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Journal Articles

Development of a new detector system to evaluate position and activity of plutonium particles in nasal cavities

Morishita, Yuki; Yamamoto, Seiichi*; Momose, Takumaro; Kaneko, Junichi*; Nemoto, Norio

Radiation Protection Dosimetry, 178(4), p.414 - 421, 2018/03

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

Plutonium dioxide (PuO$$_{2}$$) is used to fabricate a mixed oxide fuel for fast breeder reactors. When a glove box containing PuO$$_{2}$$ fails, such as by rupture of a glove or a vinyl bag, airborne contamination of plutonium (Pu) can occur. If the worker inhale PuO$$_{2}$$ particles, they deposit in the lung and cause lung cancer. The nasal smear and nose blow methods are useful for checking workers for PuO$$_{2}$$ intake in the field. However, neither method can evaluate the quantitative activity of Pu. No alpha-particle detector that can be used for direct measurements in the nasal cavity has been developed. Therefore, we developed a nasal monitor capable of directly measuring the activity of Pu in the nasal cavity to precisely evaluate the internal exposure dose of a worker. Prismatic-shaped 2$$times$$2 acrylic light guides were used to compose a detector block, and a ZnS(Ag) scintillator was adhered to the surface of these light guides. Silicon photomultiplier (SiPM) arrays with 8$$times$$8 channels were used as a photodetector. Actual PuO$$_{2}$$ particles were measured using the nasal monitor. The nasal monitor could be directly inserted in the nasal cavities. The activity distribution of Pu was obtained by the nasal monitor. The average efficiencies in 4$$pi$$ were 11.43% and 11.58% for the left and right nasal cavities, respectively. The effect of $$gamma$$ and $$beta$$ rays on the detection of the alpha particles of Pu was negligible. The difference in the measured Pu activity between the ZnS(Ag) scintillation counter and the nasal monitor was within 4.0%. The developed nasal monitor can solve the uncertainty problem encountered with the nasal smear and the nose blow methods. We expect this monitor to be useful for accurately estimating the internal exposure dose of workers.

Journal Articles

Flexible alpha camera for detecting plutonium contamination

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Nemoto, Norio

Radiation Measurements, 103, p.33 - 38, 2017/08

 Times Cited Count:13 Percentile:82.55(Nuclear Science & Technology)

Nuclear fuel materials, such as uranium and plutonium (Pu), are handled at nuclear fuel facilities. There are a contamination source of Pu in tight spaces that cannot be directly measured by a ZnS(Ag) scintillation detector, such as interspace between a glovebox window and a platform, pipe flange, port cover of vinyl bag, and filter interspaces. Therefore, we developed a new imaging detector called a flexible alpha camera that enables to identify the Pu contamination for tight spaces at work sites. The thickness of the flexible alpha camera was only $$sim$$1/5 of the ZnS(Ag) scintillation detector, and its efficiency for 4-pi direction was 42.7% for 5.5-MeV alpha particles. Minimal detectable activity (MDA) was 0.014 Bq. Four types of PuO$$_{2}$$ sample, removed from a duct, Bag-In/Bag-Out port, glovebox glove, and vinyl sheet, were measured by the flexible alpha camera and the PuO$$_{2}$$ particle was automatically identified. Using the flexible alpha camera, the Pu contamination source can be quickly detected, preventing the spread of contamination.

Journal Articles

Positron annihilation lifetime of irradiated polyimide

Hirade, Tetsuya; Oka, Toshitaka; Morishita, Norio*; Idesaki, Akira; Shimada, Akihiko

Materials Science Forum, 733, p.151 - 154, 2013/00

 Times Cited Count:7 Percentile:94.44

Polyimide polymers such as Kapton show a very good performance at high radiation environment such as in space or in radiation facilities. Positron annihilation lifetime measurement is a widely used method for materials science, and the lifetime of triplet positronium (electron-positron pair) can give important information of free volume of polymers. However, there is no positronium formation in Kapton and hence this method was no applied for polymer studies. Here, we indicated that free positron annihilation lifetime can give information of change of free volume by showing the temperature dependence of the lifetime. We applied this method to study irradiation effects on Kapton and we successfully indicated that the free positron lifetime can be applied for polymer studies.

