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Tamura, Koji; Oba, Hironori; Saeki, Morihisa; Taguchi, Tomitsugu*; Lim, H. H.*; Taira, Takunori*; Wakaida, Ikuo
Journal of Nuclear Science and Technology, 58(4), p.405 - 415, 2021/04
Times Cited Count：1 Percentile：39.17(Nuclear Science & Technology)Radiation dose rate effects on the properties of a compact fiber-optic laser-induced breakdown spectroscopy (LIBS) system with a monolithic Nd:YAG/Cr:YAG composite ceramics were investigated for remote analysis in hazardous environment. To investigate radiation effects on the LIBS signal, properties related to the Nd:YAG laser operation such as oscillation threshold, output energy, oscillation timing, temporal pulse shape, and beam profile were measured as a function of the radiation dose rate from 0 to 10 kGy/hr in view of their influences to the signal. LIBS spectra of zirconium metal were measured under irradiation. Although signal intensity decreased considerably by irradiation, informative spectra were well obtained even at the maximum radiation dose rate. From the comparison of the LIBS-related parameters among the laser properties, signal reduction was mainly ascribed to the pulse energy reduction. Scintillation emission spectra were also measured from the ceramics during the irradiation, where the signal intensity increased linearly with the dose rate. The results show that the developed system.
Nakanishi, Ryuzo; Oba, Hironori; Saeki, Morihisa; Wakaida, Ikuo; Tanabe, Rie*; Ito, Yoshiro*
Optics Express (Internet), 29(4), p.5205 - 5212, 2021/02
Times Cited Count：0 Percentile：0(Optics)Laser-induced breakdown spectroscopy (LIBS) combined with liquid jets was applied to the detection of trace sodium (Na) in aqueous solutions. The sensitivities of two types of liquid jets were compared: a liquid cylindrical jet with a diameter of 500 
m and a liquid sheet jet with a thickness of 20 m. Compared with the cylindrical jet, the liquid sheet jet effectively reduced the splash from the laser-irradiated surface and produced long-lived luminous plasma. The limit of detection (LOD) of Na was determined to be 0.57 g/L for the sheet jet and 10.5 g/L for the cylindrical jet. The LOD obtained for the sheet jet was comparable to those obtained for commercially available inductively coupled plasma emission spectrometers.
Saeki, Morihisa*; Yomogida, Takumi; Matsumura, Daiju; Saito, Takumi*; Nakanishi, Ryuzo*; Tsuji, Takuya; Oba, Hironori*
Analytical Sciences, 36(11), p.1371 - 1378, 2020/11
Times Cited Count：0 Percentile：0(Chemistry, Analytical)We measured X-ray absorption fine structure (XAFS) and Raman spectra of isopolymolybdates(VI) in HNO
solution (0.15- 4.0 M), which change their geometries depending on acid concentration, and performed simultaneous resolution of the XAFS and Raman data using a multivariate curve resolution by alternating least-squares (MCR-ALS) analysis. In iterative ALS optimization, initial data matrices were prepared by two different methods. The MCR-ALS result of single XAFS data matrix shows large dependence on the preparation method of the initial data matrices. The MCR-ALS result of an augmented matrix of Raman and XAFS data has little dependence on the initial data matrices. It indicates that the augmentation method effectively improves the rotation ambiguities in the MCR-ALS analysis of the XAFS data. Based on the model fitting of the pure EXAFS oscillations, we revealed the change of [Mo
O
(H
O)
]
[MoO
(HO)
] [HMoO(HO)]
in the highly concentrated HNO solution.
