  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.