Journal Articles

Capacitance transient study of a bistable deep level in e$$^{-}$$-Irradiated n-type 4H-SiC

Beyer, F. C.*; Hemmingsson, C. G.*; Pedersen, H.*; Henry, A.*; Isoya, Junichi*; Morishita, Norio*; Oshima, Takeshi; Janz$'e$n, E.*

Journal of Physics D; Applied Physics, 45(45), p.455301_1 - 455301_7, 2012/11

 Times Cited Count:14 Percentile:53.06(Physics, Applied)

Journal Articles

Electrically Detected Magnetic Resonance (EDMR) studies of SiC-SiO$$_{2}$$ interfaces

Umeda, Takahide*; Kosugi, Ryoji*; Fukuda, Kenji*; Morishita, Norio*; Oshima, Takeshi; Ezaki, Kana*; Isoya, Junichi*

Materials Science Forum, 717-720, p.427 - 432, 2012/05

 Times Cited Count:6 Percentile:94.47

Metal-Oxide (SiO$$_{2}$$)-Semiconductor (MOS) structures fabricated on Silicon Carbide (SiC) were studied using Electrically Detected Magnetic Resonance technique (EDMR). The residual Carbons are expected to be near the interface between SiC and SiC-SiO$$_{2}$$SiO$$_{2}$$, which is different from Si-SiO$$_{2}$$ interface. By the EDMR measurements at 50K, a defect center related to C dangling bonds which is called P$$_{H1}$$ center and also a center related to C dangling bonds terminated by hydrogens or nitrogens (Ns) which is called P$$_{H1}$$ were observed. In addition, a center related to N donor which is called Nh exist near the interface from N-treatment samples. This suggests that carrier concentration increases near the interface due to the introduction of donors, and as a result, the channel conductance increases.

Journal Articles

Behavior of nitrogen atoms in SiC-SiO$$_{2}$$ interfaces studied by electrically detected magnetic resonance

Umeda, Takahide*; Ezaki, Kana*; Kosugi, Ryoji*; Fukuda, Kenji*; Oshima, Takeshi; Morishita, Norio*; Isoya, Junichi*

Applied Physics Letters, 99(14), p.142105_1 - 142105_3, 2011/10

 Times Cited Count:46 Percentile:85.39(Physics, Applied)

Journal Articles

Annealing behavior of the EB-centers and M-center in low-energy electron irradiated $$n$$-type 4H-SiC

Beyer, F. C.*; Hemmingsson, C.*; Pedersen, H.*; Henry, A.*; Janz$'e$n, E.*; Isoya, Junichi*; Morishita, Norio*; Oshima, Takeshi

Journal of Applied Physics, 109(10), p.103703_1 - 103703_6, 2011/05

 Times Cited Count:16 Percentile:57.21(Physics, Applied)

By low-energy electron (200 keV) irradiation into epitaxial n-type 4H-SiC with a dose of 5$$times$$10$$^{16}$$/cm$$^{2}$$, the bistable M-center is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is investigated. During the annihilation process of M-center, the bistable EB-centers are detected in the low temperature range of the DLTS spectrum. The value of annealing energy of the M-center is similar to the generation energy of the EB-centers. This suggests that the M-center partially transforms to the EB-centers by annealing. The EB-centers completely disappeared after annealing temperatures higher than 700 $$^{circ}$$C. Since the threshold energy for moving Si atom in SiC is higher than the applied irradiation energy of electrons, and the annihilation temperatures are relatively low, the M-center and the EB-centers are attributed to defects related to the C atom in SiC.

Journal Articles

ESR study on radiation-induced radicals in carboxymethyl cellulose aqueous solution

Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Kudo, Hisaaki*; Katsumura, Yosuke*

Radiation Physics and Chemistry, 80(2), p.149 - 152, 2011/02

 Times Cited Count:14 Percentile:71.49(Chemistry, Physical)

