Kei Kamada

Tohoku University, Japan

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Publications (164)154.01 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Unidirectionally solidified rare-earth activated GdAlO3(GAP)/Al2O3 eutectic crystal with well-aligned fibrous structure exhibits excellent light guiding property and can be used as a scintillator plate for high-resolution X-ray imaging. In this paper, the microstructures and orientation relationships of the GAP/Al2O3 eutectic fibers were investigated. The regular GAP single crystal fibers with a hexagonally close-packed arrangement grew straight in the same direction along the solidification direction, and were embedded in a c -axis oriented Al2O3 single crystal matrix. The majority of GAP fibers had the orientation relationships of [0 1 0]GAP//[0 0 0 1]Al2O3 to the growth direction and (1 0 0)GAP//(1 1 2¯ 0)Al2O3 to the interface plane, while slight misorientation angle of both [0 1 0]GAP axis and (1 0 0)GAP plane were observed. In the GAP/Al2O3 interface boundary, the lattice misfit between the two phases was relieved by insertion of extra half-planes on the Al2O3 side.
    Journal of the European Ceramic Society 12/2014; 34(15):3849–3857. · 2.36 Impact Factor
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    ABSTRACT: Sr co-doped Ce:LiCaAlF6 [Ce:Li(Ca,Sr)AlF6] crystals with various Ca/Sr ratios were grown by a micro-pulling-down (μ-PD) method and effects of Sr co-doping on crystal structure, chemical composition, optical and scintillation properties for Ce:LiCaAlF6 crystals were investigated as a neutron scintillator. High transparent Ce2%:Li(Ca,Sr)AlF6 crystals with 2% and 5% Sr contents were obtained while Ce2%:Li(Ca,Sr)AlF6 crystals with 10% and 20% Sr contents included milky parts in the crystals. a- and c-axis lengths of Ce:Li(Ca,Sr)AlF6 phase systematically increased with an increase of Sr content. In addition to the emission at 284 and 308 nm from Ce3+ ion, emission peaks at 367 nm appeared by Sr co-doping.
    Optical Materials 10/2014; · 1.92 Impact Factor
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    ABSTRACT: Cr-doped (GdX Y1−X)3Al5O12 (X = 0, 0.25, 0.50) crystals prepared by the micro-pulling down method were investigated to develop a infra-red scintillator for implantable patient dosimeter in radiation therapy. In order to evaluate their optical and scintillation performance, the following properties were measured: (i) transmittance between ultra-violet and near-infra red region, (ii) photoluminescence spectra under Xe-lamp excitation, and (iii) X-ray excited radio-luminescence spectra. Cr:Y3Al5O12 and Cr:(Gd0.25 Y0.75)3Al5O12 crystals showed increased transmittance of 80%, while Cr:(Gd0.50 Y0.50)3Al5O12 had a lower transmittance of 40% due to its polycrystalline structure. In addition, all the Cr:(GdX Y1−X)3Al5O12 crystals showed sharp scintillation luminescence peaks ascribed to Cr3+ d–d transitions. Therefore, these results suggested that Cr:Y3Al5O12 and Cr:(Gd0.25 Y0.75)3Al5O12 crystals can be candidate materials for the dosimeter use.
    Optical Materials 10/2014; · 1.92 Impact Factor
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    ABSTRACT: Eu doped LiSrAlF6 (Eu:LiSAF) crystals with various Eu concentrations were grown by a micro-pulling-down (μ-PD) method and the effects of Eu concentration control on crystal growth and scintillation properties for Eu:LiSAF crystals were investigated as a neutron scintillator. As-grown Eu0.3%:LiSAF crystal had no visible inclusion while milky parts were observed in the crystals with higher Eu contents. The secondary phases with the chemical composition of EuF2 or EuF3 in the Eu:LiSAF matrix were observed for the crystals with high Eu contents while the secondary phase couldn’t be observed in the powder XRD patterns. In the radioluminescence spectra of Eu:LiSAF crystals under α-ray irradiation, emission peaks around 375 nm originated from 5d–4f transition of Eu2+ ion were observed. The light yields systematically increased with an increase of actual Eu contents in the crystals and the decay times were 1490–1620 ns.
