Factors controlling the spatiotemporal variation of Cs in seabed sediment off the Fukushima coast; Implications from numerical simulations

Misumi, Kazuhiro*; Tsumune, Daisuke*; Tsubono, Takaki*; Tateda, Yutaka*; Aoyama, Michio*; Kobayashi, Takuya; Hirose, Katsumi*

Journal of Environmental Radioactivity, 136, p.218 - 228, 2014/10

https://doi.org/10.1016/j.jenvrad.2014.06.004

Major controls on spatiotemporal variations of Cs activity in seabed sediments derived from the Fukushima Dai-ichi Nuclear Power Plant accident during the first year after the accident were investigated by using numerical simulations. The model successfully reproduced major features of the observed spatiotemporal variations of Cs activity in sediments. The spatial pattern of Cs in sediments, which mainly reflected the history of Cs activity in the bottom water overlying the sediment and the sediment particle size distribution, became established during the first several months after the accident. Taking Cs activities in sediments in the coastal area and in the vicinity of the power plant into account, increased the simulated total inventory of Cs in sediments off the Fukushima coast to a value on the order of 10 Bq.

Radon inhalation protects mice from carbon-tetrachloride-induced hepatic and renal damage

Kataoka, Takahiro*; Nishiyama, Yuichi*; Toyota, Teruaki*; Yoshimoto, Masaaki*; Sakoda, Akihiro; Ishimori, Yuu; Aoyama, Yutaka*; Taguchi, Takehito*; Yamaoka, Kiyonori*

Inflammation, 34(6), p.559 - 567, 2011/12

https://doi.org/10.1007/s10753-010-9263-7

We assessed whether radon inhalation provided protection from carbon tetrachloride induced hepatic and renal damage in mice. Mice were subjected to intraperitoneal injection of CCl after inhaling approximately 18 kBq/m radon for 6 h. Radon inhalation significantly increased total glutathione content and glutathione peroxidase activity in the liver and kidney. Injection of CCl was associated with significantly higher levels of glutamic oxaloacetic transaminase and alkaline phosphatase activity and creatinine level in serum, and pretreatment with radon significantly decreased the GOT and ALP activity and creatinine level associated with CCl injection, suggesting that radon inhalation alleviates CCl-induced hepatic and renal damage. The t-GSH contents an GPx activity in the liver and kidney of animals pretreated with radon were significantly higher than those of the CCl-only group. These findings suggested that radon inhalation activated antioxidative functions and inhibited CCl-induced hepatic and renal damage in mice.

Optical-parametric chirped-pulse amplification using a positive dispersive material for pulse stretching and compression

Yamakawa, Koichi; Akahane, Yutaka; Ogawa, Kanade; Aoyama, Makoto

Denki Gakkai Hikari, Ryoshi Debaisu Kenkyukai Shiryo OQD-09-61, p.13 - 16, 2009/09

We have proposed and demonstrated a novel optical-parametric chirped-pulse amplification scheme in which an even order dispersion of an idler pulse is compensated by passing through an identical positive dispersive material used for temporal stretching a signal pulse. By compressing the idler pulses having a negatively chirp in this manner, high power sub-100 fs pulses were successfully obtained with only a transparent glass block used for the stretcher and compressor. A feasible design of real world femtosecond laser systems employing this scheme is also discussed.

Controlling the phase matching conditions of optical parametric chirped-pulse amplification using partially deuterated KDP

Ogawa, Kanade; Sueda, Keiichi*; Akahane, Yutaka; Aoyama, Makoto; Tsuji, Koichi; Fujioka, Kana*; Kanabe, Tadashi*; Yamakawa, Koichi; Miyanaga, Noriaki*

Optics Express (Internet), 17(10), p.7744 - 7749, 2009/05

https://doi.org/10.1364/OE.17.007744

Using a partially deuterated KDP crystal for an optical parametric amplifier, we demonstrated ultrabroadband optical parametric chirped-pulse amplification of more than 250 nm bandwidth at a center wavelength of 1050 nm. We numerically show how to control the broadband phase matching conditions at different wavelengths to match center wavelengths of suitable broadband seed sources by adjusting the deuteration level in partially deuterated KDP.

Spectroscopic characterization of ultrashort laser driven targets incorporating both Boltzmann and particle-in-cell models

Sherrill, M. E.*; Abdallah, J.*; Csanak, G.*; Dodd, E. S.*; Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki*; Yamakawa, Koichi; et al.

High-Power Laser Ablation VII (Proceedings of SPIE Vol.7005), p.70051R_1 - 70051R_11, 2008/06

High-energy diode-pumped picosecond regenerative amplification at 999 nm in wavelength with a cryogenically cooled Yb:LuLiF crystal

Akahane, Yutaka; Aoyama, Makoto; Sugiyama, Akira; Kubo, Ryoichi; Ogawa, Kanade; Tsuji, Koichi; Yamakawa, Koichi

Optics Letters, 33(5), p.494 - 496, 2008/03

https://doi.org/10.1364/OL.33.000494

A diode-pumped, cryogenically-cooled Yb:LuLiF regenerative amplifier has been developed for the first time to our knowledge. A chirped-seed pulse was amplified and compressed in the regenerative amplifier, simultaneously, which generated 6-mJ, 13-ps pulses at 999 nm wavelength without a pulse compressor. Simultaneous lasing at 999 nm and 1024 nm, respectively, was demonstrated, which could be used for different frequency generation in the THz region.

