Point defects in silicates
Topaz is a wide band gap insulating crystal with four Al{sub 2}F{sub 2}SiO{sub 4} formula units per orthorhombic unit cell and containing isolated SiO{sub 4} tetrahedron. Electron spin resonance (ESR), UV-VIS spectrophotometry, photoluminescence, and isochronal annealing were used to study the point defects introduced by fast-neutron bombardment or by alpha decay recoils. The superoxide radical is characterized by a single hole-like spin 1/2 signal with principle g-values g{sub xx} = 2.0055, g{sub zz} = 2.0407 and the major axis of the defect points along 0.356{cflx a} + 0.152{cflx b} + 0.922{cflx c}. The superoxide anneals near 650C. Two polarization dependent absorptions occur in the UV due to the transitions {sup 2}II{sub g} {yields} {sup 2}II{sub u} and {sup 2}II{sub g} {yields} {sup 2}{Delta}{sub u}. The former has an oscillator strength of 0.06. The 2.5 eV polarization dependent luminescence is due to the transition {sup 2}II{sub g} {yields} {sup 2}II{sub u}. The {sup 2}{Delta}{sub u} {yields} {sup 2}II{sub u} is non-radiative. The doubly occupied dangling silicon bond, the blue center, is characterized by a 2 eV polarization dependent absorption and is non-paramagnetic. The transition dipole for this absorption points in the direction 0.93{cflx a} + 0.210{cflx b} + 0.305{cflx c} and the oscillator strength is approximately 2.0 {times} 10{sup {minus}3}. The blue center anneals at 500C. This dangling bond defect is one of two models proposed for a similar 2 eV absorption in silica glass. The defects in quartz (SiO{sub 2}) were introduced by the recoil nuclei after alpha decays of uranium, thorium, and their daughters in natural abundances. The accumulating damage provides a geological clock by which the age of the quartz can be found. The sample came from Yucca Flats, Nevada, the proposed site of a nuclear waste dump.
- Research Organization:
- Missouri Univ., Columbia, MO (United States)
- OSTI ID:
- 138413
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1989
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
36 MATERIALS SCIENCE
SILICATE MINERALS
PHYSICAL RADIATION EFFECTS
POINT DEFECTS
YUCCA MOUNTAIN
SITE CHARACTERIZATION
AGE ESTIMATION
ALPHA DECAY
ALPHA PARTICLES
DAUGHTER PRODUCTS
ELECTRON SPIN RESONANCE
HIGH-LEVEL RADIOACTIVE WASTES
NEUTRONS
QUARTZ
RADIOACTIVE WASTE DISPOSAL
THORIUM
URANIUM
Yucca Mountain Project