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Np and 
Am gamma ray regionsFukuda, Tatsuo; Kobata, Masaaki; Shobu, Takahisa; Yoshii, Kenji; Kamiya, Junichiro; Iwamoto, Yosuke; Makino, Takahiro*; Yamazaki, Yuichi*; Oshima, Takeshi*; Shirai, Yasuhiro*; et al.
Journal of Applied Physics, 132(24), p.245102_1 - 245102_8, 2022/12
Times Cited Count：1 Percentile：5.58(Physics, Applied)Direct energy conversion has been investigated using Ni/SiC Schottky junctions with the irradiation of monochromatized synchrotron X-rays simulating the gamma rays of Np (30 keV) and Am (60 keV). From current-voltage measurements, electrical energies were obtained for both kinds of gamma rays. The energy conversion efficiencies were found to reach up to 
1.6%, which is comparable to those of a few other semiconducting systems reported thus far. This result shows a possibility of energy recovery from nuclear wastes using the present system, judging from the radiation tolerant nature of SiC. Also, we found different conversion efficiencies between the two samples. This could be understandable from hard X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements, suggesting the formation of Ni-Si compounds at the interface in the sample with a poor performance. Hence, such combined measurements are useful to provide information that cannot be obtained by electrical measurements alone.
Akagi, Hiroshi*; Kumada, Takayuki; Otobe, Tomohito*; Itakura, Ryuji*; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Chemistry Letters, 49(4), p.416 - 418, 2020/04
Times Cited Count：1 Percentile：3.24(Chemistry, Multidisciplinary)Akagi, Hiroshi*; Kumada, Takayuki; Otobe, Tomohito*; Itakura, Ryuji*; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Applied Physics B, 124(1), p.14_1 - 14_8, 2018/01
Times Cited Count：2 Percentile：12.36(Optics)We propose and numerically simulate a method of laser isotope separation based on field-free alignment of isotopologues, utilizing an intense switched nanosecond (ns) laser field which is slowly turned on and rapidly turned off at the peak with the falling time of 200 fs. The femtosecond (fs) laser induced alignment of molecules including a heavy atom is severely disturbed by ionization because of their small ionization potential. Our simulations for I
Br and I
Br isotopologues demonstrate that the switched ns laser field can make isotopologues well-aligned with the reduced ionization probability at the laser intensity which is an order-of-magnitude lower than a typical intensity for field-free alignment induced by a fs laser field.
Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Physical Review A, 91(6), p.063416_1 - 063416_7, 2015/06
Times Cited Count：8 Percentile：39.56(Optics)We propose a strategy of isotope-selective ionization for a binary mixture of isotopologues of homonuclear diatomic molecules, utilizing field-free alignment with a train of femtosecond laser pulses. Field-free alignment can be achieved simultaneously for two isotopologues consisting of two atoms with the same atomic mass number 
or 
, utilizing a pulse train with their time interval of T
= T() = T(), where T() and T() are the rotational revival times of the isotopologues. We demonstrate experimentally that a train of four alignment pulses with their interval of T ( = 14, = 15) creates transiently aligned 
N
and anti-aligned 
N just before T/2 after the last pulse, and vice versa just after T/2. Highly isotope-selective N ionization is achieved at these timings with another femtosecond laser pulse, which induces the non-resonant multiphoton ionization with the cross section remarkably depending on the angle between the molecular axis and the laser electric field direction. The ion yield ratio I(N
)/I(N) ranges from 0.49 to 2.00, which is wider than the range obtained with single alignment pulse.
Kondo, Masato; Oshima, Yasuhiro*; Tsubouchi, Masaaki
Chemical Physics Letters, 591, p.317 - 322, 2014/01
We have investigated dielectric relaxation in aqueous ionic solutions by terahertz time-domain spectroscopy to elucidate the ionic hydration effect on the water structure. In the low frequency region (
1.0 THz), the dielectric spectra decreased in amplitude with decreasing size of dissolved cations, which indicates the deceleration effect of water within the hydration shell. On the other hand, in the high frequency region (1.0-1.8 THz), the spectra increased in amplitude as compared to that of pure water. This finding indicates dissolved ions weaken the hydrogen bonding of water in ionic solution and induce the structure breaking effect beyond the hydration shell.
