Influence of linear energy transfer on the scintillation decay behavior in a lithium glass scintillator

Koshimizu, Masanori*; Iwamatsu, Kazuhiro*; Taguchi, Mitsumasa; Kurashima, Satoshi; Kimura, Atsushi; Yanagida, Takayuki*; Fujimoto, Yutaka*; Watanabe, Kenichi*; Asai, Keisuke*

Journal of Luminescence, 169(Part B), p.678 - 681, 2016/01

We analyzed the effects of linear energy transfer (LET) on the scintillation properties of a Li glass scintillator, GS20. The scintillation time profiles were measured by using pulsed ion beams having different LETs. The rise in the scintillation time profiles was faster for higher LET, whereas the decay part was not significantly different for largely different LETs. The LET effects in the rise was ascribed to the effects of excited states interaction during the energy transfer process from the host glass to the luminescent centers, Ce ions. Supposing that the light yield decreases with LET, the fast rise at high LET was explained in terms of the competition between the energy transfer and the quenching due to the excited states interaction.

System for measuring temporal profiles of scintillation at high and different linear energy transfers by using pulsed ion beams

Koshimizu, Masanori*; Kurashima, Satoshi; Taguchi, Mitsumasa; Iwamatsu, Kazuhiro; Kimura, Atsushi; Asai, Keisuke*

Review of Scientific Instruments, 86(1), p.013101_1 - 013101_5, 2015/01

https://doi.org/10.1063/1.4904872

We have developed a system for measuring the temporal profiles of scintillation at high linear energy transfer (LET) by using pulsed ion beams from a cyclotron. The half width at half maximum time resolution was estimated to be 1.5-2.2 ns, which we attributed mainly to the duration of the pulsed ion beam and timing jitter between the trigger signal and the arrival of the ion pulse. The temporal profiles of scintillation of BaF at different LETs were successfully observed. These results indicate that the proposed system is a powerful tool for analyzing the LET effects in temporal profiles of scintillation.

Application of accelerators for the research and development of scintillators

Shibuya, Kengo*; Koshimizu, Masanori*; Asai, Keisuke*; Muroya, Yusa*; Katsumura, Yosuke; Inadama, Naoko*; Yoshida, Eiji*; Nishikido, Fumihiko*; Yamaya, Taiga*; Murayama, Hideo*

Review of Scientific Instruments, 78(8), p.083303_1 - 083303_7, 2007/08

https://doi.org/10.1063/1.2777152

Nanoparticle formation by pulsed laser ablation of TiO

Yamaki, Tetsuya; Ito, Hisayoshi; Matsubara, Masakazu*; Abe, Hiroaki*; Asai, Keisuke*

Transactions of the Materials Research Society of Japan, 28(3), p.879 - 882, 2003/10

Titanium oxide nanoparticles were formed by pulsed laser ablation of a TiO rutile pellet with a KrF excimer laser ( = 248 nm). The ablation was performed in atmospheres of Ar and O at total pressures ranging from 0.2 and 10 Torr. At a higher pressure than 1 Torr, Ti in the nanoparticles had an oxidation state of 4+ to form TiO. According to the X-ray diffraction analyses, the nanopartiles were found to contain both the anatase and rutile phases, which crystallized through extremely energetic, non-equilibrium reactions in an ablation plume. In contrast, at pressures of 0.2 and 0.5 Torr, the nanoparticles were composed of dominant TiO with a small amount of a less oxidized phase such as TiO. The important result is that the XRD patterns of the samples prepared at 1 and 5 Torr showed the different anatase-to-rutile ratio of the peak intensities. This indicates that the weight fraction of the rutile/anatase crystalline phases can be controlled by the ambient gas pressure.