Pd in Pd purified by selective precipitation from spent nuclear fuel by laser ablation ICP-MSAsai, Shiho; Ohata, Masaki*; Yomogida, Takumi; Saeki, Morihisa*; Oba, Hironori*; Hanzawa, Yukiko; Horita, Takuma; Kitatsuji, Yoshihiro
Analytical and Bioanalytical Chemistry, 411(5), p.973 - 983, 2019/02
Times Cited Count：5 Percentile：57.47(Biochemical Research Methods)Determination of radiopalladium Pd is required for ensuring the radiation safety of Pd extracted from spent nuclear fuel for recycling or disposal. We employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to simplify an analytical procedure of Pd. Pd was separated through selective Pd precipitation reaction from spent nuclear fuel. Laser ablation allows direct measurement of the Pd precipitates, skipping the dissolution and dilution procedure. In this study, 
Pd in natural Pd standard solution was used as an internal standard, taking advantage of its absence in spent nuclear fuel. The Pd precipitate was uniformly embedded on the surface of the centrifugal filter, forming a microscopically thin flat surface of Pd. The resulting homogeneous Pd layer is suitable for obtaining a stable signal ratio of Pd/Pd. The amount of Pd obtained by LA-ICP-MS corresponds to the values obtained by conventional solution nebulization measurement.
Saeki, Morihisa*; Matsumura, Daiju; Yomogida, Takumi; Taguchi, Tomitsugu*; Tsuji, Takuya; Saito, Hiroyuki*; Oba, Hironori*
Journal of Physical Chemistry C, 123(1), p.817 - 824, 2019/01
Times Cited Count：6 Percentile：37.24(Chemistry, Physical)Reaction kinetics of laser-induced particle formation in an aqueous solution of PdCl
was investigated by transmission electron microscope (TEM) and dispersive X-ray absorption fine structure (DXAFS). The Pd particle was generated by irradiation of nanosecond pulsed 266-nm laser. The TEM observation showed dependence of the particle size on the laser fluence and promotion of the particle growth by irradiation of high-fluence laser. The DXAFS data give us the Pd concentration. Temporal changes of the Pd concentration analyzed based on Finke-Watzky two step mechanism. The analysis elucidates that the laser photon contributes to the reduction of the PdCl ion by the one-photon process and to the autocatalytic growth of the Pd particles by the multi-photon process.
Wakaida, Ikuo; Oba, Hironori; Miyabe, Masabumi; Akaoka, Katsuaki; Oba, Masaki; Tamura, Koji; Saeki, Morihisa
Kogaku, 48(1), p.13 - 20, 2019/01
By Laser Induced Breakdown Spectroscopy and by related resonance spectroscopy, elemental and isotope analysis of Uranium and Plutonium for nuclear fuel materials and in-situ remote analysis under strong radiation condition for melt downed nuclear fuel debris at damaged core in "Fukushima Daiichi Nuclear Power Station", are introduced and performed as one of the application in atomic energy research field.
Saeki, Morihisa*; Asai, Shiho; Oba, Hironori*
Bunseki, 2018(4), p.138 - 143, 2018/04
Platinum group metal (PGM) has attracted much attention in light of increasing demands in the industrial sector. A wide variety of techniques specialized for PGM separation, such as, solvent extraction, solid phase extraction, and molten salt electrolysis have been developed so far. Among such techniques, a newly developed separation technique based on laser-induced particulate formation can be a promising alternative to conventional ones. It enables non-contact and highly-selective separation with a simple operation. In this review, the research history and the basic mechanism of laser-induced particulate formation were outlined. Several applications were also mentioned, focusing on our latest research progress which achieved a world first quantitation of radioactive palladium in a spent nuclear fuel sample.
Pd by ICP-MS; The Relation between separation conditions and Pd recoveryYomogida, Takumi; Asai, Shiho; Saeki, Morihisa*; Hanzawa, Yukiko; Horita, Takuma; Esaka, Fumitaka; Oba, Hironori*; Kitatsuji, Yoshihiro
Bunseki Kagaku, 66(9), p.647 - 652, 2017/09
Times Cited Count：1 Percentile：5.18(Chemistry, Analytical)Palladium-107 is a long-lived fission product, which can be found in high-level radioactive liquid wastes (HLLW). Determination of the Pd contents in HLLW is essential to evaluate the long-term safety of HLLW repositories. However, the Pd content in HLLW has not been reported because of difficulties in pretreatment for the measurement. In this study, we investigated applicability of laser-induced photoreduction to HLLW solution: it enables a simple and non-contact separation of Pd. The results showed the recovery of 60% was achieved at the conditions: 40% ethanol, 20 min irradiation, 100 mJ of pulse energy. Additionally, major radionuclides and potentially interfering components in ICP-MS were removed from the simulated HLLW over a wide concentration range of Pd from 0.24 to 24 mg L
, showing the applicability of the proposed separation technique to HLLW samples.