    Optical Materials 10/2014; · 1.92 Impact Factor
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    ABSTRACT: Eu doped SrI2 (Eu:SrI2) single crystals with various Eu contents were grown by a modified micro-pulling-down (μ-PD) method and effects of Eu concentration on scintillation properties were investigated. Eu 1%, 5%, 7.5%, 10% and 15%:SrI2 single crystals were obtained and all as-grown crystals indicated high transparency without visible inclusion. Actual Eu contents in the grown crystals were almost same as nominal compositions. In the X-ray radioluminescence spectra, emission peaks around 435 nm were observed in all crystals. Eu7.5 mol%:SrI2 crystals indicated the highest light yield, 78,000 ph/MeV, and the smallest energy resolution, 3.7%.
    Optical Materials 10/2014; · 1.92 Impact Factor
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    ABSTRACT: Sc doped YyLu3−yAl5O12 (y = 0–1) single crystals were grown by the μ-PD method. EPMA techniques were employed to check their chemical composition. Luminescence characteristics were measured. Anti-site defect-related host emission was observed within 280–360 nm wavelength. The light yield was increasing with Y concentration and with an optimum for Sc2% concentration. The Sc 2% doped Y3Al5O12 showed the highest light yield value around 30,000 photon/MeV and 670 ns scintillation decay time using a photomultiplier detector (R7600U). Substitution effects of the Lu site and their influence on luminescence and scintillation properties were studied.
    Optical Materials 10/2014; · 1.92 Impact Factor
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    ABSTRACT: Low temperature thermoluminescence of GAGG:Ce and LuAG:Pr scintillator crystals has been studied by means of the Tmax-Tstop method. It is shown that the glow curves of both materials are superpositions of discrete glow peaks and broad bands due to quasi-continuous Gaussian distributions of trapping levels. A model function has been built and trap parameters have been evaluated.
    Journal of Luminescence 10/2014; 154:452-457. · 2.14 Impact Factor
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    ABSTRACT: In this paper we report the measurements of pulse height spectra, radioluminescence spectra at various temperatures between 10 and 325 K, and low temperature thermoluminescence glow curves of Gd3Al2Ga3O12:Ce. It is shown that the scintillation yield of the studied material correlates with the concentration of cerium and anti-correlates with the thermoluminescence intensity. However, regardless of the cerium content, the yield at room temperature is almost twice lower than below 180 K.
    Optical Materials 08/2014; 36(10):1665-1669. · 1.92 Impact Factor
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    ABSTRACT: Ce:Gd3(AlxGa1−x)5O12 (x=2.5/5 and 3/5, Ce:GAGG-2.5 and Ce:GAGG-3) crystals were grown by the Czochralski process in order to reduce cost of the starting materials as compared with conventional Ce:Gd3Al2Ga3O12 (Ce:GAGG-2) crystal which have high light output. Although perovskite phase was detected in Ce:GAGG-3, Ce:GAGG-2.5 had single-phase garnet structure. Solidification fraction for the Ce:GAGG-2.5 growth was 0.52. Optical properties including transmittance, emission, and excitation spectra of 30 samples cut from the Ce:GAGG-2.5 bulk ingot did not depend on their original position along the growth axis. These samples had light outputs of approximately 58,000±3000 photons/MeV. However, scintillation decay times varied from 140 to 200 ns and depended on the position clearly.
    04/2014;
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    ABSTRACT: Nd and Yb doped CaYAlO4 crystals have been grown by the micro-pulling down method. The segregation coefficient along the growth direction and the radial dopant distribution were measured by using electron probe micro-analysis (EPMA). The X-ray induced luminescence spectra in the spectral range from 300 to 1500 nm were measured: Nd and Yb doped CaYAlO4 showed intense peaks at 990 and 1045 nm, respectively. These crystals would be promising materials for near infrared emission scintillators.
    04/2014;
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    ABSTRACT: We have investigated the optical properties of 1 mol% Nd-doped SrBr2 crystal grown by the Bridgman technique for an X-ray scintillator application. We succeeded in obtaining a transparent crystal, whose X-ray diffraction was measured under dry condition because of its hygroscopic nature. Roughly, we estimated that 90% of this crystal dissolved within 300 min. under 25 °C and 65─70% humidity. Under excitation by 270 and 400 nm photons several emission peaks originating from 4F3/2 or 4Gi1→4Ii2 (i1=5/2 and 7/2 and i2=13/2, 11/2, and 9/2) transitions of Nd3+ were observed. 1 mol% Nd:SrBr2 had a maximum quantum yield of approximately 45%. Additional emission peaks were observed under X-ray excitation.
