Faculty Profiles - URITANI Akira

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Feasible Study on Energy Subtraction X-Ray CT Technique Using Comb-Shape Filtered X-Rays International conference

T. Tsubouchi, K. Watanabe, A. Yamazaki, A. Uritani

2011 IEEE Nuclear Science Symposium

Event date： 2011.10

Language：English Presentation type：Poster presentation

Country：Spain

X-ray CT can acquire high quality tomograms and can be used for various diagnoses including early detection of cancers. Since radiation exposure in X-ray CT cannot be negligible, reduction of radiation exposure is quite important for frequent diagnosis. To reduce the radiation exposure, we are developing the novel X-ray CT technique, which can acquire high contrast images. Utilizing the energy information of X-rays as the energy subtraction method is useful to improve the image contrast because each material has different energy dependences on interactions with X-ray. To utilize the energy information of X-rays, we attempt to use the filtered X-rays as X-ray sources with different energy spectra. Especially we propose utilizing a comb-shape filter to simultaneously acquire transmission images by filtered and unfiltered X-rays. The radiation exposure can be expected to be reduced by placing the comb-shape filter between an X-ray source and an object. In this paper, we study the feasibility of the proposed CT technique through simulations and basic experiments. To demonstrate the advantage of the proposed CT technique, simulation studies were carried out. In these simulations, transmission images were derived based on an exponential attenuation law. The transmission images through a comb-shape filter have a striped structure. By estimating the X-ray intensities at intermediate points of discrete data points with the interpolation method, we can simultaneously acquire two transmission images obtained by filtered and unfiltered X-rays. From the transmission images obtained in simulations, we reconstructed an image by using the energy subtraction method. We confirm that the contrast of the images can be improved by applying the energy subtraction method using comb-shape filtered X-rays. In addition, we confirm the advantage of the proposed method through basic experiments.

Optical and Scintillation Properties of Pure, Cu-, and Zn-Doped LiAlO₂ Single Crystals International conference

Y. Fujimoto, T. Yanagida, Y. Yokota, N. Kawaguchi, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, A. Uritani, T. Iguchi, A. Yoshikawa

2011 IEEE Nuclear Science Symposium

Event date： 2011.10

Language：English Presentation type：Poster presentation

Country：Spain

Most common thermal neutron detector with high stopping power is 3He gas counter. However, unfortunately, 3He gas supply crisis became serious in recent years. By these reasons, development of alternative detector such as transparent bulk crystalline scintillator coupled with suitable photo-detector is strongly required. It is well known that 6Li isotope has high cross section (~ 940 barn) to thermal neutrons and convert them into ionizing particles according to the 6Li(n, α)t reaction. Here, a new class of scintillators for thermal neutron detection, based on lithium aluminate LiAlO2 crystals, is described. LiAlO2 crystal contain large amount of 6Li, and its low efficiency for background gamma-ray due to low density (2.75 g/cm3). In our study, some kind of element (Cu2+, Zn2+, Na+)-doped crystalline scintillators have been grown by micro-pulling down (μ-PD) technique. After cutting and polishing, optical characteristics and scintillation properties of the crystals were examined. Transmission spectra of polished crystals were evaluated with JASCO V550 spectrometer in 190-900 nm wavelength ranges. In the evaluations of scintillation characterization, 241 Am 5.5 MeV α-ray excited radioluminescence spectrums and its decay curve were measured. The crystal showed broad intense emission band around 300-400 nm under α-ray excitation, possibility due to an intrinsic origin. The scintillation decay time was calculated to be about 2.6 μs. Throughout the study, we investigate scintillation properties of pure and doped LiAlO2 crystals, systematically.

