- Email: [email protected]
Development of real-time position detection system for single-ion hit
Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Development of real-time position detection system for single-ion hit A. Yokoyama a,⇑, W. Kada b, T. Satoh a, M. Koka a, S. Yamamoto a, T. Kamiya a, W. Yokota a a b
Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency (JAEA), 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japan Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-machi, Kiryu, Gunma 376-8515, Japan
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Single-ion Ion luminescence Real-time detection Photoluminescence
a b s t r a c t A real-time position detection system has been developed for a single-ion hit. The system is composed of a position sensitive camera unit and a luminescent scintillator. The camera unit includes 512 512 pixel electron-multiplier charge-coupled device, an image intensifier tube, and an object lens with a working distance of 101 mm. To obtain a highly sensitive luminescent scintillator for the detection of a single ion in the mega-electron-volt region, we investigate the photoluminescence properties of a-Al2O3 single-crystals implanted with Eu(Al2O3:Eu) at a fluence ranging from1014 to 1016 cm 2. The Al2O3:Eu samples were annealed at temperature from 500°C to 900°C. The results of 15-MeV O singleion hit experiments using Al2O3:Eu with a fluence of 3.0 1016 cm 2 annealed for 0.5 h at 600°C indicate that our system is sufficiently sensitive to detect the single-ion hit with a spatial resolution of 1 lm in real time. Ó 2014 Published by Elsevier B.V.
1. Introduction Real-time position detection of single ions is important for studying the microscopic irradiation of biological living cells [1–4]. The technology to shoot an ion at a target with a spatial accuracy of a few micrometers, called a single-ion hit, has been utilized at JAEA/Takasaki. The spatial accuracy of the single-ion hit at this facility is a few micrometers at energies of a few to hundreds of mega-electron-volt. A CR-39 plastic track detector placed under the sample is currently used to detect the position of the ions hitting the sample [5]. The CR-39 detector is made of polymerized diethyleneglycol bis allylcarbonate. The ion tracks formed in the CR-39 are observed off-line using a microscope after chemical etching [6]. Real-time position detection of the single-ion hit would provide a significant advance for the microscopic irradiation of biological cells. The detection of luminescence induced by a single ion using a ZnS:Ag powder scintillator was tested, but position resolution was insufficient because light scattering occurs around the grain boundaries in the powders and the incident ions deflect with getting into the sample. The aim of this study is to establish a position detection system for a single-ion hit using the strong ion luminescence (IL) emitted by Al2O3:Eu and a highly sensitive camera unit. Among single-crystal scintillators implanted with rare-earth ions, Al2O3:Eu (Eu is ⇑ Corresponding author. Tel.: +81 (0)27 346 9634. E-mail address: [email protected] (A. Yokoyama).
implanted into a-Al2O3 as activator), is of particular interest because of its strong luminescence under electron and ion beam irradiation [7,8]. Ion implantation is a good method for forming luminescence layer with nanometer-order in the sample for a high spatial resolution. The detection system described here is more sensitive than equivalent commercially available devices and includes image intensifier tubes, which have a maximum gain of 5 106 lm=m2 =lx, and electron-multiplier charge-coupled device (EM-CCD) camera, which have a maximum linear gain of 8 105 electrons. 2. Experimental Al2O3:Eu was prepared using ion implantation technique; mirror polished c-plane a-Al2O3 plates with a size of 10 10 mm2 and a thickness of 300 lm were used as the starting material. Ion implantation was carried out using the 400 kV ion implanter at JAEA/Takasaki and 350, 250 and 150-keV Eu ion were implanted in the same a-Al2O3 sample. The total Eu implantation fluence was varied between 3.0 1014 and 3.0 1016 cm 2. The Eu beam current was kept below 1.0 lA/cm2. To investigate the effect of defects caused by the Eu implantation on the luminescence of Al2O3:Eu, the Al2O3 samples were irradiated by 120, 80 and 50-keV Ar beam. The Ar beam was selected to form defects that did not contribute to scintillation. The Al2O3:Eu samples were annealed in an electric furnace, and the annealing temperature and annealing time were varied from 500 to 1000°C and 0 to 2.0 h, respectively.
http://dx.doi.org/10.1016/j.nimb.2014.02.090 0168-583X/Ó 2014 Published by Elsevier B.V.
Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090
2
A. Yokoyama et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
The luminescence of the Al2O3:Eu samples was characterized using photoluminescence (PL) measurements. Both PL and IL occur via the same electric excitation mechanisms. The PL measurements were carried out at room temperature using a 325-nm, 20-mW HeCd laser with 0.5-mm-diameter spot size. The PL of the Al2O3:Eu samples was detected using a high-sensitivity spectrometer and an electrically-cooled CCD camera. The pixel array of the camera was 1340 100 pixels and the pixel size was 20 20 lm. A lowcut filter was placed in front of the spectrometer to cut off the excitation wavelength of 325 nm. The IL detection system is required to have a spatial resolution of approximately 1 lm, the same as the spatial accuracy of the single-ion hit. The detection system consisted of a long-workingdistance lens, a zoom lens tube, an image intensifier with two micro-channel plates and EM-CCD camera, as shown in Fig. 1. The long-working distance lens and zoom lens tube had optical magnifications that could be varied between 1.25 and 15, and the working distance was 101 mm. The image intensifier had a maximum gain of 5 106 and was sensitive to visible light. The EM-CCD camera had 512 512 light sensitive pixels, which were each 16 16 lm in size and had a maximum linear gain of 8 105 electrons. The system had a spatial resolution of 1 lm; the resolution of a single-ion hit. An ion beam of 15-MeV O accelerated by the tandem accelerator at JAEA/Takasaki was used for the sensitivity test of the system. The linear energy transfer of the beam was equivalent to that used in radiation studies of biological living cells. The samples were set in a holder in the center of the vacuum chamber, and the lens was set at a distance of 60 mm downstream of the sample gazing through a view port glass with a transmission of 92% for visible light (Fig. 1). All images were collected on a 16-bit gray-scale in TIF format. The Al2O3:Eu at a fluence of 3.0 1016 cm 2 annealed for 0.5 h at 600°C and ZnS:Ag were irradiated by a stationary beam area of 2.3 3.2 lm2. The number of incident ions were counted before irradiation using a silicon charged-particle detector. 3. Results and discussion Implantation fluence, annealing temperature and annealing time were adjusted to increase the PL intensity. PL measurements were carried out for the samples annealed for 1 h at 800°C to investigate the relationship between the implantation fluence and PL intensity. The PL intensity is seen to increase with increasing implantation fluence, with a maximum PL intensity at a fluence of 3.0 1016 cm 2, as shown in Fig. 2. PL was observed for wavelengths ranging from 570 to 730 nm. The peaks at 598, 620, 658 and 690 nm are attributed to inter-level transitions between the electronic energy levels of Eu3+ [9]. The Eu peak at 690 nm overlaps with the Cr3+ peak at 690 nm [10], which cannot be removed completely in the a-Al2O3 production process. The strongest Eu peak at 620 nm was used in the PL analysis. The dependence of the luminescence intensity on the annealing temperature was then investigated for the sample with an
3 × 1016 cm -2 3 × 1015 cm -2 3 × 1014 cm -2
400
500
600
700
800
900
Wavelength (nm) Fig. 2. Implantation fluence dependence of the PL intensity of Al2O3:Eu. The annealing temperature and annealing time of the samples were fixed at 800°C and 1 h, respectively. The samples implanted at 3.0 1016 cm 2 emits the maximum PL intensity.
Ion fluence: 3 × 10 16 cm -2 Annealing time: 1 h
PL Intensity (arb. units)
Fig. 1. Schematic drawing of the single-ion hit detection system and the setup for a sensitivity test.