Akagi, Hiroshi; Kasajima, Tatsuya; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Applied Physics B, 109(1), p.75 - 80, 2012/10
Times Cited Count：16 Percentile：59.06(Optics)We demonstrate a laser nitrogen isotope separation, which is based on field-free alignment and angular dependent ionization of N and N isotopomers. A linearly-polarized short laser pulse (
795 nm, 
60 fs) creates rotational wave packets in the isotopomers, which periodically revive with different revival times as a result of different moments of inertia. Another linearly-polarized short laser pulse (795 nm, 60 fs) ionizes one of the isotopomers selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio 
[= 
(N)/(N)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
Optics Letters, 37(17), p.3528 - 3530, 2012/09
Times Cited Count：20 Percentile：65.83(Optics)A novel technique for the terahertz (THz) tomography of a photo-induced carrier that is based on optical-pump THz-probe time-resolved reflection spectroscopy using counter-propagation geometry of the pump and probe pulses has been proposed. Transient reflection due to the photo-induced carrier provides information about the physical properties and spatial distribution separately. We have experimentally demonstrated this method using a silicon wafer. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations, assuming an exponential distribution of the photo-induced carrier density.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
Journal of Physical Chemistry A, 114(42), p.11202 - 11209, 2010/07
Times Cited Count：13 Percentile：38.97(Chemistry, Physical)When neutral NO molecules are partly ionized in intense laser fields (
35 TW/cm
), a hole in the rotational wave packet of the remaining neutral NO is created by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed and then the characteristic feature that the population at higher 
levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schrodinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.
Yoneda, Yasuhiro; Abe, Hiroshi; Oshima, Takeshi; Uchida, Hirohisa*
Journal of Applied Physics, 107(9), p.093505_1 - 093505_6, 2010/05
Times Cited Count：8 Percentile：32.92(Physics, Applied)An Mg-Fe alloy system prepared through mechanical alloying was structurally analyzed. Mechanical alloying can produce single-phase bcc alloys using Mg concentrations up to about 15 mol%. Use of conventional average structure analysis and X-ray pair-distribution function method enabled the long-range and short-range order structures of the Mg-Fe alloys to be bridged. The substituted Mg atoms were randomly arranged in the low-Mg composition but started to have an order structure. The partially ordered Mg-Fe alloy undergoes an austenitic (cubic) to martensitic (orthorhombic) phase change, as increasing Mg composition.
Yoneda, Yasuhiro; Tamura, Kazuhisa; Abe, Hiroshi; Oshima, Takeshi; Morimoto, Ryo*; Uchida, Hirohisa*; Mizuki, Junichiro
Transactions of the Materials Research Society of Japan, 33(4), p.1053 - 1056, 2008/12
The effect of ion irradiation on palladium (Pd) metal was investigated by hydrogen-absorption measurements, SEM microscopy and synchrotron X-ray diffraction. N
irradiation was made with an acceleration energy 350 keV. The initial hydrogen absorption rate of the irradiated Pd was three times larger than that of non-irradiated Pd. The microscopic structure was investigated by using the pair-distribution function (PDF) obtained by X-ray diffraction. Although the average structure of the Pd was f.c.c, the Pd atoms displaced and two occupancy sites are revealed. This site occupancy is closely related with the hydrogen-absorption rate.
