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Journal Articles

Swift heavy ion irradiation effects in nanocrystalline gold

Chimi, Yasuhiro; Iwase, Akihiro*; Ishikawa, Norito; Kobiyama, Mamoru*; Inami, Takashi*; Kambara, Tadashi*; Okuda, Shigeo*

Nuclear Instruments and Methods in Physics Research B, 245(1), p.171 - 175, 2006/04

 Times Cited Count:13 Percentile:30.44(Instruments & Instrumentation)

We have studied effects of irradiation with energetic particles on defect accumulation in nanocrystalline gold (nano-Au). The specimens of nano-Au foil (3-5 $$mu$$m thickness) with various grain sizes (23-156 nm) are prepared by the gas deposition method and subsequent thermal annealings. Irradiations of the specimens with 60-MeV $$^{12}$$C ions, 3.54-GeV $$^{136}$$Xe ions or 2.0-MeV electrons are performed at low temperature. The defect accumulation behavior is observed by measuring the electrical resistivity change during irradiation. Through an analysis of defect accumulation behavior, cross-sections for defect production, $$sigma$$$$_{d}$$, and annihilation, $$sigma$$$$_{r}$$, in nano-Au increase monotonically as the grain size decreases. These results are considered to be caused by the existence of a large volume fraction of the regions near grain boundaries in nano-Au where the threshold energy for atomic displacements, E$$_{d}$$, becomes lower than in polycrystalline gold. The possibility of electronic excitation effects in nano-Au is also discussed.

Journal Articles

Effects of high-energy ion irradiation in bismuth thin films at low temperature

Chimi, Yasuhiro; Ishikawa, Norito; Iwase, Akihiro*

Materials Research Society Symposium Proceedings, Vol.792, p.379 - 384, 2004/00

We have studied high-energy ion irradiation effects in bismuth by measuring the electrical resistivity at low temperature in relation to its structural change. Bismuth thin films (300-600 $AA  thick) are irradiated below $sim$$10 K with several kinds of energetic (100-200 MeV) heavy ions. The resistivity of the specimen is measured in-situ at $$sim$$7 K during irradiation. After irradiation, annealing behavior of the resistivity is observed up to $$sim$$35 K. The temperature dependence of the resistivity during annealing shows an abrupt increase around 20 K, implying re-crystallization of irradiation-induced amorphous region. Since amorphous bismuth also shows a superconducting transition below $$sim$$6 K, high-density electronic excitation due to energetic heavy-ion irradiation may induce columnar region of superconducting amorphous bismuth in normal crystalline bismuth. We are trying to detect the superconducting transition as a result of irradiation-induced amorphization.

Journal Articles

Depth-dependent and surface damages in MgAl$$_{2}$$O$$_{4}$$ and MgO irradiated with energetic iodine ions

Aruga, Takeo; Katano, Yoshio*; Omichi, Toshihiko*; Okayasu, Satoru; Kazumata, Yukio*; Jitsukawa, Shiro

Nuclear Instruments and Methods in Physics Research B, 197(1-2), p.94 - 100, 2002/11

 Times Cited Count:5 Percentile:63.68(Instruments & Instrumentation)

no abstracts in English

Journal Articles

The Interpretation of surface damages in Al$$_{2}$$O$$_{3}$$, MgAl$$_{2}$$O$$_{4}$$ and MgO irradiated with energetic iodine ions

Aruga, Takeo; Katano, Yoshio*; Omichi, Toshihiko*; Jitsukawa, Shiro

Surface & Coatings Technology, 158-159, p.444 - 448, 2002/09

no abstracts in English

Oral presentation

Atomic structure of ion tracks in fluorite structure oxides; Comparison with CeO$$_{2}$$ and ZrO$$_{2}$$

Takaki, Seiya

no journal, , 

Oxide ceramics with fluorite-structure have been studied as advanced nuclear application, so it is important to clarify the irradiation-induced microstructure. Especially, radiation damage induced by fission fragments with 70-100 MeV, induce high-density electronic excitation in the materials to result in forming cylindrical defect, so called ion track. This study aims to clarify and compare with the structure of ion tracks in CeO$$_{2}$$ and cubic ZrO$$_{2}$$ (YSZ) irradiated with swift heavy ions. It was shown that the density of vacancy at the core damage region of ion tracks is increased and the O anion lattice is preferentially disordered at such region. On the other hand, the size and the areal density of ion tracks in YSZ is smaller than those of CeO$$_{2}$$. The difference of ion tracks between CeO$$_{2}$$ and YSZ is presumably due to the difference in the recovery process from the thermal spike regime, which is influenced by the presence of structural vacancy in oxide sublattice.

Oral presentation

High density electronic excitation damage in fluorite structure oxides

Takaki, Seiya; Yasuda, Kazuhiro*; Matsumura, Sho*; Ishikawa, Norito

no journal, , 

Advanced nuclear application materials are irradiated by fast neutrons, electrons, a particles and fission fragments, so formation of radiation damage and microstructure evolution are induced by pile-up effect of those radiation. Behavior of point defects in materials which has ion and covalent bonding is influenced by electronic excitation. Especially, high-density electronic excitation damage induced by fission fragments, induce to form cylindrical defect, so called ion track in the materials to result in influence for microstructural evolution in fuel materials. This study aims to clarify the structure of ion tracks in CeO$$_{2}$$ and cubic ZrO$$_{2}$$ (YSZ) irradiated with swift heavy ions by using several transmission electron microscopies. It was shown that the density of vacancy at the core damage region of ion tracks is increased and the O anion lattice is preferentially disordered at such region. In addition to, high density dislocation was formed in CeO$$_{2}$$ with irradiated by high fluence. This result support STEM observation. In case of YSZ, the size and the areal density of ion tracks is smaller than those of CeO$$_{2}$$. The difference of ion tracks between CeO$$_{2}$$ and YSZ is presumably due to the difference in the recovery process from the thermal spike regime, which is influenced by the presence of structural vacancy in oxide sublattice.

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