PL Intensity (arb. units)
Annealing temperature: 800°C Annealing time: 1 h
600 °C 700 °C 500 °C 800 °C 900 °C
300
400
500
600
700
800
900
Wavelength (nm) Fig. 3. Annealing temperature dependence of the PL intensity of Al2O3:Eu. The implantation fluence and annealing time of the samples were fixed at 3.0 1016 cm 2 and 1 h, respectively. The 600°C-annealed sample emits the maximum PL intensity.
implantation fluence of 3.0 1016 cm 2. The highest PL peaks was observed at 590 nm form the sample annealed for 1 h at 600°C (Fig. 3). The PL spectra of the samples annealed below 700°C differ significantly from those annealed at temperatures above 800°C. A broad peak was observed with a maximum in the intensity at around 590 nm from the samples annealed below 700°C, while a sharp peak centered at 620 nm was observed from the samples annealed above 800°C. The spectra of Al2O3:Eu and Al2O3:Ar were both measured to identify the origin of the peaks in the PL spectra. The Al2O3:Ar samples had the same number of defects as the Al2O3:Eu samples. The Al2O3:Ar and Al2O3:Eu samples were annealed at 600°C for 0.5 h. No PL signal was observed for Al2O3:Ar, which confirmed that the luminescence peaks observed for Al2O3:Eu all originated from the implanted Eu ions. This may be attributed to the temperature-dependent behavior of Eu during annealing; diffusion is a major process at low temperatures and aggregation is significant at high temperatures. Since aggregated Eu do not contribute significantly to the luminescence [11], the selection of a 600°C anneal is appropriate for obtaining stronger PL or IL emission. The
Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090
A. Yokoyama et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
hit rate of 200 s 1 was measured with a silicon charged particle detector. An example of the observed scintillation is shown in Fig. 5, with the square indicating the irradiation area on the sample (the square defines an area of 60 60 pixels). Within this area, the 35 scintillation points that were counted using ImageJ software (National Institutes of Health, USA) included both ion hits and noise. The average ratio of noise points in the image was obtained at 0.0047 points/pixel. More than about 20 scintillation points were assigned to ion hits. This indicated that each scintillation point correspond to 10 ions on average. Scintillation was also observed from the ZnS:Ag powder scintillator by hitting a 30 lm particle with a single-15-MeV-O ion per second.
Annealing temperature : 600°C
PL Intensity (arb. units)
Ion fluence : 3 × 10 16 cm -2
3
0.5 h 1.0 h 1.5 h 2.0 h 0h
4. Conclusion
300
400
500
600
700
800
900
Wavelength (nm) Fig. 4. Annealing time dependence of the PL intensity of Al2O3:Eu. The implantation fluence and annealing temperature of the samples were fixed at 3.0 1016 cm 2 and 600°C, respectively. The 0.5-h-annealed sample emits the maximum PL intensity.
In this study, we have investigated the luminescence properties of Al2O3:Eu samples to obtain a highly sensitive scintillator for the detection of single-ion hits in the megaelectron volt region. The maximum PL intensity was observed for the Al2O3:Eu sample with a total fluence of 3.0 1016 cm 2 annealed at 600°C for 0.5 h. The distribution layer of the doped Eu was 25 lm, as confirmed by Rutherford backscattering spectrometry. The results of the IL measurement using 15-MeV O show that the Al2O3:Eu scintillator and camera unit combination can be sufficiently sensitive for the realtime detection of a single-ion hit with a spatial resolution of 1 lm. Acknowledgment The authors would like to gratefully thank Dr. Miura in Graduate School of Engineering, Gunma University for PL measurement. This work was supported by a MEXT/JSPS Grant-in-Aid for Young Scientists (B) 23760837. References
100 µm
Fig. 5. Ion luminescence image from Al2O3:Eu with a total fluence of 3.0 1016 cm 2annealed for 0.5 at 600°C irradiated by 15-MeV O. The square defines a stationary beam irradiation area on the sample. A total of 200 ions/s were measured before irradiation using a silicon charged-particle detector. Within the square, there are about 35 scintillation points which were counted using ImageJ software (National Institutes of Health, USA), that include ion hits and and noise. More than about 20 of the points were assigned to ion hits.
