[en] Static magnetic susceptibilities have been measured on an α-quartz single crystal that had been irradiated with fast neutrons. Above 65 K, the radiation-induced paramagnetism obeys the Curie law, indicating the presence of non-interacting centres. The low-temperature measurements result in a field dependent susceptibility comparable to the effect of the Brillouin saturation of non-interfacing centres. When the calculated susceptibility values are subtracted from the measured data, then the differences behave-over the whole temperature range-as the susceptibility of antiferromagnetically coupled electrons. On the same sample also, low-temperature 20.9 GHz electron spin resonance measurements have been carried out. The major resonance line is attributed to the E' centre. The general behaviour clearly corroborates the presence of interactions; the effect does not show anisotropy. (author)