    04/2014;
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    ABSTRACT: Some pyrosilicate scintillators such as Ce:Gd2Si2O7 and Ce:Lu2Si2O7 have a good light output, and especially Ce:(Gd,La)2Si2O7 has an excellent light output of over 36,000 ph/MeV. In order to search novel scintilators, we have developed a pyrogermanate-based scintillation material (Ce0.01,Gd0.90,La0.09)2Ge2O7 using the floating zone method. Although the light output was decreased due to quenching, 5d─4f transition of Ce3+ was observed around 480 nm in photo- and radio-luminescence spectra. This emission wavelength was longer than that of (Ce0.01,Gd0.90,La0.09)2Si2O7 with an emission wavelength of 390 nm.
    04/2014;
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    ABSTRACT: Read out test of inorganic–organic hybrid scintillator; Pr:LuAG single crystal covered with plastic scintillator BC-499 is demonstrated. Emission peaks of the hybrid scintillator was observed around 430 nm, which suit to the sensitive wavelength of photomultiplier tube (PMT). The Pr:LuAG sample coated with BC-499 showed the better light output than the that of Pr:LuAG itself. Light output was increased up to 30% sing PMT (Hamamatsu R9800). Decay curve of the hybrid scintillator was also measured and successfully modeled. Corporation.
    Japanese Journal of Applied Physics 03/2014; 53(4S):04EH10. · 1.07 Impact Factor
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    ABSTRACT: Ba co-doped Ce:LiCaAlF6 [Ce:Li(Ca,Ba)AlF6] and LiCaAlF6 [Li(Ca,Ba)AlF6] crystals with various Ba concentrations were grown and their structures, optical and scintillation properties were investigated. As-grown Ce2%Ba1% and Ce2%Ba2%:Li(Ca,Ba)AlF6 crystals were high transparency in all parts while an end part of as-grown Ce2%Ba5%:Li(Ca,Ba)AlF6 crystal and all parts of as-grown Ba5%:Li(Ca,Ba)AlF6 crystal included milky parts which decreased transmittance. Ce:Li(Ca,Ba)AlF6 crystals indicated the emission peaks at 288 and 308 nm from which was attributable to the 5d-4f transition of Ce3+ ion in the radioluminescence spectra under α-ray irradiation. In the case of Ce1%Ba2%:Li(Ca,Ba)AlF6 crystal, light yield under thermal neutron irradiation were improved. Decay times of Ce:Ce:Li(Ca,Ba)AlF6 under thermal neutron irradiation systematically increased with an increase of Ba concentration.
    IEEE Transactions on Nuclear Science 01/2014; 61(1). · 1.22 Impact Factor
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    ABSTRACT: Functional possibilities of Pr:LuAG single crystal covered with plastic scintillators are demonstrated. Shift of luminescence wavelength of the hybrid scintillators towards the region of higher spectral sensitivity of photodetectors and radiation responses of the hybrid scintillators were investigated. The Pr:LuAG sample coated with bis-MSBPVD showed the better light output and energy resolution than the Pr:LuAG itself. Light output was increased up to 55% and energy resolution was also improved to 6.5%@662 keV using APD (Hamamatsu S8664-8220). In the case of MPPC (Hamamatsu S10362_33_050 3600 pixel-type), light output was increased up to 35% and energy resolution was also improved to 9.8%@662 keV. Decay curve of the Pr:LuAG sample coupled with the WLS was also measured and successfully modeled.
    IEEE Transactions on Nuclear Science 01/2014; 61(1). · 1.22 Impact Factor
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    ABSTRACT: A depth-of-interaction (DOI) detector is required for developing a high resolution and high sensitivity PET system. Ce-doped Gd3Al2Ga3O12 (GAGG fast: GAGG-F) is a promising scintillator for PET applications with high light output, no natural radioisotope and suitable light emission wavelength for semiconductor based photodetectors. However, no DOI detector based on pulse shape analysis with GAGG-F has been developed to date, due to the lack of appropriate scintillators of pairing. Recently a new variation of this scintillator with different Al/Ga ratios—Ce-doped Gd3Al2.6Ga2.4O12 (GAGG slow: GAGG-S), which has slower decay time was developed. The combination of GAGG-F and GAGG-S may allow us to realize high resolution DOI detectors based on pulse shape analysis. We developed and tested two GAGG phoswich DOI block detectors comprised of pixelated GAGG-F and GAGG-S scintillation crystals. One phoswich block detector comprised of 2×2×5 mm pixel that were assembled into a 5×5 matrix. The DOI block was optically coupled to a silicon photomultiplier (Si-PM) array (Hamamatsu MPPC S11064-050P) with a 2-mm thick light guide. The other phoswich block detector comprised of 0.5×0.5×5 mm (GAGG-F) and 0.5×0.5×6 mm3 (GAGG-S) pixels that were assembled into a 20×20 matrix. The DOI block was also optically coupled to the same Si-PM array with a 2-mm thick light guide. In the block detector of 2-mm crystal pixels (5×5 matrix), the 2-dimensional histogram revealed excellent separation with an average energy resolution of 14.1% for 662-keV gamma photons. The pulse shape spectrum displayed good separation with a peak-to-valley ratio of 8.7. In the block detector that used 0.5-mm crystal pixels (20×20 matrix), the 2-dimensional histogram also showed good separation with energy resolution of 27.5% for the 662-keV gamma photons. The pulse shape spectrum displayed good separation with a peak-to-valley ratio of 6.5. These results indicate that phoswich DOI detectors with the two types of GAGGs are promising for developing a high resolution PET system.