Carboxymethyl cellulose (CMC), one of polysaccharide derivatives, at highly concentrated aqueous solution undergoes radiation-crosslinking reactions. In this topic, CMC radical, formed by reaction with OH radical attributed to radiation-induced crosslinking reaction, were studied by ESR method to understand the radiation-induced reaction mechanism of CMC aqueous solution. At first, it was succeeded to observe ESR spectra of the CMC radical using photolysis of hydrogen peroxide as the origin of OH radical. Observed ESR spectra were identified as radicals located on the secondary carbon of carboxymethyl groups. Secondly, N$$_{2}$$O saturated CMC aqueous solution 6 min after electron beam irradiation was measured by ESR method. The spectra were almost same shape as the case of photolysis of hydrogen peroxide, and were assigned as long-lived radicals located on carboxymethyl groups. Next, in the case of N$$_{2}$$ and O$$_{2}$$ saturation, spectra intensity become half or 0. This means that these long-lived radicals are produced by reaction with OH radical.

Journal Articles

Radiation-induced graft polymerization of functional monomer into poly(ether ether ketone) film and structure-property analysis of the grafted membrane

Hasegawa, Shin; Takahashi, Shuichi*; Iwase, Hiroki*; Koizumi, Satoshi; Morishita, Norio; Sato, Ken*; Narita, Tadashi*; Onuma, Masato*; Maekawa, Yasunari

Polymer, 52(1), p.98 - 106, 2011/01

 Times Cited Count:45 Percentile:81.93(Polymer Science)

Radiation-induced graft polymerization of sulfo-containing styrene derivatives into poly(ether ether ketone) (PEEK) substrates was carried out to prepare thermally and mechanically stable polymer electrolyte membranes based on an aromatic hydrocarbon polymer. Graft polymerization of ethyl 4-styrenesulfonate into a 32% crystallinity degree PEEK substrate hardly progressed, whereas graft polymerization into 11% PEEK substrate gradually progressed, achieving a grafting degree of more than 50% after 72 h. From Electron Spin Resonance analysis of irradiated PEEK films, it apparent the graft polymerization initiate from the phenoxy radicals. Small-angle X-ray scattering and small-angle neutron scattering observations clearly showed that the graft-type PEEK membranes possessed ion channel domains with the average distance of 13 nm, being larger than that of Nafion. Furthermore, there was a micro-structure in the ion channels with the average distance of 1.8 nm.

Journal Articles

EPR and ${it ab initio}$ calculation study on the EI4 center in 4$$H$$- and 6$$H$$-SiC

Carlsson, P.*; Son, N. T.*; Gali, A.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Magnusson, B.*; Janz$'e$n, E.*

Physical Review B, 82(23), p.235203_1 - 235203_11, 2010/12

 Times Cited Count:10 Percentile:44.56(Materials Science, Multidisciplinary)

Electron Paramagnetic Resonance (EPR) studies of the EI4 center in 4$$H$$- and 6$$H$$-Silicon Carbide (SiC) were carried out. The EI4 center was drastically enhanced in electron-irradiated high-purity semi-insulating materials by annealing at 700-750 $$^{circ}$$C. An additional large-splitting $$^{29}$$Si hf structure and $$^{13}$$C hf lines of the EI4 defect were observed. Comparing the data obtained from the hf interactions and the annealing behavior, and also from ${it ab initio}$ supercell calculations of different carbon-vacancy-related complexes, we propose a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third-neighbor site of the antisite in the neutral charge state, (V$$_{C}$$-C$$_{Si}$$V$$_{C}$$)$$^{0}$$, as a new defect model for the EI4 center.

Journal Articles

Fluorine-vacancy defects in fluorine-implanted silicon studied by electron paramagnetic resonance

Umeda, Takahide*; Isoya, Junichi*; Oshima, Takeshi; Onoda, Shinobu; Morishita, Norio; Okonogi, Kensuke*; Shiratake, Shigeru*

Applied Physics Letters, 97(4), p.041911_1 - 041911_3, 2010/07

 Times Cited Count:5 Percentile:24.28(Physics, Applied)

Journal Articles

Spin conversion of positronium in NiO/Al$$_{2}$$O$$_{3}$$ catalysts observed by coincidence Doppler broadening technique

Zhang, H. J.*; Chen, Z. Q.*; Wang, S. J.*; Kawasuso, Atsuo; Morishita, Norio

Physical Review B, 82(3), p.035439_1 - 035439_8, 2010/07

 Times Cited Count:25 Percentile:70.46(Materials Science, Multidisciplinary)

Positronannihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/Al$$_{2}$$O$$_{3}$$ catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetime components correspond to ortho-positronium (o-Ps) annihilated in microvoids and large pores, respectively. With increasing NiO content, both the latter lifetime and intensity show continuous decrease. Meanwhile, the para-positronium (p-Ps) intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of Ps in NiO/Al$$_{2}$$O$$_{3}$$ catalysts. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.