Saeki, Morihisa*; Taguchi, Tomitsugu*; Oba, Hironori*; Matsumura, Daiju; Tsuji, Takuya; Yomogida, Takumi
Denki Gakkai Kenkyukai Shiryo, Denshi Zairyo Kenkyukai (EFM-17-010
021), p.15 - 18, 2017/09
Irradiation of nanosecond pulsed UV laser into a solution of palladium ion leads to formation of palladium particles with sub-micron size particles by time-resolved X-ray absorption spectroscopy.
Pd in Pd recovered by laser-induced photoreduction with inductively coupled plasma mass spectrometryAsai, Shiho; Yomogida, Takumi; Saeki, Morihisa*; Oba, Hironori*; Hanzawa, Yukiko; Horita, Takuma; Kitatsuji, Yoshihiro
Analytical Chemistry, 88(24), p.12227 - 12233, 2016/12
Times Cited Count：10 Percentile：47.49(Chemistry, Analytical)Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, Pd, which can be found in radioactive wastes, is one of the difficult-to-measure nuclides and results in a deficit in experimentally determined contents. In this study, a precipitation-based separation method has been developed for the determination of Pd with ICP-MS. The photoreduction induced by laser irradiation at 355 nm provides short-time and one-step recovery of Pd. The proposed method was verified by applying it to a spent nuclear fuel sample. In order to efficiently recover Pd, a natural Pd standard was employed as the Pd carrier. The chemical yield of Pd was about 90% with virtually no impurities, allowing accurate quantification of Pd.
Saeki, Morihisa; Taguchi, Tomitsugu; Nakashima, Nobuaki*; Oba, Hironori
Journal of Photochemistry and Photobiology A; Chemistry, 299, p.189 - 193, 2015/02
Times Cited Count：7 Percentile：21.94(Chemistry, Physical)Oba, Hironori; Saeki, Morihisa; Wakaida, Ikuo
Reza Kenkyu, 42(12), p.892 - 896, 2014/12
Laser-induced breakdown spectroscopy (LIBS) is an attractive technique for determining elemental composition in real time, in-situ and remotely without any sample preparation. The LIBS analysis of metal ions in an aqueous solution is available in process control and environmental monitoring. In the present paper, we have reviewed the LIBS methods for a liquid phase that tried to improve the detection sensitivity. We have performed the LIBS measurement with the sheet flow for the simultaneous determination of elements in the simulated high-level radioactive waste liquid and have discussed on the application possibility as a tool for online process monitoring.
Oba, Hironori; Saeki, Morihisa; Wakaida, Ikuo; Tanabe, Rie*; Ito, Yoshiro*
Optics Express (Internet), 22(20), p.24478 - 24490, 2014/10
Times Cited Count：14 Percentile：66.41(Optics)For aqueous-solution-based elemental analysis, we used a thin liquid sheet (m-scale thickness) in laser-induced breakdown spectroscopy with nanosecond laser pulses. Laser-induced plasma is emitted by focusing a pulsed Nd:YAG laser (1064 nm) on a 5- to 80-m-thick liquid sheet in air. To optimize the conditions for detecting elements, we studied how the signal-to-background ratio (SBR) for H
Balmer and Na-neutral emission lines depends on the liquid-sheet thickness. The SBR of the H Balmer and Na-neutral lines was maximized for a sheet thickness of 20 m at the laser energy of 100 mJ. The hydrodynamics of liquid flow induced by the laser pulse was analyzed by laser flash shadowgraph imaging. Time-resolved observation of the hydrodynamics and plasma emission suggests that the dependence of the SBR on the liquid-sheet thickness is correlated with the volume of flowing liquid that interacts with the laser pulses.