    01/2014; 767:289–295.
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    ABSTRACT: A novel digital PET scanner based on Time over Threshold method is developed. The positron emission tomography (PET) is composed of 144channel Ce:Gd3Al2Ga3O12 (GAGG)-Avaranche photodiode (APD) detector arrays individually coupled with custom designed Time over Threshold (ToT) application-specific integrated circuit (ASIC) to realize the high count rate and good spatial resolution. Such an imaging system provides a simple front-end circuit and flexible digital signal processing like multiplexing such as a pulse train method. The measured energy resolution of the detector system was 6.7% for the 511 keV peak, and 4.25 ns time resolution was measured with a single detector module. The measured spatial resolution for a point source was 1.37 mm FWHM for our initial data with a columnar 22Na source.
    IEEE Transactions on Nuclear Science 01/2014; 61(1):348-352. · 1.22 Impact Factor
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    ABSTRACT: The scintillation properties of Gd3Al2Ga3O12:Ce3+ (GAGG:Ce) single crystals grown by the Czochralski method with 1 at% cerium in the melt were investigated and results were compared with so far published results in the literature. The light yield (LY) and energy resolution were measured using a XP5200B photomultiplier. Despite about twice higher LY for GAGG:Ce, the energy resolution is only slightly better than that of LuAG:Ce due to its worse intrinsic resolution and non-proportionality of LY. The LY dependences on the sample thickness and amplifier shaping time were measured. The estimated photofraction in pulse height spectra of 320 and 662 keV γ-rays and the total mass attenuation coefficient at 662 keV γ-rays were also determined and compared with the theoretical ones calculated using the WinXCom program.
    01/2014; 751:1–5.
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    ABSTRACT: Optical, scintillation and luminescent properties of 0.1 % Ti-, Mn- and Cu- doped lithium aluminate LiAlO2 crystals are studied. The crystals were grown by micro-pulling down (μ-PD) method under N2 + O2 (2 vol %) atmosphere. By the X-ray excitation, the crystals exhibited intense emission bands at ultraviolet-visible regions which can be attributed to the Ti4+-O2- charge transfer transition at 380 nm, 4T1→6A1 transition of Mn2+ ion at 550 nm and 3d94s-3d10 transition of Cu+ at 360 nm, respectively. The scintillation decay time were estimated to be about 1.8 and 9.9 μs for Ti 0.1 %, 310 μs and 2240 μs for Mn 0.1 %, and 3.6 μs and 19.6 μs for Cu 0.1 %. When 252Cf neutron irradiated the crystals, the relative scintillation light output found to be approximately (135 ± 13) × 102 ph/n (for Ti 0.1 %) and (87 ± 8.0) × 102 ph/n (for Cu 0.1 %) compared to that of GS20 commercial scintillator. Both TL and OSL spectra showed emission bands caused by the recombines of trapped electrons at the anion centers through the Ti4+, Mn2+ and Cu+ luminescence centers. The irradiation dose response was linear in the studied dose range at 0.1-5 Gy and 0.1-10 Gy.
    Radiation Measurements. 01/2014;

Publication Stats

404 Citations
154.01 Total Impact Points

Institutions

  • 2005–2014
    • Tohoku University
      • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      Japan
  • 2010
    • Osaka University
      • Institute of Laser Engineering
      Ōsaka-shi, Osaka-fu, Japan
    • Tokai University
      • Department of Chemistry
      Hiratsuka, Kanagawa-ken, Japan
  • 2008
    • Delft University of Technology
      Delft, South Holland, Netherlands