Point defects in silicates

Thesis/Dissertation · Sun Dec 31 04:00:00 EST 1989

OSTI ID:138413

Priest, V

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
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
36 MATERIALS SCIENCE
58 GEOSCIENCES
AGE ESTIMATION
ALPHA DECAY
ALPHA PARTICLES
DAUGHTER PRODUCTS
ELECTRON SPIN RESONANCE
HIGH-LEVEL RADIOACTIVE WASTES
NEUTRONS
PHYSICAL RADIATION EFFECTS
POINT DEFECTS
QUARTZ
RADIOACTIVE WASTE DISPOSAL
SILICATE MINERALS
SITE CHARACTERIZATION
THORIUM
URANIUM
YUCCA MOUNTAIN
Yucca Mountain Project