Journal Articles

ESR study on carboxymethyl chitosan radicals in an aqueous solution

Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Muroya, Yusa*; Kudo, Hisaaki*; Katsumura, Yosuke*

Radiation Physics and Chemistry, 79(3), p.276 - 278, 2010/03

 Times Cited Count:11 Percentile:61.1(Chemistry, Physical)

Carboxymethyl chitosan (CMCTS) is one kind of polysaccharide derivatives and has a good water-solubility. At a high concentrated aqueous solution, CMCTS forms gel by ionizing irradiation, though polysaccharide derivatives are generally radiation-degradation type. In general, OH radical, which is one of main water radiolysis products and very oxidative species, is said to induce crosslinking reaction of polymer solution. The purpose of this study is to understand the radiation-crosslinking mechanism of CMCTS at a high concentrated aqueous solution. In this study, identification of CMCTS radical produced by reaction with OH radical was introduced. CMCTS radical in an aqueous solution was observed directly by ESR method using photolysis of hydrogen peroxide. The ESR spectra have a large doublet split and small triplet split like [Triplet $$times$$ Doublet]. However, some species seemed to be overlapped on ESR spectra, because right-and-left triplet spectra are not equiform. Compared with some radicals, which have analogical structure to CMCTS, about hyperfine coupling constant, [Triplet $$times$$ Doublet], assigned as radical on carboxymethyl group linked to C6, and [Doublet], assigned as radical on carboxymethyl group linked to C2 or C3, were isolated from ESR spectra of experimental results. In conclusion, these spectra were identified as radicals located on secondary carbon of carboxymethyl groups.

Journal Articles

ESR study of free radicals in mango

Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Ukai, Mitsuko*; Kobayashi, Yasuhiko; Shimoyama, Yuhei*

Spectrochimica Acta, Part A, 75(1), p.310 - 313, 2010/01

An electron spin resonance (ESR) spectroscopic study of radicals induced in irradiated fresh mangoes was performed. Mangoes in the fresh state were irradiated with $$gamma$$-rays, lyophilized and then crushed into a powder. The ESR spectrum of the powder showed a strong main peak at ${it g}$ = 2.004 and a pair of peaks centered at the main peak. The main peak was detected from both flesh and skin specimens. This peak height gradually decreased during storage following irradiation. On the other hand, the side peaks showed a well-defined dose-response relationship even at 9 days post-irradiation. The side peaks therefore provide a useful means to define the irradiation of fresh mangoes.

Journal Articles

The Carbon vacancy related EI4 defect in 4H SiC

Son, N. T.*; Carlsson, P.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Magnusson, B.*; Janz$'e$n, E.*

Materials Science Forum, 645-648, p.399 - 402, 2010/00

Defects in high-purity semi-insulating 4H SiC irradiated with 2 MeV electrons at room temperature were studied using Electron paramagnetic resonance (EPR). The EPR signal named EI4 defect increased with annealing temperature up to 750 $$^{circ}$$C. Additional large-splitting $$^{29}$$Si hyperfine (hf) structures and $$^{13}$$C hf lines by the interaction with one $$^{13}$$C nucleus were investigated. Based on the observed hf structures, the C$$_{1h}$$ symmetry as well as the annealing behaviour, the EI4 defects is determined to be the complex between two carbon vacancies and a carbon antisite in the neutral charge state, V$$_{C}$$V$$_{C}$$C$$_{Si}$$$$^{0}$$. The formation of the complex is interpreted in terms of the migration of the silicon vacancy and the formation of the carbon vacancy-carbon antisite pair next to a carbon vacancy.

