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Article type: Cover
2008 Volume 35 Issue 2 Pages
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Article type: Index
2008 Volume 35 Issue 2 Pages
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Article type: Index
2008 Volume 35 Issue 2 Pages
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Article type: Index
2008 Volume 35 Issue 2 Pages
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Article type: Index
2008 Volume 35 Issue 2 Pages
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Hiraku Ogino, Masahito Watanabe
Article type: Article
2008 Volume 35 Issue 2 Pages
73-
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Satoshi Uda, Xinming Huang
Article type: Article
2008 Volume 35 Issue 2 Pages
74-80
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The crystal growth of YBCO (123:YBa_2Cu_3O_<7-x>) superconductive oxide under an external electric field has been investigated by means of in-situ observations and differential thermal analysis. The growth process of YBCO crystal via a peritectic reaction, i.e., 211(Y_2BaCuO_5) + liquid → YBCO (123), is differentiated into (1) dissolution of the 211 phase into solution, (2) transportation process of the solute, Y(Y_2O_3), in the liquid, (3) nucleation and (4) kinetic attachment of the solute to the growth front. Each process was modified by an external electric field of 600 V/cm which turned into an electric field as large as 10^4 to 10^5 V/cm occurring in an electric double layer forming at the solid-solution interface ; however, almost no electric field could be generated in the bulk liquid due to it being electrically conductive. The external electric field enhanced dissolution of the 211 gains, but had almost no effective electric field operated on the transportation process of the solute, and little effect was observed on the solute attachment kinetics. On the other hand, the external electric field increased the critical energy for the nucleation of the YBCO grains, which retarded the nucleation of the YBCO grains.
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Hiraku Ogino, Akira Yoshikawa, Martin Nikl
Article type: Article
2008 Volume 35 Issue 2 Pages
81-88
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Single crystal scintillators are used to detect high-energy radiation ray. In several scintillator materials, scintillation performances are limited by point defect such as oxygen deficiency and cation antisite through formation of color center, decrease of scintillation light yield and slow down of scintillation decay. Y_3Al_5O_<12> and Lu_3Al_5O_<12> systems, melt grown crystals contains Re-Al antisite type cation defects, which RE ions residing at octahedral Al site. This defect makes shallow electron trap and slow down scintillation process greatly in Ce:LuAG, as a result major part of the emission occur around μs〜ms order time scale. Such point defects and are regarded inevitable and scintillation properties degraded by the defect are considered as substantial properties of the material. But changing trap depth through chemical substitution, this situation could be improved. In this paper the effect of substitution of Al site by Ga of the LuAG based scintillator are reported.
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Akira Yoshikawa, Takayuki Yanagida, Yuui Yokota, Hiraku Ogino
Article type: Article
2008 Volume 35 Issue 2 Pages
89-95
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On the study to develop novel scintillator crystal, they focus mainly on selection of emission center and host lattice. However, for the practical use as radiation detector or medical imaging system, arraying and assembling technology is required. Only after those processes, the two dimensional imaging is obtained. In this report, we report on the design rule of novel scintillator crystal as well as the way toward the two dimensional imaging.
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Masanori Koshimizu, Kengo Shibuya, Keisuke Asai
Article type: Article
2008 Volume 35 Issue 2 Pages
96-103
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We have been developing novel scintillating materials using quantum confinement effects in semiconductor nanostructures. It has been well known that the quantum confinement effects in semiconductor nanostructures enhance the luminescence quantum efficiency and the radiative decay rate of excitons. Thus far, many research groups have fabricated various types of light-emitting semiconductor nanostructures however, their application to scintillating materials has not yet been investigated. Our group is the first to apply these low-dimensional systems for radiation detection. In the present paper, we describe the advantages of the application of semiconductor nanostructures to scintillating materials, as well as the difficulties involved in constructing single crystals comprising semiconductor nanostructures suitable for scintillating materials. We introduce two successful examples of scintillating materials based on semiconductor nanostructures, i.e., self-organized multiple quantum-well structures in organicinorganic hybrid perovskite-type materials and semiconductor nanocrystals as precipitates of impurity compounds in cesium halide crystals.
