Structural analysis of radiation damage in zircon and thorite: An X-ray absorption spectroscopic study

Journal Article · · American Mineralogist; (United States)

OSTI ID:5544217

Farges, F; Calas, G ^[1]

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1. Univ. Paris 6 (France)

Metamictization effects have been investigated in zircon, thorite, uranothorite, and thorogummite using X-ray absorption spectroscopy at Zr-K, Th-L{sub III} edges. Extended X-ray absorption fine structure (EXAFS) spectra of metamict samples are characterized by a major contribution due to the O nearest neighbors with some contributions from next-nearest neighbors (Si and Zr in zircon, Si in thorite). In zircon, Zr-O distances decrease by {approx}0.1 {angstrom} while the coordination number of Zr decreases from 8 to 7. In contrast, the eightfold coordination of Th in crystalline thorite is preserved in metamict thorite, Si second neighbors around Zr or Th are generally observed in metamict samples with distances close to those measured in crystalline phases. No other contribution to EXAFS is observed in thorite, but Zr-Zr distances are observed in zircon. They decrease by ca. 0.3 {Angstrom} as a function of zircon metamictization. Metamictization processes are characterized by a loss of medium range order. There is no evidence for decomposition into crystalline oxides. The structural interpretation of EXAFS data must take into account the creation of O vacancies arising from a displacement or tilting of the SiO{sub 4} tetrahedra during metamictization of zircon-like structures. If the cation can take a lower coordination number (as in the case of Zr), a coordination change allows the local structure to be partly maintained during metamictization. If not, as for Th, the local structure is rapidly destroyed.

• OSTI ID: 5544217
• Journal Information: American Mineralogist; (United States), Journal Name: American Mineralogist; (United States) Vol. 76:1-2; ISSN AMMIA; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360605* -- Materials-- Radiation Effects
58 GEOSCIENCES
580000 -- Geosciences
ABSORPTION SPECTROSCOPY
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DATA ANALYSIS
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
MATERIALS
METAMICT STATE
MINERALS
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
RADIATIONS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
SILICATE MINERALS
SPECTROSCOPY
THORITE
THORIUM MINERALS
WEATHERING
X RADIATION
X-RAY SPECTROSCOPY
ZIRCON