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PACS 42.70.Ce -Glasses, quartz PACS 61.72.jd -Defects and impurities in crystals; microstructure Vacancies PACS 61.72.J--Points defects and defect clusters Abstract -Several E -type defects have been revealed in neutron-irradiated natural and synthetic α-quartz by using electron paramagnetic resonance (EPR) spectroscopy. For the known E 2 center the primary spin Hamiltonian parameter matrices g and A( 29 Si) (hyperfine interaction with 29 Si) have been refined and provide compelling evidence for spin trapping on the long-bond Si atom. The EPR spectra of the new E 11 center demonstrate that the super-hyperfine structure arises from the interaction with 27 Al, the first-ever example of Al-associated E centers in crystalline quartz. The matrices g and A( 29 Si) of E 11 and another new center (E 12 ) support the forwardoriented configuration proposed for the E α center in amorphous silica.

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