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Yoshiyuki Usuki, Kei Kamada, Kosuke Tsutsumi, Chisato Suzuki, Tomoharu ...
Article type: Article
2008 Volume 35 Issue 2 Pages
104-110
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Pr:LuAG[(Pr_xLu_<1-x>)_3Al_5O_<12>] has an advantage on very fast emission decay time due to 5d-4f transition of Pr^<3+>. Recently we have developed 2-inch-diameter Pr:LuAG single crystal and measured various scintillation properties of grown crystals. In this work, we obtained the following result; the segregation coefficient of Pr is found to be about 0.062 and 2-inch-diameter crystals are obtained with the solidification fraction of about 0.4 from the melt with the initial concentration of 2.5 at % Pr. The light output of Pr:LuAG single crystal is about three times higher than that in BGO at room temperature. The two emission peaks are found at around 310 and 375 nm by UV excitation. The luminescence decay time is as fast as 21ns and its rise time is as short as 400 ps by pulse X-ray excitation. The optical transmittance without AR coating is about 70% at 310 nm. The light output at 373 K is about 50% higher than that at room temperature.
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Hiroyuki Ishibashi
Article type: Article
2008 Volume 35 Issue 2 Pages
111-117
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Positron emission tomography(PET), a medical imaging equipment capable of detecting a tiny tumor such as that of cancer, is rapidly spreading as a common clinical tool. Detection efficiency for the gamma-rays with an energy of 511 keV is one of the most important issues for the improvement of PET. GSO single crystal, which was first reported by Takagi and Fukazawa, provides an optimum balance of all scintillation characteristics and is being used as gamma-ray detectors in the PET equipment. To apply the GS0 crystals as PET detectors, we have developed a crystal growth technology and have enlarged the size of the crystal. A review is made in this paper on the requirements of scintillation crystals for PET equipment after an introduction on the principle of PET and its gamma-ray detectors. Next generation PET and prospects for some new scintillation crystals are also described.
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Keitaro Hitomi, Yohei Kikuchi, Tadayoshi Shoji, Keizo Ishii
Article type: Article
2008 Volume 35 Issue 2 Pages
118-122
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Thallium bromide(TlBr) is a compound semiconductor with band-gap energy of 2.68eV. High photon stopping power is one of the most attractive physical properties of TlBr, originating from its high density (7.56g/cm^3) and high atomic numbers of the constituent elements (Tl and Br). Thus, TlBr is a promising semiconductor material for fabrication of gamma-ray spectrometers operating at room temperature. The T1Br crystals grown by the traveling molten zone method have exhibited the charge transport properties comparable to commercially available gamma-ray detector grade CdTe crystals. A TlBr detector with small pixels has exhibited an energy resolution of approximately 1% for 662keV gamma-rays at room temperature. Significant suppression of polarization phenomena in TlBr detectors has been achieved by adopting Tl metal as the electrode material for TlBr detectors. By changing the polarity of the applied bias voltages every 24 hours, the TlBr detectors with Tl electrode have exhibited stable spectroscopic performance for 600 hours.
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Shinjiroh Hara, Ryuji Katayama
Article type: Article
2008 Volume 35 Issue 2 Pages
123-125
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[in Japanese]
Article type: Article
2008 Volume 35 Issue 2 Pages
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[in Japanese]
Article type: Article
2008 Volume 35 Issue 2 Pages
126-127
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[in Japanese]
Article type: Article
2008 Volume 35 Issue 2 Pages
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[in Japanese]
Article type: Article
2008 Volume 35 Issue 2 Pages
127-128
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[in Japanese]
Article type: Article
2008 Volume 35 Issue 2 Pages
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Hiroshi Fujioka
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2008 Volume 35 Issue 2 Pages
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Katsuo Tsukamoto
Article type: Article
2008 Volume 35 Issue 2 Pages
130-131
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tomoya Ogawa
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2008 Volume 35 Issue 2 Pages
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Article type: Appendix
2008 Volume 35 Issue 2 Pages
133-134
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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2008 Volume 35 Issue 2 Pages
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Article type: Appendix
2008 Volume 35 Issue 2 Pages
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