dependence of the luminescence intensity on the annealing time was investigated for the sample with an implantation fluence of 3.0 1016 cm 2; the results are shown in Fig. 4. The intensity of the luminescence peak increases with decreasing annealing time, with a corresponding shift in the peak position from 545 nm to 620 nm. The result indicates that the best preparation conditions for obtaining the optimal PL intensity are annealed at 600°C for 0.5 h. The IL measurement to examine the sensitivity of the luminescence detection system was carried out by irradiating, with 15-MeV O, the sample had an implantation fluence of 3.0 1016 cm 2 and annealed at 600°C for 0.5 h. Before irradiation, a
[1] O. Veselov, W. Polak, R. Ugenskiene, K. Lebed, J. Lekki, Z. Stachura, J. Styczen, Development of the IFJ single ion hit facility for cell irradiation, Radiat. Prot. Dosimetry. 122 (2006) 316–319. [2] C. Shao, Y. Furusawa, Y. Kobayashi, T. Funayama, Involvement of gap junctional intercellular communication in the bystander effect induced by broad-beam or microbeam heavy ions, Nucl. Instr. Meth. Phys. Res. B 251 (2006) 177–181. [3] Y. Kobayashi, T. Funayama, S. Wada, M. Taguchi, H. Watanabe, Irradiation of single mammalian cells with a precise number of energetic heavy ions – Applications of microbeams for studying cellular radiation response, Nucl. Instr. Meth. Phys. Res. B 210 (2003) 308–311. [4] S. Gerardi, G. Galeazzi, R. Cherubini, Single-ion microbeam as a tool for lowdose radiation effects investigations, J. Phys: Conf. Ser. 41 (2006) 282–287. [5] W.Y.T. Kamiya, Y. Kobayashi, M. Cholewa, M.S. Krochmal, G. Laken, I.D. Larsen, L. Fiddes, G. Pavkhill, K. Dowsey, Development of an automated single cell irradiation system combined with a high-energy heavy ion microbeam system, Nucl. Instr. Meth. Phys. Res. B 181 (2001) 27–31. [6] T. Funayama, S. Wada, Y. Yokota, K. Fukamoto, T. Sakashita, M. Taguchi, T. Kakizaki, N. Hamada, M. Suzuki, Y. Furusawa, H. Watanabe, K. Kiguchi, Y. Kobayashi, Heavy-ion microbeam system at JAEA-Takasaki for microbeam biology, J. Radiat. Res. 49 (2008) 71–82. [7] M.K.M. Iwaki, K. Aono, Ion beam induced luminescence of Tb-implanted sapphire, Nucl. Instr. Meth. Phys. Res. B 127 (1997) 488–491. [8] M.I.K. Aono, Ion beam-induced luminescence of Eu-implanted Al2O3 and CaF2, Nucl. Instr. Meth. Phys. Res. B 141 (1998) 518–522. [9] M.G.A.-H.A.E. Esparza-Garci´a, M.A. Aguilar-Frutis, C. Falcony, Cathodoluminescent and photoluminescent properties of Al2O3 powders doped with Eu, Phys. Stat. Sol. (a) 193 (1) (2002) 117–124. 193 (2002) 117–124. [10] V.N. Makhov, A. Lushchik, C.B. Lushchik, M. Kirm, E. Vasil’chenko, S. Vielhauer, V.V. Harutunyan, E. Aleksanyan, Luminescence and radiation defects in electron-irradiated Al2O3 and Al2O3:Cr, Nucl. Instr. Meth. Phys. Res. B 266 (2008) 2949–2952. [11] P.D.T. N. Can, D. E. Hole and C. N. Afonso, High intensity luminescence from pulsed laser annealed europium implanted sapphire, Appl. Phys. Lett. 65 (15), 10 October 1994, 65 (1994) 1871–1873.
Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Development of real-time position detection system for single-ion hit A. Yokoyama a,⇑, W. Kada b, T. Satoh a, M. Koka a, S. Yamamoto a, T. Kamiya a, W. Yokota a a b
Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency (JAEA), 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japan Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-machi, Kiryu, Gunma 376-8515, Japan
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Single-ion Ion luminescence Real-time detection Photoluminescence
a b s t r a c t A real-time position detection system has been developed for a single-ion hit. The system is composed of a position sensitive camera unit and a luminescent scintillator. The camera unit includes 512 512 pixel electron-multiplier charge-coupled device, an image intensifier tube, and an object lens with a working distance of 101 mm. To obtain a highly sensitive luminescent scintillator for the detection of a single ion in the mega-electron-volt region, we investigate the photoluminescence properties of a-Al2O3 single-crystals implanted with Eu(Al2O3:Eu) at a fluence ranging from1014 to 1016 cm 2. The Al2O3:Eu samples were annealed at temperature from 500°C to 900°C. The results of 15-MeV O singleion hit experiments using Al2O3:Eu with a fluence of 3.0 1016 cm 2 annealed for 0.5 h at 600°C indicate that our system is sufficiently sensitive to detect the single-ion hit with a spatial resolution of 1 lm in real time. Ó 2014 Published by Elsevier B.V.
1. Introduction Real-time position detection of single ions is important for studying the microscopic irradiation of biological living cells [1–4]. The technology to shoot an ion at a target with a spatial accuracy of a few micrometers, called a single-ion hit, has been utilized at JAEA/Takasaki. The spatial accuracy of the single-ion hit at this facility is a few micrometers at energies of a few to hundreds of mega-electron-volt. A CR-39 plastic track detector placed under the sample is currently used to detect the position of the ions hitting the sample [5]. The CR-39 detector is made of polymerized diethyleneglycol bis allylcarbonate. The ion tracks formed in the CR-39 are observed off-line using a microscope after chemical etching [6]. Real-time position detection of the single-ion hit would provide a significant advance for the microscopic irradiation of biological cells. The detection of luminescence induced by a single ion using a ZnS:Ag powder scintillator was tested, but position resolution was insufficient because light scattering occurs around the grain boundaries in the powders and the incident ions deflect with getting into the sample. The aim of this study is to establish a position detection system for a single-ion hit using the strong ion luminescence (IL) emitted by Al2O3:Eu and a highly sensitive camera unit. Among single-crystal scintillators implanted with rare-earth ions, Al2O3:Eu (Eu is ⇑ Corresponding author. Tel.: +81 (0)27 346 9634. E-mail address: [email protected] (A. Yokoyama).
implanted into a-Al2O3 as activator), is of particular interest because of its strong luminescence under electron and ion beam irradiation [7,8]. Ion implantation is a good method for forming luminescence layer with nanometer-order in the sample for a high spatial resolution. The detection system described here is more sensitive than equivalent commercially available devices and includes image intensifier tubes, which have a maximum gain of 5 106 lm=m2 =lx, and electron-multiplier charge-coupled device (EM-CCD) camera, which have a maximum linear gain of 8 105 electrons. 2. Experimental Al2O3:Eu was prepared using ion implantation technique; mirror polished c-plane a-Al2O3 plates with a size of 10 10 mm2 and a thickness of 300 lm were used as the starting material. Ion implantation was carried out using the 400 kV ion implanter at JAEA/Takasaki and 350, 250 and 150-keV Eu ion were implanted in the same a-Al2O3 sample. The total Eu implantation fluence was varied between 3.0 1014 and 3.0 1016 cm 2. The Eu beam current was kept below 1.0 lA/cm2. To investigate the effect of defects caused by the Eu implantation on the luminescence of Al2O3:Eu, the Al2O3 samples were irradiated by 120, 80 and 50-keV Ar beam. The Ar beam was selected to form defects that did not contribute to scintillation. The Al2O3:Eu samples were annealed in an electric furnace, and the annealing temperature and annealing time were varied from 500 to 1000°C and 0 to 2.0 h, respectively.
http://dx.doi.org/10.1016/j.nimb.2014.02.090 0168-583X/Ó 2014 Published by Elsevier B.V.
Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090
2
A. Yokoyama et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
The luminescence of the Al2O3:Eu samples was characterized using photoluminescence (PL) measurements. Both PL and IL occur via the same electric excitation mechanisms. The PL measurements were carried out at room temperature using a 325-nm, 20-mW HeCd laser with 0.5-mm-diameter spot size. The PL of the Al2O3:Eu samples was detected using a high-sensitivity spectrometer and an electrically-cooled CCD camera. The pixel array of the camera was 1340 100 pixels and the pixel size was 20 20 lm. A lowcut filter was placed in front of the spectrometer to cut off the excitation wavelength of 325 nm. The IL detection system is required to have a spatial resolution of approximately 1 lm, the same as the spatial accuracy of the single-ion hit. The detection system consisted of a long-workingdistance lens, a zoom lens tube, an image intensifier with two micro-channel plates and EM-CCD camera, as shown in Fig. 1. The long-working distance lens and zoom lens tube had optical magnifications that could be varied between 1.25 and 15, and the working distance was 101 mm. The image intensifier had a maximum gain of 5 106 and was sensitive to visible light. The EM-CCD camera had 512 512 light sensitive pixels, which were each 16 16 lm in size and had a maximum linear gain of 8 105 electrons. The system had a spatial resolution of 1 lm; the resolution of a single-ion hit. An ion beam of 15-MeV O accelerated by the tandem accelerator at JAEA/Takasaki was used for the sensitivity test of the system. The linear energy transfer of the beam was equivalent to that used in radiation studies of biological living cells. The samples were set in a holder in the center of the vacuum chamber, and the lens was set at a distance of 60 mm downstream of the sample gazing through a view port glass with a transmission of 92% for visible light (Fig. 1). All images were collected on a 16-bit gray-scale in TIF format. The Al2O3:Eu at a fluence of 3.0 1016 cm 2 annealed for 0.5 h at 600°C and ZnS:Ag were irradiated by a stationary beam area of 2.3 3.2 lm2. The number of incident ions were counted before irradiation using a silicon charged-particle detector. 3. Results and discussion Implantation fluence, annealing temperature and annealing time were adjusted to increase the PL intensity. PL measurements were carried out for the samples annealed for 1 h at 800°C to investigate the relationship between the implantation fluence and PL intensity. The PL intensity is seen to increase with increasing implantation fluence, with a maximum PL intensity at a fluence of 3.0 1016 cm 2, as shown in Fig. 2. PL was observed for wavelengths ranging from 570 to 730 nm. The peaks at 598, 620, 658 and 690 nm are attributed to inter-level transitions between the electronic energy levels of Eu3+ [9]. The Eu peak at 690 nm overlaps with the Cr3+ peak at 690 nm [10], which cannot be removed completely in the a-Al2O3 production process. The strongest Eu peak at 620 nm was used in the PL analysis. The dependence of the luminescence intensity on the annealing temperature was then investigated for the sample with an
3 × 1016 cm -2 3 × 1015 cm -2 3 × 1014 cm -2
400
500
600
700
800
900
Wavelength (nm) Fig. 2. Implantation fluence dependence of the PL intensity of Al2O3:Eu. The annealing temperature and annealing time of the samples were fixed at 800°C and 1 h, respectively. The samples implanted at 3.0 1016 cm 2 emits the maximum PL intensity.
Ion fluence: 3 × 10 16 cm -2 Annealing time: 1 h
PL Intensity (arb. units)
Fig. 1. Schematic drawing of the single-ion hit detection system and the setup for a sensitivity test.
PL Intensity (arb. units)
Annealing temperature: 800°C Annealing time: 1 h
600 °C 700 °C 500 °C 800 °C 900 °C
300
400
500
600
700
800
900
Wavelength (nm) Fig. 3. Annealing temperature dependence of the PL intensity of Al2O3:Eu. The implantation fluence and annealing time of the samples were fixed at 3.0 1016 cm 2 and 1 h, respectively. The 600°C-annealed sample emits the maximum PL intensity.