Journal Articles

Metastable defects in low-energy electron irradiated n-type 4H-SiC

Beyer, F. C.*; Hemmingsson, C.*; Pedersen, H.*; Henry, A.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Janz$'e$n, E.*

Materials Science Forum, 645-648, p.435 - 438, 2010/00

By low-energy electron irradiation of epitaxial n-type 4H-SiC, the Deep Level Transient Spectroscopy (DLTS) peaks called the defects Z1/2 and EH6/7 were observed, which were also observed in as-grown layer and the commonly found peaks EH1 and EH3 (M-center) also appeared. New defect named the EB-centers increased after annealing out of EH1 and EH3. Since low energy electron irradiation (less than 220 keV) affects mainly the carbon atom in SiC, both the M- and EB-centers might be carbon related defects.

Journal Articles

ESR method for detecting irradiated fresh mangoes

Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Sakashita, Tetsuya; Funayama, Tomoo; Ukai, Mitsuko*; Shimoyama, Yuhei*; Kobayashi, Yasuhiko

JAEA-Review 2009-041, JAEA Takasaki Annual Report 2008, P. 86, 2009/12

When tropical fruits are imported, quarantine treatments are required for preventing plant pests. The irradiation is a choice of the quarantine treatments for tropical fruits in the world. When the irradiation is utilized as the treatment, detection methods are required to endorse the reliability of labels for consumers. To distinguish the irradiated fresh mangoes from non-irradiated ones, radical detection was carried out using ESR. After freeze-drying mangoes, the ESR main peak was observed but the signal intensity was affected by ripeness and period of storage. We found that the existence of side peaks is an effective indicator to detect fresh mangoes irradiated to dose range of quarantine treatment. Since ESR method is able to measure without complicate preparation, this technique is useful to detect the irradiation treatment against a wide variety of foods.

Journal Articles

Radiation-induced graft polymerization of styrene into a poly(ether ether ketone) film for preparation of polymer electrolyte membranes

Hasegawa, Shin; Sato, Ken*; Narita, Tadashi*; Suzuki, Yasuyuki; Takahashi, Shuichi; Morishita, Norio; Maekawa, Yasunari

Journal of Membrane Science, 345(1-2), p.74 - 80, 2009/12

 Times Cited Count:31 Percentile:70.64(Engineering, Chemical)

Radiation-induced graft polymerization of styrene into poly(ether ether ketone) (PEEK) with 32% crystallinity was investigated with DSC, TGA, XRD, and ESR. Endothermic heats of melting of the original and styrene-grafted PEEK (grafted PEEK) films were similar, indicating the crystallinity was almost completely maintained up to a grafting degree of 51%. Lower glass transition temperature of the grafted PEEK film in the DSC, and the absence of an extra halo originating from amorphous polystyrene grafts in the XRD strongly indicate the grafting of styrene to crystalline PEEK films proceeded in the amorphous region of PEEK. This is probably because polystyrene grafts have hydrocarbon structures similar to a base PEEK polymer, resulting in compatibility to the amorphous phase of the PEEK films. The grafted PEEK films can be converted to PEEK-based electrolyte membranes by subsequent sulfonation, and had conductivity of more than 0.01 S/cm and exhibited higher water content above 100%.

Journal Articles

An ESR study of radicals induced in irradiated fresh mango

Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Ukai, Mitsuko*; Shimoyama, Yuhei*; Kobayashi, Yasuhiko

Radioisotopes, 58(12), p.789 - 797, 2009/12

no abstracts in English

Journal Articles

Identification of the gallium vacancy-oxygen pair defect in GaN

Son, N. T.*; Hemmingsson, C. G.*; Paskova, T.*; Evans, K. R.*; Usui, Akira*; Morishita, Norio; Oshima, Takeshi; Isoya, Junichi*; Monemar, B.*; Janz$'e$n, E.*

Physical Review B, 80(15), p.153202_1 - 153202_4, 2009/10

 Times Cited Count:38 Percentile:79.73(Materials Science, Multidisciplinary)

GaN samples were irradiated with electrons of 2 MeV at 1$$times$$10$$^{19}$$/cm$$^{2}$$, and electron spin resonance (ESR) was measured at 77 K. As a result, four defect signals which are labeled D1 to D4 were observed. The D2 signal was identified to be negatively charged gallium vacancy - oxygen pair from the details studies of $$^{14}$$N hf structure.

131 (Records 1-20 displayed on this page)