Saeki, Morihisa; Iwanade, Akio; Ito, Chikara; Wakaida, Ikuo; Thornton, B.*; Sakka, Tetsuo*; Oba, Hironori
Journal of Nuclear Science and Technology, 51(7-8), p.930 - 938, 2014/07
Times Cited Count：49 Percentile：98.47(Nuclear Science & Technology)To inspect post-accident nuclear core reactor of the TEPCO Fukushima Daiichi Nuclear Power Plant, a transportable fiber-coupled LIBS instrument was developed. The developed LIBS instrument was designed to analyze the underwater sample in high-radiation field by single-pulse breakdown with gas flow or double-pulse breakdown. To check the feasibility of the assembled fiber-coupled LIBS instrument to the inspection inside Fukushima Daiichi Nuclear Power Plant, we investigated (1) influence of radiation dose on optical transmittance of the laser delivery fiber, (2) survey of the LIBS techniques to analyze the underwater sample and (3) candidates of emission lines for analysis of the debris. By employing the selected emission lines, we demonstrated that the developed LIBS instrument can analyze the simulated debris underwater by the single-pulse breakdown with the gas flow with high signal to noise ratio.
Ito, Chikara; Naito, Hiroyuki; Nishimura, Akihiko; Oba, Hironori; Wakaida, Ikuo; Sugiyama, Akira; Chiyatani, Keiji
Journal of Nuclear Science and Technology, 51(7-8), p.944 - 950, 2014/07
Times Cited Count：12 Percentile：75.09(Nuclear Science & Technology)In the Fukushima Daiichi Nuclear Power Station, it is necessary to survey the locations and conditions of fuel debris inside reactor pressure vessels or primary containment vessels under water and radiation environment in preparation for removing fuel debris. An optical fiber is well known for features such as signal transmission, light weight, superior insulation performance, water resistance and electromagnetic noise resistance. These features allow the optical fiber to simplify the instrumentation systems for in-vessel inspection, as long as provide that the optical fiber can be used under high radiation dose environment. The radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000 ppm in pure silica fiber. The improved optical fibers were irradiated with 
-ray up to 1 
10
Gy using a 
Co source. They indicated a large peak around 600 nm and a peak tail from ultraviolet region, but no large absorption in infrared region except a hydroxyl absorption peak of 945 nm. We have confirmed that the optical fiber containing 1000 ppm hydroxyl has enough radiation resistance for radiation induced transmission losses and the infrared imaging is effective for observation under high radiation doses.
Ito, Chikara; Naito, Hiroyuki; Oba, Hironori; Saeki, Morihisa; Ito, Keisuke; Ishikawa, Takashi; Nishimura, Akihiko; Wakaida, Ikuo; Sekine, Takashi
Proceedings of 22nd International Conference on Nuclear Engineering (ICONE-22) (DVD-ROM), 7 Pages, 2014/07
A high-radiation resistant optical fiber has been developed in order to investigate the interiors of the reactor pressure vessels and the primary containment vessels of the Fukushima Daiichi Nuclear Power Station. The radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000 ppm in pure silica fiber. The improved image fiber consists of common cladding and a large number of fiber cores made from pure silica that contains 1000 ppm hydroxyl. The transmissive rate of an infrared image was not affected after the irradiation of 1 MGy. We have developed the fiber-coupled LIBS system to detect plasma emission efficiently in near-infrared region. In addition, we have performed a ray dose rate measurement using an optical fiber of which scintillator is attached to the tip. As a result, the concept of applicability of a probing system using the high-radiation resistant optical fibers has been confirmed.
