研究者詳細 - 瓜谷　章

講演・口頭発表等 - 瓜谷　章

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コンクリート内部を可視化する高エネルギー後方散乱X線イメージング装置の開発

豊川弘之, 藤原健,萬代新一,伊佐英範,瓜谷章, 渡辺賢一, 山崎淳, 遠山貴之

第10回放射線による非破壊評価シンポジウム　

開催年月日： 2016年2月

記述言語：日本語会議種別：口頭発表（一般）

開催地：東京都立産業技術研究センター　青海本部国名：日本国

後方散乱X線イメージングは、X線透過試験が適用できない複雑な形状の構造物や、足場の悪い現場、内部構造が不明の建造物でも、片側からのアクセスで内部を可視化することができる。そのため、現場での検査の効率化と高精度化が期待できる。我々は電子加速器技術を用いた高エネルギーX線発生装置と、一次元マルチスリットX線検出器を用いた後方散乱イメージングシステムを合わせて開発している。開発状況について報告する。

Pulsed neutron Bragg-edge transmission analysis of steel materials with different carbon content for applied research of iron cultural heritages 国際会議

M. Isono, M. Tanaka, Y. Shiota, K. Watanabe, Y. Kiyanagi and A. Uritani

15th Japan-Korea meeting on Neutron Science

開催年月日： 2016年1月

記述言語：英語会議種別：ポスター発表

国名：日本国

Detailed information such as raw materials, manufacturing techniques, material properties, producing areas and so on is still unclear concerning iron cultural heritage like Japanese sword and matchlock gun. Optical microscope, X-ray diffraction, EBSD and SEM have been used to get surface metallurgical information and to clarify their material characteristics. Most of the time, destruction of the sample is required for those analysis. However, non-destructive analysis is desired for the study of iron cultural heritage to keep their original shape and value.
Neutron has a high penetrating power for materials. So, by using neutron, it is possible to measure material characteristics of the inside of metal materials nondestructively. Pulsed neutron transmission spectroscopy is a new method and it's getting clear that an image indicating strain, crystallite size, crystalline orientation, crystal phase fraction, density of the material can be obtained by using the TOF energy analysis at a pulsed neutron source.
Four different carbon content steels of S25C (about 0.25mass%C), S50C (about 0.50mass%C), SK3 (about 1.0mass%C), and FC350 (about 3.0mass%C) were measured nondestructively by using a pulsed neutron transmission spectroscopy. The experiment was carried out at J-PARC/MLF BL10. The purpose of this work is to obtain a crystal structural information from the analysis of the Bragg edges (Fig. 1). The final goal of our study is to apply the results for the nondestructive research of iron cultural heritage such as Japanese sword and matchlock gun which were made of different carbon content steels .
Figure 1 shows the neutron transmission spectrum of S25C, S50C, SK3, and FC350. Each sample shows a distinctive shape of the Bragg edge, which provides information on texture. We obtained the lattice spacing d by analyzing the position of (110), (200), and (211) edges. As shown in Fig.2, steel samples less than 1.0mass%C have no significant difference on lattice constant. On the other hand, lattice constant of steel about 3.0mass%C decreases. This may be due to the formation of the graphite and/or the impurities in steel. It is concluded that lattice constant can be used as an indicator to identify forged iron and cast iron. We plan to use the results as basic data and to extend our study towards a systematic nondestructive measurement of iron cultural heritage.

TRUST LiCAFと波長シフトファイバーを用いた2次元中性子イメージングセンサーの開発

瓜谷章、山崎拓弥、渡辺賢一、山﨑淳、井口哲夫、福田健太郎、柳田健之　　　　　　　

平成27年度中性子イメージング専門研究会プログラム

開催年月日： 2016年1月

記述言語：日本語会議種別：口頭発表（一般）

開催地：京都大学原子炉実験所事務棟大会議室国名：日本国

平板状のTRUST LiCAF内部に、多数本の波長シフトファイバーをXY方向に配列させて作製した２次元中性子イメージングセンサーの諸特性について報告する。

Upgrade of Neutron Energy Spectrometer with Onion-like Single Bonner Sphere Using TRUST Eu:LiCAF Scintillator

