Sci. Technol. 11 (1974).
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