Ishiyama, Shintaro; Oba, Hironori; Yamamoto, Shunya; Shobu, Takahisa
Kagaku Kogaku Rombunshu, 40(2), p.131 - 136, 2014/03
Times Cited Count：0 Percentile：0(Engineering, Chemical)New micromachining technique of unworkable sapphire was demonstrated by highly coalesced ion implantation and eximer laser irradiation methods. After proton implantation by 0.3 MeV H up to 110
/cm
into sapphire, damaged region was formed beneath 1m depth from the surface of implanted sapphire and blistering was observed by 0.33 MeV H over 110/cm. Ion implanted sapphire behaves peculiar wavelength absorption at 200 nm and ion implanted sapphire by 0.3 MeV H up to 110/cm was irradiated by ArF laser with 3.4 J/cm1 shot and micro trench shape with 1m depth and 5080 m width was observed on the surface of ion implanted sapphire. These results mean that micromachining of sapphire on the order of m width with arbitrarily depth can be possible by highly coalesced ion implantation and laser irradiation techniques.
Miyabe, Masabumi; Oba, Masaki; Iimura, Hideki; Akaoka, Katsuaki; Maruyama, Yoichiro; Oba, Hironori; Tampo, Motonobu; Wakaida, Ikuo
Applied Physics A, 112(1), p.87 - 92, 2013/07
Times Cited Count：19 Percentile：67.04(Materials Science, Multidisciplinary)A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm. The temporal evolution of the ablation plume was investigated in vacuum and helium environments. In vacuum, the flow velocity perpendicular to the sample surface was determined to be 2.7 km/s for neutral atoms and 4.0 km/s for singly charged atoms. From the evolution of the plume in helium we found that an observation time of 3-5 s and an observation height of about 2.5 mm are most suited for obtaining higher sensitivity. Observation times less than 3 s were unsuitable for precise isotope analysis since the spectral modifications arising from the Doppler splitting effect are different between the two uranium isotopes. Using the established conditions, we evaluated the calibration curve linearity, limit of detection, and precision for three samples having different abundances of 
U.
Miyabe, Masabumi; Oba, Masaki; Iimura, Hideki; Akaoka, Katsuaki; Maruyama, Yoichiro; Oba, Hironori; Tampo, Motonobu; Wakaida, Ikuo
Hyperfine Interactions, 216(1-3), p.71 - 77, 2013/04
Times Cited Count：9 Percentile：94.2To determine experimental conditions suitable for isotope analysis, we studied the plume dynamics of uranium. A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm. The temporal evolution of the ablation plume was investigated in 800 Pa helium environment. It was found that the observation at 3-510
s after the ablation at the height of about 2.5 mm are most suited for obtaining higher sensitivity. Using the established conditions, we obtained the limit of detection of the isotope ratio (U/
U) to be 0.01%. In addition, the limit of detection of elemental abundance of uranium in uranium glass was also evaluated.
Miyabe, Masabumi; Oba, Masaki; Iimura, Hideki; Akaoka, Katsuaki; Maruyama, Yoichiro; Oba, Hironori; Tampo, Motonobu; Wakaida, Ikuo
Journal of Applied Physics, 112(12), p.123303_1 - 123303_10, 2012/12
Times Cited Count：9 Percentile：41.36(Physics, Applied)The temporal evolution of the ablation plume of cerium was investigated by absorption spectroscopy. Cerium oxide pellets were ablated in helium by 2nd harmonic radiation from a YAG laser. The lateral velocity of the plume was determined from the magnitude of the Doppler splitting of the absorption spectra. The velocities of neutral and ionized atoms were systematically investigated by varying several parameters. Temporal profiles of the transmittance signal were measured by detuning the probe laser frequency from the atomic resonant frequency in order to evaluate the temporal variation of the lateral velocity. On the basis of the drag force model, the slowing coefficients for atomic and ionic species in helium were evaluated along with the lateral velocity in a vacuum. This study may help in understanding the plume dynamics effect on deposited film properties as well as optimizing experimental conditions for ablation-based spectroscopic analysis.