T. Mizukoshi, K. Watanabe, A. Uritani, A. Yamazaki, T. Iguchi, T. Ogata, T. Muramatsu, T. Matsumoto, A. Masuda

開催年月日： 2015年12月

記述言語：英語会議種別：ポスター発表

国名：日本国

In order to measure neutron energy spectra, the conventional Bonner Sphere Spectrometers (BSS) are widely used. Operators should place these spheres in several times to a measurement point where radiation dose might be relatively high. In order to reduce this effort, novel neutron energy spectrometer using an onion-like single Bonner sphere was proposed in our group. This Bonner sphere has multiple sensitive spherical shell layers in the single sphere. In this spectrometer, a band-shaped thermal neutron detection medium, which consists of a LiF-ZnS mixed powder scintillator sheet and a wavelength-shifting (WLS) fiber readout, was looped to each sphere at equal angular intervals. Amount of LiF neutron converter is reduced near polar region in order to uniform the directional sensitivity. The LiF-ZnS mixed powder has an advantage of extremely high light yield. However, since it is opaque, this type of detector shows no characteristic shape in the pulse height spectrum. Subsequently, it is difficult to set the pulse height discrimination level. In order to solve this problem, we propose to replace the LiF-ZnS mixed powder into a flexible and Transparent RUbber SheeT type Eu:LiCaAlF6 (TRUST Eu:LiCAF) scintillator (Fig. 1). TRUST Eu:LiCAF scintillator can show a peak shape corresponding to neutron absorption events in the pulse height spectrum.
We fabricated the prototype detector with five sensitive layers using TRUST LiCAF scintillator and conducted basic experiments to evaluate the directional uniformity of the sensitivity. The fabricated detector shows excellent directional uniformity of the neutron sensitivity (Fig.2).

Development of position sensitive neutron detector using Transparent RUbber SheeT (TRUST) LiCaAlF₆ neutron scintillator with wavelength-shifting fiber

T. Yamazaki, K. Watanabe, A. Yamazaki, A. Uritani, T. Iguchi, T. Yanagida

開催年月日： 2015年12月

記述言語：英語会議種別：ポスター発表

国名：日本国

Development of alternatives to He-3 neutron detectors are required due to a He-3 shortage problem and increase in demand for neutron detectors in security and scientific applications. We have, therefore, developed a Transparent RUbber SheeT type Eu: LiCaAlF6 (TRUST LiCAF) neutron scintillator. This scintillator can easily be fabricated with a large area. For large area scintillators, wavelength-shifting(WLS) fiber readout is quite useful. The WLS fibers can also be inserted into a scintillator. The WLS fibers can absorb scintillation photons from the TRUST LiCAF and re-emit wavelength-shifted photons. In this paper, we demonstrate a neutron imaging using the TRUST LiCAF. We also evaluate the basic property.
Figure 1 shows schematic views of the neutron-detecting head. The also WLS fibers are arranged at a regular pitch of 2.0 mm in the x and y directions. The light photons re-emitted in the WLS fifbers propagate through itself to the 64-channel multianode PMTs that are connected at one side of each fiber. Figure 2 shows examples of neutron images acquired with the TRUST LiCAF scintillator and object made of a cadmium sheet. The incident position of a neutron is calculated by the center of gravity algorithm. The object was located in front of the neutron-detecting head. We successfully demonstrated that the TRUST LiCAF scintillator can acquire neutron images. As future works, we will evaluate the spatial resolution and other important properties.

Basic study on LET dependence of optical fiber type small size dosimeters using radiation-induced phosphor in 290 MeV/u carbon ions

Yuho HIRATA, Kenichi WATANABE, Akira URITANI, Atsushi YAMAZAKI, Yusuke KOBA, Naruhiro MATSUFUJI, Takayuki YANAGIDA, Kentaro FUKUDA

開催年月日： 2015年12月

記述言語：英語会議種別：ポスター発表

国名：日本国

Heavy ion therapy can form fine dose distribution and irradiate only a target organ. Although fine dose distribution can reduce undesired irradiation into normal organs, misalignment of an irradiation position may cause significant accidental exposure. In order to estimate the irradiation dose accurately, dosimeters are required to be inserted into an affected region in a patient body. We, therefore, have developed a small size dosimeter consisting of an optical fiber and a radiation-induced phosphor. This phosphor shows quenching effect when irradiated with high linear energy transition (LET) particles. In this paper, we discuss this LET dependence of luminescence dosimeters irradiated with 290 MeV/u carbon ions.
We fabricated the small size dosimeters with three phosphors, which were Eu:BaFBr, Ce:CaF2 and Bi4Ge3O12 (BGO). Carbon ions were irradiated into the fabricated dosimeters at Heavy Ion Medical Accelerator in Chiba (HIMAC). Fabricated dosimeters were set behind the water equivalent acrylic phantom. An ion chamber was also placed near the fabricated dosimeters as a reference.
Figure 1 shows the depth profiles of the luminescence signal intensities, which is observed by changing the phantom thickness. Fabricated dosimeters show a Bragg peak at the same position as the ion chamber. Luminescence efficiencies were decreased as a function of LET as shown in Figure 2. There is a difference in the reduction coefficient in the LET dependence of these phosphors luminescence efficiencies. We corrected the LET dependence of the luminescence efficiency with this difference. The corrected depth profile is shown in Figure 1.

