Delocalized Nature of the E'-delta Center in Amorphous Silicon Dioxide
  We report an experimetal study by Electron Paramagnetic Resonance (EPR) of E'-delta point defect induced by gamma ray irradiation in amorphous SiO2. We obtained an estimetion of the intensity of the 10 mT doublet characterizing the EPR spectrum of such a defect arising from hyperfine interaction of the unpaired electron with a 29Si (I=1/2) nucleus. Moreover, determining the intensity ratio between this hyperfine doublet and the main resonance line of E'-delta center, we pointed out that unpaired electron wave function of this center is actually delocalized over four nearly equivalent silicon atoms. 
Gianpiero Buscarino, Simonpietro Agnello and Franco Mario Gelardi