Neutron-Gamma Discrimination in a Ce:LiCaAlF₆ Scintillator Based on Pulse Shape Discrimination Using Digital Signal Processing International conference

K. Watanabe, Y. Kondo, A. Yamazaki, A. Uritani, T. Iguchi, N. Kawaguchi, T. Yanagida, Y. Fujimoto, Y. Yokota, K. Kamada, K. Fukuda, T. Suyama, A. Yoshikawa

2011 IEEE Nuclear Science Symposium

Event date： 2011.10

Language：English Presentation type：Poster presentation

Country：Spain

Neutron detection techniques play an important role in various fields. As one of the promising candidates of neutron detectors with high efficiency, rare-earth-ion-doped LiCaAlF6 (LiCAF) scintillators have been developed. Since the LiCAF scintillator consists of light elements, it has low gamma-ray sensitivity. A large single crystal of a LiCAF up to a few inches diameter can be fabricated with Czochralski technique. The large LiCAF scintillator can be a promising epi-thermal neutron detector with high detection efficiency. When using a large crystal, we must consider the influence of gamma rays because neutron fields are usually accompanied by high-energy prompt gamma rays. A Ce:LiCAF scintillator can discriminate neutron and gamma-ray events with a pulse shape discrimination based on a difference in scintillation decay time. In this paper, we adopt the digital signal processing technique to investigate the detailed properties of the scintillation decay time and evaluate the performance of neutron-gamma discrimination. A Ce:LiCAF scintillator has quite fast component about 1 ns only for fast electrons produced by gamma-rays. There is no fast component for heavy charged particles produced by neutron captures. We, therefore, can discriminate the neutron and gamma-ray events by presence of this fast component. The responses of Ce:LiCAF scintillators were investigated through basic experiments using a Cf-252 neutron source with a polyethylene moderator and a Co-60 gamma-ray source. By using the pulse shape discrimination based on the presence of fast component, the gamma-ray sensitivity can be reduced to 1/10 of that without the pulse shape discrimination under condition keeping the 90% neutron sensitivity. In addition, we preliminarily evaluate the gamma-ray rejection performance for various Ce content LiCAF crystals. In these evaluations, low Ce content samples showed high gamma-ray rejection property.

Development of a Micro-Size Dosimeter Using an Optical Fiber Probe and a Photostimulable Storage Phosphor International conference

A. Yamazaki, K. Watanabe, K. Nakahashi, H. Miyamae, A. Uritani, E. Ariga

2011 IEEE Nuclear Science Symposium

Event date： 2011.10

Language：English Presentation type：Poster presentation

Country：Spain

Radiotherapy is one of the most effective treatments for cancer. Radiotherapy treatments are carefully planned to maximize the effectiveness of treatments and to suppress the unwanted radiation dose. However, practical doses in the patients body during treatments are almost never monitored because the present dose monitor is too large to insert into the affected area in the body. Therefore, development of a small size and on-line dosimeter is required. The sensitivity of the radiation detector generally decrease with downsizing the detector. When downsizing the detector sensitive volume, the signal intensity decreases as compared with the noise causing in the signal line. When using small detector of the successive signal readout type, we suffer from low signal to noise ratio. On the other hand, the integrating-type detector can obtain larger signals than a noise level even if the size is smaller than the charged particle range, because small energy depositions can be accumulated in the detector until exceeding a noise level. We propose a novel micro-size dosimeter using an optical fiber probe and a photostimulabe storage phosphor (PSP) such as BaFBr:Eu2+, which is one of the integrating type detector elements. Through basic experiments using the prototype dosimeter, the feasibility of the proposed dose monitoring method has been confirmed. We confirm that increasing the stimulus laser power is effective to improve the signal to noise ratio. The lower limit of detectable dose of the prototype dosimeter probe having sensitive region with the diameter of 400 μm is preliminarily estimated to be 1.4 mGy for a Co-60 gamma-rays. This value is much smaller than the typical irradiation dose (a few Gy per treatment) in the radiotherapy. We can measure the dose in a few hundred subdivisions during a treatment. We, therefore, conclude that the proposed micro-size dosimeter can be a promising candidate of in-vivo and on-line dose monitor in the radiotherapy.