Basic Study on Luminescence Property of Ho-doped Oxide Crystals

Yosuke Kumagai, Kenichi Watanabe , Akira Uritani , Atsushi Yamazaki, Takayuki Yanagida

開催年月日： 2015年12月

記述言語：英語会議種別：ポスター発表

国名：日本国

In radiation therapy which is one of remedy for cancer, it is important to enhance dose concentration to the diseased part. Particularly, we can form the extremely precise dose distribution in the ion beam radiotherapy, however, it is requested to improve the dose measurement technique for a guarantee on precise distribution. Therefore our group is advancing a development of small dosimeter that photostimulable phosphor is arranged on tip of an optical fiber. However photostimulable phosphors cause optically quenching in high LET radiation (heavy ion radiation). There are needed to be corrected LET effect for estimating accurate dose because these responses of the phosphor depend on not only dose but LET. We found the feasibility that correct LET effect by comparing responses of some phosphors which have each different response for LET effect. Therefore, various photostimulable phosphors are studied about LET effect evaluation. In this paper we discuss Ho-doped oxide crystal as new photostimulable and report its excitation and luminescence mechanism.

Study on Radiation Damage for TlBr Semiconductor Radiation Detectors

Motohiro Matsumura, Kenichi Watanabe, Atsushi Yamazaki, Akira Uritani, Nobumichi Nagano, Keitaro Hitomi

開催年月日： 2015年12月

記述言語：英語会議種別：ポスター発表

国名：日本国

Thallium bromide (TlBr) is one of attractive compound semiconductors for gamma-ray spectroscopy. The TlBr has the high stopping power which originates from its high atomic numbers (Tl=81, Br=35) and high density (7.56 g/cm3). The TlBr detector operates at room temperature because of the wide band-gap energy of 2.68 eV. The mobility-lifetime (μτ) products in TlBr crystals are respectively comparable to those for CdTe crystals.
Recently crystal-growth methods have been improved. Consequently it is reported that TlBr detector achieves resolution of < 1.0%. In order to show such a high performance, TlBr become one of the detectors which have high energy resolution and high detection efficiency at room-temperature for use in medicine and engineering. However, TlBr is still under development. The basic properties, such as the energy resolution and the peak to Compton ratio, have been examined. On the other hand, some important properties of TlBr in the practical stage are kept untouched. One of these problems is radiation hardness. If TlBr detectors have very low radiation hardness, it is deep problem for practical application. If TlBr detectors have high radiation hardness, TlBr stably operates in high dose rate field as one of the new application of TlBr detectors.
In this paper, we show a radiation hardness of TlBr semiconductor detectors for gamma-ray. We irradiated TlBr with gamma-ray emitted from 60Co (36.2 TBq). Total irradiation time is 24 hours. The radiation hardness has been observed using spectra and μτ products of electrons at interval of irradiation and after irradiation. The spectroscopic performance of TlBr detector for 137Cs was estimated at room temperature. Figure 1 shows that the ratios of peak channel are constant. Figure 2 shows that the spectrum shape isn't distorted after exposures. We confirm that the TlBr semiconductor detectors have strong resistance for gamma-ray.

多重球殻構造を有する単一減速材球型中性子スペクトロメータ

瓜谷章，水越友亮，渡辺賢一，山﨑淳，尾方智洋，村松貴史，増田明彦，松本哲郎

日本放射線安全管理学会　第14回学術大会

開催年月日： 2015年12月

記述言語：日本語会議種別：口頭発表（一般）

開催地：筑波大学国名：日本国

広エネルギー帯域の中性子スペクトロメータとして、ボナー球中性子スペクトロメータ（BSS）が広く用いられている。BSSは大きさが異なる複数の減速球を用いるため、測定時間が長くなること、また高線量場での測定では検出器交換の際の作業員の被ばく線量が問題となることがある。この問題を解決するために、筆者らは以前に一つのポリエチレン球内に複数の中性子検出器を球殻状に配置した一球型検出器1) を提案した。その一球型検出器では中性子検出器として不透明なLiF-ZnS(Ag) 混合体を使用しているため、信号波高分布が波高値に対し連続的に減少し、ピーク等の特徴的な形状を示さない。このため、波高弁別レベルを再現性をもって安定的に決定することが困難である。そこで本研究では透明であり、信号波高分布にピークを生じ、さらには柔軟で加工が容易な中性子検出媒体（TRUST LiCAF：Transparent RUbber SheeT type Eu:LiCaAlF6）を使用した検出器を試作し、応答関数の評価を行った。