Multi-millijoule, diode-pumped, cryogenically-cooled Yb:KY(WO) chirped-pulse regenerative amplifier

Ogawa, Kanade; Akahane, Yutaka; Aoyama, Makoto; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi

Optics Express (Internet), 15(14), p.8598 - 8602, 2007/07

https://doi.org/10.1364/OE.15.008598

Ytterbium (Yb) doped gain media are one of promising laser materials for the next generation of diode-pumped high-power lasers. Yb-doped media have several advantages. It has wide absorption bandwidth, the low quantum defect, and the simple electronic structure. Yb:KY(WO) (Yb:KYW) and Yb:KG(WO) (Yb:KGW) have a large absorption and wide emission cross section, broad emission spectral range, and high thermal conductivity, yielding a high repetition-rate, high-energy, sub-picosecond pulses. However, multi-millijoule-class Yb:KYW or Yb:KGW lasers have not yet been reported so far, excepting a massive, joule-class Ti:sapphire laser pumped Yb:KGW regenerative amplifier. So, We developed a compact diode-pumped, cryogenically-cooled chirped-pulse Yb:KYW regenerative amplifier. An amplified pulse with an energy of 5.5 mJ and a high optical conversion efficiency of 14% is achieved. Regenerative pulse shaping is also used to counter gain narrowing during amplification.

Degenerate optical parametric chirped-pulse amplifier pumped by an Yb:YLF chirped-pulse amplification laser

Aoyama, Makoto; Akahane, Yutaka; Ogawa, Kanade; Tsuji, Koichi; Sugiyama, Akira; Harimoto, Tetsuo*; Kawanaka, Junji*; Nishioka, Hajime*; Fujita, Masayuki*; Yamakawa, Koichi

Reza Kenkyu, 35(6), p.398 - 399, 2007/06

https://ci.nii.ac.jp/naid/10019561213

We have demonstrated optical parametric chirped-pulse amplification by using a diode-pumped Yb:YLF CPA laser system as a pump source and achieved an ultra-broadband amplification of over 200-nm supporting a 12.6-fs duration (3.7 optical cycles) in spite of being operated around degeneracy. By using a two-stage OPCPA with a higher-energy pump pulse, it should be able to produce a terawatt-class, few-cycle laser pulse without complexly and enlarging the system size. Such a laser is useful for the generation of attosecond pulse generation in the xuv region as well as other high field applications.

Spectroscopic characterization of an ultrashort-pulse-laser-driven Ar cluster target incorporating both Boltzmann and particle-in-cell models

Sherrill, M. E.*; Abdallah, J. Jr.*; Csanak, G.*; Dodd, E. S.*; Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki*; Yamakawa, Koichi; et al.

Physical Review E, 73(6), p.066404_1 - 066404_6, 2006/06

https://doi.org/10.1103/PhysRevE.73.066404

A model that solves simultaneously both the electron and atomic kinetics was used to generate synthetic He X-ray spectra to characterize a high intensity ultrashort laser driven Ar cluster target experiment. In particular, level populations were obtained from a detailed collisional-radiative model where collisional rates were computed from a time varying electron distribution function obtained from the solution of the zero dimensional Boltzmann equation. In addition, aparticle-in-cell simulation was used to model the laser interaction with the cluster target and provided the initial electron energy distribution function (EEDF) for the Boltzmann solver. This study suggests that the high density plasma contribution to the time-integrated He spectrum was in a highly non-equilibrium state in both the EEDF and the ion level populations and provides a prediction of 5.7 ps for the average cluster integrity time for this high density state.

Characterization of wave-front corrected 100 TW, 10 Hz laser pulses with peak intensities greater than 10 W/cm

Akahane, Yutaka; Ma, J.-L.; Fukuda, Yuji; Aoyama, Makoto; Kiriyama, Hiromitsu; Sheldakova, J. V.*; Kudryashov, A. V.*; Yamakawa, Koichi

Review of Scientific Instruments, 77(2), p.023102_1 - 023102_7, 2006/02

https://doi.org/10.1063/1.2166669

An improvement of laser-focused peak intensity has been achieved in a JAERI 100-TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system operating at a 10 Hz repetition rate. The Strehl ratio was enhanced to 0.8 by means of a Bimorph deformable mirror with a Shack-Hartmann wavefront sensor. Measurements of optical parameters of the laser pulse and an experimental tunneling ionization yield of helium have practically confirmed focusing to ultra-relativistic intensities of over 10 W/cm within 16 % accuracy.