2002 Fiscal Year Final Research Report Summary
Study on the crystal structure of deep sections of Antarctic ice cores
| Project/Area Number |
12440077
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | Hokkaido University |
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Principal Investigator |
HORI Akira Hokkaido Univ., Inst. of Low Temp. Sci., Assist. Prof., 低温科学研究所, 助手 (60280856)
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| Co-Investigator(Kenkyū-buntansha) |
NARITA Hideki Hokkaido Univ., Inst. of Low Temp., Assoc. prof., 低温科学研究所, 助教授 (20001662)
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| Project Period (FY) |
2000 – 2002
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| Keywords | ice core / crystal structure / proton configuration / X-ray diffraction / ice / order-disorder transition / structure / dislocation density |
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| Research Abstract |
Characteristic features in Antarctic ice cores have been observed by Raman and incoherent inelastic neutron spectra, which have been attributed to proton ordering in ice structure. In this study, to elucidate the characteristic crystal structure of ice cores from Antarctica were investigated mainly by X-ray diffraction. The followings are the results in this research:
(1) X-ray diffraction study of structure of ice crystal
X-ray rocking curve measurements were conducted for deep sections of Vostok ice core and the dislocation density was determined from the width of the profiles. The dislocation density decreases from 10^<12>m^<-2> to 10^8 m^<-2>, as depth increases between 3200 and 3611 m. The dislocation density was lower in deepest sections because^the ice was formed by the refreezing of Vostok Lake water in a long period.
(2) X-ray powder diffraction study of crystal structure
The observed profiles by X-ray powder diffraction did show sample or depth dependency. The (1121) reflection w
… More
hich is characteristic of ordered ice (ice XI) was scarcely observed in any samples. This is because the intensity of this reflection is expected to be very low and, therefore, strong X-ray source like synchrotron radiation is necessary in a further study. X-ray diffuse scattering measurements are also important in the further study.
(3) Lattice constants determined by X-ray powder diffraction
Lattice constants of ice core samples were determined by Reidtveld analysis of X-ray powder diffraction profiles. The lattice constants of ice core samples are larger than that of laboratory ice and increase with the depth although they are expected to be smaller due to residual stress. The origin of this behavior should be investigated in a further study.
(4) Raman Spectra of deformed ice
To reveal the origin of the reported characteristic spectra of Antarctic ice, Raman spectra for deformed ice were measured. However, no significant change was observed. Thus, the deformation of ice in the Antarctic ice sheet is not a possible reason for the characteristic spectra.
(5) Formation process of clathrate hydrate and ice crystal structure
Molecular dynamics simulations elucidated a new diffusion mechanism of gases in ice during clathrate hydrate formation from ice. We first found that in the diffusion process gas forms a characteristic intermediate structure breaking a hydrogen bond between a pair of water molecules. Less
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