ＬＨＤにおける総発生中性子計測と計測器校正

瓜谷章，仲野裕次，磯部光孝，小川国大，西谷建夫，渡辺賢一，山﨑淳

第32回プラズマ・核融合学会年会

Novel Digital Signal Processing Technique for TlBr Semiconductor Detector 国際会議

開催年月日： 2015年10月 - 2015年11月

記述言語：英語会議種別：ポスター発表

国名：日本国

The TlBr detector shows high gamma-ray detection efficiency because of its high atomic numbers and high density. However, the TlBr planer detector with more than 1mm thick can hardly operate with high energy resolution because the mobility-lifetime product (µt) of holes is not so high. In order for the sensitivity of the TlBr to be further improved, a thicker detector is required to be realized. In order to effectively read out the information of deposition energy in the TlBr detector, we study a novel digital signal processing technique. In conventional detectors, induced charges are accumulated for sufficient time to collect whole carrier information. However, in detectors with low carrier mobility, slow carriers, such as holes, may be captured before achieving to electrodes. One of the methods to eliminate information of slow carriers is a single polarity charge sensing technique, such as Frisch grid detector. For TlBr detector, capacitive Frisch grid technique was applied and excellent energy resolution was achieved. However, capacitive Frisch grid type detectors show asymmetric peak shape because of its imperfection in single polarity charge sensitivity. In this paper, we propose a novel digital signal processing technique extracting information of early carrier movement before carriers are captured. The increase rate of induced charges, or induced current, in a planner detector consisting of parallel plate electrodes is proportional to the total produced charge because carrier velocity and weighting potential are constant. The induced current in early period of a signal pulse is proportional to total produced charge or deposition energy. In order to confirm the feasibility of our proposed technique, we conducted basic experiments. We confirm that the induced current spectrum shows clearer and more symmetric peak shape than the conventional pulse height spectrum.

Characterization of Neutron Energy Spectrometer With Onion-like Single Bonner Sphere Using TRUST LiCAF Scintillator 国際会議

開催年月日： 2015年10月 - 2015年11月

記述言語：英語会議種別：ポスター発表

国名：日本国

Novel neutron energy spectrometer using an onion-like single Bonner sphere was proposed in our group. This Bonner sphere has multiple sensitive spherical shell layers in the single sphere and can obtain information for estimation of a neutron energy spectrum in one measurement. In this spectrometer, a band-shaped thermal neutron detection medium, which consists of a LiF-ZnS mixed powder scintillator sheet and a wavelength-shifting (WLS) fiber readout, was looped to each sphere at equal angular intervals. However, since the LiF-ZnS mixed powder scintillator shows no characteristic shape in the pulse height spectrum, it is difficult to set the pulse height discrimination level. In order to solve this problem, we replaced the LiF-ZnS mixed powder into a flexible and Transparent RUbber SheeT type LiCaAlF6 (TRUST LiCAF) scintillator. TRUST LiCAF scintillator can show a peak shape corresponding to neutron absorption events in the pulse height spectrum. To uniform the directional sensitivity, an amount of LiCAF neutron converter is reduced near polar region, where the detector media are concentrated. We fabricated the prototype detector with five sensitive layers using TRUST LiCAF scintillator. In this paper, we characterize the fabricated detector. We check the directional uniformity and the neutron energy dependence of the detector sensitivity. The detector shows excellent directional uniformity in the neutron sensitivity. We confirmed that the measured energy response, which was evaluated at monoenergetic neutron sources, agrees with the simulated one, which was calculated by Monte Carlo simulation code PHITS.

