Chalcogenide glass GeS11, is irradiated by fast neutrons step by step within the range 1 × 1016 and 1 × 1019 neutrons cm−2. The creation of β and γ crystalline sulphur modifications in irradiated samples is interpreted as a consequence of so called thermal spikes, which are present in the small volume during interaction events. This is demonstrated by scanning electromicrographs. The evolution is shown of the sulphur crystalline modifications as a function of the neutron dose.