Gamma-irradiated fused quartz has been investigated at 290 K using 1.7 and 9.8 GHz electron spin echo spectroscopy. Three pulse stimulated echo sequences were used in this study because the electron spin echo signal decay was too fast using two-pulse echo sequences. It was found that no electron spin echo envelope modulation could be observed at 9.8 GHz but that a small relative amplitude envelope modulation signal could be observed at 1.7 GHz if the time interval between the first and second pulses was 1.0 or 3.0 μs but not for 2.0 μs. It was concluded that this modulation is due to the magnetic dipole interaction between the E′1 centers and 29Si nuclei. The natural abundance of this isotope of silicon is 4.7%, I=1/2, and μ=−0.5553 μN. Unsuccessful attempts were made to model this modulation signal assuming that the E′1 center was located at oxygen and silicon vacancies in the hexagonal lattice of quartz. It was concluded that the E′1 center behaves as if it does not interact with the nearest- or next-nearest-neighbor 29Si nuclei. Acceptable agreement was obtained if this electron center is located at a silicon vacancy and only interacts with all nuclei located outside a 0.5 nm radius sphere. This implies that the point charge model may not be applicable because the electron appears to be delocalized within this spherical volume.