Synthesis of sulfur-doped TiO by ion implantation

Umebayashi, Tsutomu; Yamaki, Tetsuya; Yamamoto, Shunya; Tanaka, Shigeru; Asai, Keisuke*

Transactions of the Materials Research Society of Japan, 28(2), p.461 - 464, 2003/06

TiO is promising as a photocatalytic material. However, it is active only under UV light irradiation because of its wide band gap (3.0 eV). We recently reported that sulfur (S) doping caused the optical absorption edge of TiO to be shifted into the lower energy region. Based on the theoretical analyses using first principles band calculations, mixing of the S 3p states with the valence band was found to contribute to the bandgap narrowing. In this study presented here, S-doped TiO was prepared by ion implantation and subsequent thermal annealing. S was implanted into the single crystals of rutile TiO with a fluence of 8 10 ions/cm. According to the results of RBS/channeling analysis, irradiation damage recovered after the annealing at 600 C in air. In the annealed crystal, S atoms occupied O sites to form Ti-S bonds, as assessed by XPS.

Sulfur-doping of rutile-titanium dioxide by ion implantation; Photocurrent spectroscopy and first-principles band calculation studies

Umebayashi, Tsutomu; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi; Tanaka, Shigeru; Sumita, Taishi*; Asai, Keisuke*

Journal of Applied Physics, 93(9), p.5156 - 5160, 2003/05

https://doi.org/10.1063/1.1565693

Sulfur (S)-doped titanium dioxide (TiO) was synthesized by ion implantation and subsequent thermal annealing. Compared to the pure TiO, a photocurrent was observed in the lower energy regions for the S-doped TiO. Based on the theoretical analyses by the first principles band calculations using the full potential linearized augmented plane wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the bandgap narrowing in the S-doped TiO. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm ( 2.9 eV).

Visible light-induced degradation of methylene blue on S-doped TiO

Umebayashi, Tsutomu; Yamaki, Tetsuya; Tanaka, Shigeru; Asai, Keisuke*

Chemistry Letters, 32(4), p.330 - 331, 2003/04

https://doi.org/10.1246/cl.2003.330

A sulfur (S)-doped titanium dioxide (TiO) photocatalyst was synthesized by oxidative annealing of titanium disulfide (TiS). TiS turned into anatase TiO when annealed in air. The residual S atoms occupied O-atom sites in the TiO to form Ti-S bonds. The S doping caused the absorption edge of TiO to be shifted into the lower energy region. Consequently, methylene blue adsorbed on the S-doped TiO was photocatalytic decomposed by visible light irradiation.

Band gap narrowing of titanium dioxide by sulfur doping

Umebayashi, Tsutomu; Yamaki, Tetsuya; Ito, Hisayoshi; Asai, Keisuke*

Applied Physics Letters, 81(3), p.454 - 456, 2002/07

https://doi.org/10.1063/1.1493647

Titanium dioxide (TiO) doped with sulfur (S) was synthesized by oxidation annealing of titanium disulfide (TiS). According to the X-ray diffraction patterns, TiS turned into anatase TiO when annealed at 600 C. The residual S atoms occupied O-atom sites in TiO to form Ti-S bonds. The S doping caused the absorption edge of TiO to be shifted into the lower energy region. Based on the theoretical analyses using ab-initio band calculations, mixing of the S 3p states with the valence band was found to contribute to the band gap narrowing.

Formation of hybrid monolayers and langmuir-blodgett-type multilayers from ammonium cations and TiO crystalline nanosheets

Yamaki, Tetsuya; Shinohara, Ryuji*; Asai, Keisuke*

Thin Solid Films, 393(1-2), p.154 - 160, 2001/08

https://doi.org/10.1016/S0040-6090(01)01063-X

no abstracts in English

Ion beam induced crosslinking reactions in poly(di-n-hexylsilane)

Seki, Shuhei*; *; *; *; Yoshida, Yoichi*; Kudo, Hisaaki; Sugimoto, Masaki; Morita, Yosuke; Seguchi, Tadao; *; et al.

Journal of Physical Chemistry B, 103(15), p.3043 - 3048, 1999/00

https://doi.org/10.1021/jp9847080

no abstracts in English