Amano, Hikaru; Yamamichi, Miwako*; Baba, Masami*; Momoshima, Noriyuki*; Sugihara, Shinji*; Ueda, Yusuke*; Nakamura, Yasuhiro*
JAEA-Conf 2008-003, p.84 - 87, 2008/04
no abstracts in English
Nakagawa, Sho*; Hori, Fuminobu*; Chimi, Yasuhiro; Ishikawa, Norito; Kitagawa, Michiharu*; Oshima, Ryuichiro*; Tobita, Toru; Taniguchi, Ryoichi*; Suzuki, Masahide; Iwase, Akihiro*
Nuclear Instruments and Methods in Physics Research B, 257(1-2), p.397 - 401, 2007/04
Times Cited Count：4 Percentile：34.84(Instruments & Instrumentation)Supersaturated Fe-1.2wt.%Cu alloys were irradiated with 200-MeV Xe and 200-MeV Au ions at elevated temperatures. To make an irradiated region and an unirradiated region in a specimen, a masking plate was put on the specimen during the irradiation. After the irradiation, the hardness was measured by using a conventional microhardness tester or a nano-indenter. We have found that the hardness only in irradiated region increases by the irradiation. The boundary of irradiated and unirradiated regions can be clearly identified by the difference in hardness. The present result implies that swift heavy ion irradiation can be used for the local modification of hardness in supersaturated alloys.
Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
We have been demonstrating new laser isotope separation methods utilizing molecular rotation control with femto-second laser pulses. In the present work, we demonstrate for nitrogen isotopologues (N and N) that one of the isotopologues can be rotationally excited by four femto-second laser pulses with the pulse interval same as the rotational period (8.38 ps for N, 8.98 ps for N).
Kimura, Atsushi; Koizumi, Mitsuo; Toh, Yosuke; Oshima, Masumi; Mizumoto, Motoharu; Goto, Jun*; Arai, Yasuo*; Sagara, Masahiro*; Iri, Shinichi*; Kobayashi, Hirotsugu*; et al.
no journal, ,
To measure neutron cross-section data of minor actinides, we construct a Ge-spectrometer utilizing multiple 
-ray detection method. This spectrometer consists of 30 Ge crystals (40 detector outputs) and 128 BGO anti-Compton shields. Generally, a data acquisition system for such a big Ge spectrometer consists of many NIM modules; it requires large space and huge cost. To overcome these problems, we developed a new data acquisition system with digital signal processing techniques. We reported the conceptual design (and cost) in NSS 2004. In this NSS 2005, we report basic performance of this system (energy resolution, dead time and so on) and results of experiments with the Ge-spectrometer. We measured the energy resolution with a Eurisys clover detector, which is one component of the Ge-spectrometer. Obtained FWHMs (2.5 - 2.8 keV at 1.33 MeV) show good performances as normal MCA even with short shaping time and much higher channel density. The dead time of this system is only 3.2 micro sec per event.
Onodera, Naoyuki; Aoki, Takayuki*; Idomura, Yasuhiro; Yamashita, Susumu; Kawamura, Takuma; Asahi, Yuichi; Ina, Takuya; Hasegawa, Yuta; Sugihara, Kenta; Shimokawabe, Takashi*; et al.
no journal, ,
no abstracts in English
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
no journal, ,
Molecules in intense laser fields are rotationally excited through the non-adiabatic interaction between the induced dipole moment and the laser field. As the intensity of the laser fields increases, the ionization proceeds significantly. In this study, we observed the rotational state distribution of NO irradiated with intense laser pulses using a spectroscopic approach. We also calculated a time-dependent Schrodinger equation for the rotational excitation taking into account of the ionization.
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
We have proposed a novel technique for the THz tomography of photo-induced carrier based on the optical-pump THz-probe reflection spectroscopy with the counter-propagated pump and probe pulses. We have experimentally demonstrated it with silicon. The obtained complex reflection can be reproduced by the exact solution of the Maxwell equations.
Tsubouchi, Masaaki; Yokoyama, Atsushi; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
no abstracts in English
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
We have proposed a novel technique for the THz tomography of photo-induced carriers based on optical-pump THz-probe reflection spectroscopy with the counter-propagated pump and probe pulses. We have experimentally demonstrated it with silicon. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations.