Correction of LET Dependence of an Optical Fiber Type Small OSL Dosimeter 国際会議

開催年月日： 2015年10月 - 2015年11月

記述言語：英語会議種別：ポスター発表

国名：日本国

Heavy ion therapy can form fine dose distribution and irradiate only a target organ. Although fine dose distribution can reduce undesired irradiation into normal organs, misalignment of an irradiation position may cause significant accidental exposure and/or deficiency of the irradiation dose into a tumor. In order to accurately estimate the irradiation dose, dosimeters are required to be inserted into an affected region in a patient body. We, therefore, have developed a small size dosimeter consisting of an optical fiber and an optically stimulated luminescence (OSL). This dosimeter can read out OSL signals through the optical fiber when irradiated with a stimulation laser. However, the OSL materials show quenching effect when irradiated with high linear energy transition (LET) particles. In this paper, we discuss the correction of LET dependence of small OSL dosimeters. We fabricated two types of small size dosimeters using different OSL materials, Eu:BaFBr and Ce:CaF2. Carbon ions were irradiated into the fabricated dosimeters at Heavy Ion Medical Accelerator in Chiba (HIMAC). The small size dosimeters were set behind the water equivalent acrylic phantom. We confirmed the luminescence efficiencies of Eu:BaFBr and Ce:CaF2 decrease with the LET. The ratio of the luminescence intensities between Eu:BaFBr and Ce:CaF2 also reduces as a function of the LET. We can obtain the LET value from this relation and then determine the luminescence efficiency of each dosimeter. We, therefore, can correct the LET dependence of the luminescence efficiency.

Development of One-Dimensional Wide X-Ray Line Sensor with a Parallel Plate Collimator for Backscattered X-Ray Inspection 国際会議

開催年月日： 2015年10月 - 2015年11月

記述言語：英語会議種別：ポスター発表

国名：日本国

Nondestructive internal inspections with imaging function are quite useful for large structures. Although a transmission X-ray imaging technique has high spatial resolution, it is unsuitable for large size structures because it is necessary to sandwich an object between an X-ray source and detectors. The backscattered X-ray imaging technique can be used for the internal visualization of large size structures because it can inspect from one-side of an object. Conventional backscattered X-ray inspection is conducted by two-dimensionally scanning a relatively low-energy pencil-beam X-ray, in which a rotating collimator is used for one-dimensional scanning. Higher energy X-ray is preferable to take an internal image of a large object because higher energy X-ray has higher penetration ability. However, pencil-beam scanning of high energy X-ray requires a heavy and large rotating collimator for beam shaping and scanning. We, therefore, proposed another approach, in which an X-ray beam is shaped into a fan-beam and a detector is one-dimensional position sensitive, for inspection of large size structures. Our detector has parallel plate collimator perpendicular to the plane of the fan-beam X-ray in order to define X-ray scattering positions. In this technique, we can obtain a one-dimensional backscattered X-ray profile in one measurement. We can conduct two-dimensional imaging by scanning only in one direction. The proposed system requires no heavy rotating collimator. In this paper, we fabricated the prototype detector and conducted basic experiments to confirm the feasibility of the proposed technique. We acquired the backscattered X-ray line profiles from a concrete slab object, when irradiating 950 keV linac X-rays. The acquired line profiles have intense signals corresponding to object positions. As future works, we will make a two dimensional image by scanning in the perpendicular direction to the fan-beam plane.

鉄文化財の材料特性と製造方法解明のためのパルス中性子透過法による鉄鋼材料研究

磯野真理子、田中眞奈子、塩田佳徳、渡辺賢一、鬼柳善明、瓜谷章

日本鉄鋼協会第170回秋季講演大会

臭化タリウム半導体検出器の耐放射線性

松村基広, 山崎淳, 渡辺賢一, 瓜谷章, 長野宣道, 人見啓太朗

第76回応用物理学会秋季講演会

後方散乱Ｘ線イメージングのためのマルチスリットコリメータ付一次元X線ラインセンサの開発

遠山貴之, 山﨑淳, 渡辺賢一, 瓜谷章, 豊川弘之, 藤原健, 萬代新一

第76回応用物理学会秋季講演会

パルス中性子ブラッグエッジ透過法と鉄鋼材料評価への応用

磯野真理子, 田中眞奈子, 塩田佳徳, 渡辺賢一, 鬼柳善明, 瓜谷章

第76回応用物理学会秋季講演会

Ho:YAP の光刺激蛍光に関する基礎研究

熊谷洋祐, 渡辺賢一, 山﨑淳, 瓜谷章, 柳田健之

第76回応用物理学会秋季講演会

インフラ診断用後方散乱X 線イメージング装置の開

豊川弘之,藤原健,萬代新一,伊佐英範,瓜谷章,渡辺賢一,山崎淳,遠山貴之,大橋和也,井上彬,夏井拓也,吉田光宏

第76回応用物理学会秋季講演会

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