implantation fluence of 3.0 1016 cm 2. The highest PL peaks was observed at 590 nm form the sample annealed for 1 h at 600°C (Fig. 3). The PL spectra of the samples annealed below 700°C differ significantly from those annealed at temperatures above 800°C. A broad peak was observed with a maximum in the intensity at around 590 nm from the samples annealed below 700°C, while a sharp peak centered at 620 nm was observed from the samples annealed above 800°C. The spectra of Al2O3:Eu and Al2O3:Ar were both measured to identify the origin of the peaks in the PL spectra. The Al2O3:Ar samples had the same number of defects as the Al2O3:Eu samples. The Al2O3:Ar and Al2O3:Eu samples were annealed at 600°C for 0.5 h. No PL signal was observed for Al2O3:Ar, which confirmed that the luminescence peaks observed for Al2O3:Eu all originated from the implanted Eu ions. This may be attributed to the temperature-dependent behavior of Eu during annealing; diffusion is a major process at low temperatures and aggregation is significant at high temperatures. Since aggregated Eu do not contribute significantly to the luminescence [11], the selection of a 600°C anneal is appropriate for obtaining stronger PL or IL emission. The
Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090
A. Yokoyama et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
hit rate of 200 s 1 was measured with a silicon charged particle detector. An example of the observed scintillation is shown in Fig. 5, with the square indicating the irradiation area on the sample (the square defines an area of 60 60 pixels). Within this area, the 35 scintillation points that were counted using ImageJ software (National Institutes of Health, USA) included both ion hits and noise. The average ratio of noise points in the image was obtained at 0.0047 points/pixel. More than about 20 scintillation points were assigned to ion hits. This indicated that each scintillation point correspond to 10 ions on average. Scintillation was also observed from the ZnS:Ag powder scintillator by hitting a 30 lm particle with a single-15-MeV-O ion per second.
Annealing temperature : 600°C
PL Intensity (arb. units)
Ion fluence : 3 × 10 16 cm -2
3
0.5 h 1.0 h 1.5 h 2.0 h 0h
4. Conclusion
300
400
500
600
700
800
900
Wavelength (nm) Fig. 4. Annealing time dependence of the PL intensity of Al2O3:Eu. The implantation fluence and annealing temperature of the samples were fixed at 3.0 1016 cm 2 and 600°C, respectively. The 0.5-h-annealed sample emits the maximum PL intensity.
In this study, we have investigated the luminescence properties of Al2O3:Eu samples to obtain a highly sensitive scintillator for the detection of single-ion hits in the megaelectron volt region. The maximum PL intensity was observed for the Al2O3:Eu sample with a total fluence of 3.0 1016 cm 2 annealed at 600°C for 0.5 h. The distribution layer of the doped Eu was 25 lm, as confirmed by Rutherford backscattering spectrometry. The results of the IL measurement using 15-MeV O show that the Al2O3:Eu scintillator and camera unit combination can be sufficiently sensitive for the realtime detection of a single-ion hit with a spatial resolution of 1 lm. Acknowledgment The authors would like to gratefully thank Dr. Miura in Graduate School of Engineering, Gunma University for PL measurement. This work was supported by a MEXT/JSPS Grant-in-Aid for Young Scientists (B) 23760837. References
100 µm
Fig. 5. Ion luminescence image from Al2O3:Eu with a total fluence of 3.0 1016 cm 2annealed for 0.5 at 600°C irradiated by 15-MeV O. The square defines a stationary beam irradiation area on the sample. A total of 200 ions/s were measured before irradiation using a silicon charged-particle detector. Within the square, there are about 35 scintillation points which were counted using ImageJ software (National Institutes of Health, USA), that include ion hits and and noise. More than about 20 of the points were assigned to ion hits.
dependence of the luminescence intensity on the annealing time was investigated for the sample with an implantation fluence of 3.0 1016 cm 2; the results are shown in Fig. 4. The intensity of the luminescence peak increases with decreasing annealing time, with a corresponding shift in the peak position from 545 nm to 620 nm. The result indicates that the best preparation conditions for obtaining the optimal PL intensity are annealed at 600°C for 0.5 h. The IL measurement to examine the sensitivity of the luminescence detection system was carried out by irradiating, with 15-MeV O, the sample had an implantation fluence of 3.0 1016 cm 2 and annealed at 600°C for 0.5 h. Before irradiation, a
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Please cite this article in press as: A. Yokoyama et al., Development of real-time position detection system for single-ion hit, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.090