ヘリカル型核融合実験装置における中性子モニタリングシステムその２

西尾直人, 山崎敦, 渡辺賢一, 瓜谷章,磯部光孝, 山西弘城

日本原子力学会 2011年秋の大会

レーザー吸収分光に基づくナトリウム漏洩検出器の開発その2

小倉智志, 瓜谷章, 渡辺賢一, 山崎淳,富田英生, 伊藤主税

日本原子力学会 2011年秋の大会

櫛状フィルタを利用したエネルギー差分X 線CT に関する基礎研究

坪内俊郎, 渡辺賢一, 山崎淳, 瓜谷章

日本原子力学会 2011年秋の大会

高速中性子増感材を用いた平坦応答中性子検出器に関する研究

大塚準平, 瓜谷章, 渡辺賢一, 山﨑淳

日本原子力学会 2011年秋の大会

小型指向性中性子検出器による原子炉内中性子方向分布計測

丸山秀典，渡辺賢一，瓜谷　章，山﨑　淳，河口範明，福田健太郎，柳田健之，吉川　彰

2011年秋季第72回応用物理学会学術講演会

Ce:LiCaAlF₆シンチレータにおけるデジタル波形処理を用いた中性子/ガンマ線弁別性能の評価

近藤良行，山﨑　淳，渡辺賢一，瓜谷　章，井口哲夫，柳田健之，河口範明，藤本　裕，横田有為，鎌田　圭，福田健太郎，須山敏久，吉川　彰

2011年秋季第72回応用物理学会学術講演会

輝尽性蛍光体と光ファイバーを組み合わせたマイクロサイズ線量計の特性評価試験

渡辺賢一，中橋弘太郎，宮前英史，山﨑　淳，瓜谷　章，有賀英司

2011年秋季第72回応用物理学会学術講演会

レーザー励起支援誘導結合プラズマ質量分析法に関する基礎検討

所　俊之，渡辺賢一，瓜谷　章，富田英生，井口哲夫

2011年秋季第72回応用物理学会学術講演会

形状制御ターゲットを用いたレーザー駆動陽子線加速の性能向上に関する基礎検討

石部　健，山﨑　淳，渡辺賢一，瓜谷　章，井上龍夫

2011年秋季第72回応用物理学会学術講演会

ヘリカル型核融合実験装置の中性子モニタリングシステムに関する研究

西尾直人, 山崎敦, 渡辺賢一, 瓜谷章,磯部光孝, 山西弘城

日本原子力学会 2010年春の年会

中性子用LiCaAlF₆シンチレータにおける中性子／ガンマ線弁別

渡辺賢一, 近藤良行, 山﨑淳, 瓜谷章,井口哲夫, 柳田健之, 藤本裕, 横田有為,鎌田圭, 吉川彰, 河口範明,福田健太郎, 須山敏尚

日本原子力学会 2010年春の年会

中性子線源による速中性子フルエンス標準の国際比較

西山潤, 原野英樹, 松本哲郎, 増田明彦,工藤勝久, 瓜谷章,Hyeonseo Park, Jungho Kim,Kil-Oung Choi

日本原子力学会 2010年春の年会

輝尽性蛍光体と光ファイバーを組み合わせたマイクロサイズ線量計の開発

渡辺賢一，中橋弘太郎，宮前英史，山崎　淳，瓜谷　章，有賀英司

第58回応用物理学関係連合講演会

位置敏感型検出器を用いたロングカウンタ型平坦応答中性子検出器の開発

大塚準平，瓜谷　章，渡辺賢一，山崎　淳

第58回応用物理学関係連合講演会

第三世代コンプトン散乱X線CTによる電子密度分布の画像化法

増地亮太，渡辺賢一，山崎　淳，緒方良至，瓜谷　章

第58回応用物理学関係連合講演会

櫛状フィルタを設置したX線CTシステムの開発

坪内俊郎，渡辺賢一，山崎　淳，瓜谷　章

第58回応用物理学関係連合講演会

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